Mechancis

Introduction

A force can be defined as any kind of push or pull on an object in an attempt to change the object's state of rest or motion.

  • The symbol for force is F.
  • The Sl unit for force is the Newton (N).
  • Any force (F) has a certain magnitude and
  • Force is thus a vector quantity and can be e'g'  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

Note:

  • When a force is exerted, there are always two objects involved.
  • The objects interact with each other.
  • They can be in direct contact with each other, or they can interact with each other without direct contact (refer to Newton tlt).

KINDS OF FORGE: CONTACT FORGES AND NON-CONTACT FORCES

Most forces are contact forces, i.e. forces that objects exert on each other when they touch or are connected to one another.

An applied force (FA)

A force that is externally applied to an object, e.g. push or pull or engine force.

Normal force (N or FN)

Normal force:

  • is the force exerted by a flat surface (plane) on an object with which it is in contact.
  • always acts at right angles (perpendicular (r)) to the surface.
  • is equal to the gravitationalforce Fn, or the net of Fn and all other forces acting r to the surface. push or pull or engine force.
 You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

A normal force is the force which a surface exerts on an object with 'h which it is in contact, and which is perpendicular to the surface.

Frictional force (ƒ or Ffr)

Frictional force:

  • is caused by one surface moving/tending to move over another, while in contact
  • resists the movement of an object (prevents it from moving or makes it move more slowly).
       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
  • is parallel to the surface but is in the opposite direction to object moves/tends to move.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

A frictional force is a contact force that opposes the :' motion of an object and which acts parallel to the surface.

Static frictional force (ƒ s)

  • An object that is not being set in motion by any forces acting on it by pushing or pulling, experiences a static frictional force.
  • The static frictional force is equal in magnitude to the applied force (fs = FA), as the forces are in equilibrium (object is at rest).

lnvestigate the static frictional force on a stationary object

  • An object at rest, on which no applied force is acting, experiences no static frictiona! force.
  • Attach a spring balance calibrated in newtons to the object and apply a specific force by pulling the spring balance to a certain reading. lf the object remains at rest, it will experience a frictional force equal in magnitude to the applied force.
  • Gradually increase the applied force until the object is at the point of breaking contact with the surface and is starting to move. The static frictional force increases together with the applied force and has its maximum value (/"'u') just before the start of motion.

Assume the applied force (FA) = 300 N left and the object is at the point of moving :

Fnet = FA + ƒsmax = 0 (vector sum forces = 0 N)
ƒsmax = -FA = 300 N right

 You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

lf the applied force is larger than ƒsmax, the resultant (net) force (Fnet = FA + ƒk) will accelerate the object.

The static frictional force is the force that opposes the tendency of motfol of a stat1onary object relative to- a surface

Calculate the maximum static frictional force (ƒsmax)

  • The maximum static frictional force on an object depends on two factors, namely:
    • the normal force (N) that the plane exerts on the object. The greater the weight of the object, the greater the normal force of the plane on the object (the harder the surfaces press against each other). A greater applied force is now required to get the object moving. ƒsmax ∞ N
    • the material of the surfaces: the roughness and composition of the materials determines the magnitude of the frictional force between two surfaces.
  • μs is a proportionality constant for the ratio ƒsmax / N . The value of μs is unique for every combination of two surfaces experience friction. If the combination is frictionless then μs = 0. For very rough or sticky surface combinations, μs can become quite large (usually 0 < μs ≤ 1). It has no units. therefore, it follows that :

      ƒsmax = μsN

      where: ƒsmax = maximum static frictional force in newton (N)

      μs = coefficient of static friction

      N = normalforce in newton (N)

  • The frictional force ƒs (while the object is at rest) < ƒsmax, and ƒs (just as the object starts moving) = ƒsmax ƒs ≤ μsN
  • On a horizontal plane:
    • lf there are no other perpendicular forces or components of forces on the plane:
 You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
  • On an inclined plane:  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • The gravitational pull on the object is drrected directly downwards to the centre of the earth. Therefore, this force is not perpendicular to the surface (as with horizontal surfaces), but is between the inclined plane and the plane perpendicular to the inclined plane.
    • Consequently, the weight is two dimensional and can be resolved into two useful components, i.e.:
      • the component parallel to the inclined plane (Fn,,) that tends to make the object slip down the plane. This value increases as the angle of inclination increases.
      • the component perpendicular to the inclined plane (Fn,)that tends to push/hold the object against the plane. This value decreases as the angle of inclination increases.
 You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

Determine the coefficient of static friction (μs) of two specific materials Consider an object that is at rest on an inclined plane.

 You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Fnet = fs + FgII = 0 (vector sum of forces = 0 N)
    ∴ ƒs = Fs + FgII (magnitudes only)

  • lf the angle of the inclined plane is increased gradually, a point is reached where the object is at the point of sliding down.
  • Now the frictional force is at a maximum ƒsmax) The coefficient of static friction (μs) of the materials in contact with each other can be calculated as follows:
       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

Kinetic frictional force (ƒk)

  • As soon as an object is set in motion, it no longer experiences static frictional force, but rather a kinetic frictional force counteracting its motion.
  • A smaller applied force is required to keep an object moving at a constant velocity than to get it to move from a position of rest, therefore:
    ƒk < ƒsmax
  • The kinetic frictional force depends on:
    • the normal force of the plane on the object: ƒs ∝ N
    • the coefficient of kinetic friction (μk) of the surfaces that move over each other (μk is a proportionality constant and its value depends on the type of materials that are in contact with each other). Therefore:
      ƒk = μkN

Non-contact forces are the forces that objects exert on each other over a distance, without the objects touching each other.

Examples of non-contact forces

  • The gravitational force (Fg) of any object on any other object with mass.
    • The earth exerts a gravitational force on any object with mass on or near its surface. It is also called its weight, and is calculated as follows: w = mg [g = 9,8 m.s-2 (gravitational acceleration)]
    • The force is directed towards the centre of the earth, i.e. directly downwards.
  • Magnetic forces, attractive or repulsive, between magnetic objects.
  • Electrostatic forces, attractive or repulsive, between charges (charged objects).

The object/s of interest are drawn and all the forces to and from the object are indicated by arrows. The force arrows point in the direction of the force:

  • A pull force or brake force, e.g. frictional force, usually originates on the object and points away from it.
  • An external push force usually originates elsewhere and ends on the object.

The object is represented by a dot and all the forces that act on the object are indicated by arrows pointing away from the dot.

 You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

When more than one force acts on an object, the resultant/net force is determined by adding up all of the forces and components of forces in the same direction (x or y direction) by means of vector addition.

Forces in one direction on an obiect (at rest or moving)

  • Horizontal
  • (object that is being pushed or pulled over a horizontal surface)

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
  • Vertical
  • (object that moves vertically through the air or is suspended from a cable/rope, e.g. a spacecraft/elevator)

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
  • On an inclined plane
  • (object that is at rest or moving on a slope)

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Forces in two directions on an object

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    NEWTON'S FIRST LAW OF MOTION

    • Before the middle of the 16th century, scholars believed that a force was needed to keep an object moving continuously. (ln practice, you move an object by pushing or pulling it, but it comes to a standstill soon after you stop pushing or pulling.)
    • The scientist Galileo Galilei was the first person to realise that friction resists the motion of an object:
      • He did practical investigations and proved that as the friction between an object and the surface on which it moves is reduced, the longer the object takes to stop.
      • He came to the conclusion that if it were possible to eliminate friction completely, a moving object would continue to move, unrestricted, at a constant velocity in a straight line (without the influence of forces).
    • lsaac Newton (1643 - 1727) expanded on Galilei's work and did further studies on forces and motion.
    • Newton formulated his first law of motion, summarising this theory:
    • When the resultantinet force equals zero (Fnet = 0 N) the forces are in equilibrium, or they counterbalance each other. The object then maintains its state of rest or motion.
    • The property of a body that enables it to resist change in its state of motion is called inertia.
    • The greater the mass of a body, the greater its inertia.

      Example: lt is more difficult for a bus full of passengers to come to a stop than an empty bus.

    ln the following cases there is no resultant force on the person/object and the state of rest or motion is maintained:

    • When the brakes of a moving vehicle are applied to bring it to a stop, no force is exerted on the occupants of the car and they will continue moving forward.
    • When a car or bus starts moving, the occupants tend to move backwards.
    • lf a sheet of paper is swiftly pulled from underneath a glass of water, the glass does not move along with it. (The force is only exerted on the paper.)

    lmportance of safety belts

    Safety belts perform a very important function in protecting the occupants of a vehicle from their own inertia when it suddenly comes to a stop. For example, during a crash:

    • A person in a moving vehicle travels at the same velocity as the vehicle.
    • lf the vehicle suddenly stops, the person continues to travel at the same velocity due to his inertia.
    • Therefore, a safety belt keeps the person in his seat and prevents him from crashing through the windscreen and being thrown from the vehicle

    Example 1:

    Explain how a person's inertia causes him to move 'backwards'when a car or bus starts moving.

    Solution:

    A person sitting in a stationary car/bus will try to maintain his state of rest when the vehicle starts moving. Therefore, when the carlbus moves fonrrards, it moves 'out from under the person' and he appears to move backwards.

    NEWTON'S SEGOND LAW OF MOTION

    • From Newton l, it follows that if the resultant/net force on an object is zero (Fnet = 0 N), its state of rest or motion remains unchanged.
    • lf a net force were exerted on an object (Fnet ≠ 0), the state of rest or motion of the object will change:
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Problems invorving one object upon which one or more forces act

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Consider a system of two bodies that are in contact or connected to each other and move or accelerate together. For example:

    • Both bodies A and B are on a flat horizontal plane, with or without friction.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • One body A on a horizontal plane, with or without friction, and a second body B, hanging vertically from a string over a frictionless pulley.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • Both bodies A and B are on an inclined plane, with or without friction.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • Both bodies A and B are hanging vertically from a string over a frictionless pull  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • ldentify the forces on each of the bodies:
      • lf a pull force FA is exerted on B (or A), the string tightens and a tensile force T is present at both ends of the string.
      • A and B experience an equal tensile force (T) in opposite directions.
      • While the length of the string between them is constant, they have the same acceleration.
      • The gravitationalforce on objects moving vertically forms part of Fn.l and accelerates the system.

    Application: Steps in problem-solving

    • Draw a force or free-body diagram for each of the objects.
    • Determine Fnsl for each object. State a separate equation, Fnet = ma, for both objects. (Remember, a is the same for both,)
    • lf both the acceleration a and one of the forces are unknown, a can be calculated by simultaneous solving of the equations. ,
    • Substitute a back into one of the equations to calculate the contact force : ." between the objects or the tensile force in the string.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    NEWTON'S THIRD LAW OF MOTION

    Newton II (Fnet = ma) applies to a single object on which one or more forces are acting.

    Newton III is applicable where two objects interact with each other. For example:

    • a man pushes a motor car
    • you stand on the floor of your room

    A book lies on a table: The book exerts a downward force, its weight, on the table. The table exerts an equal upward force on the book, i.e. the normalforce (N).

    Non-contact forces

    • A second force pair with the above example: The earth exerts a gravitational pull (Fg)on the book; the book exerts an equal but oppositely directed force Fg, on the earth

      OR

    • A planet(P)is at a distance r from the earth(E) : The earth (E) exerts an attractive force on P, and P exerts an equal but oppositely directed force on E
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    NEWTON'S LAW OF UNIVERSAL GRAVITATION

    • Legend has it that Newton's Law of Universal Gravitation was inspired by his observation of an apple falling from a tree. He realised that the earth itself had to be exerting an attractive force on the apple, accelerating it downwards.
    • Newton called this force gravitational force. Gravitational force has the following properties:
      • lt is an attractive force.
      • lt is a non-contact force and is exerted even if objects do not touch each other.
    • It exists between any two objects with mass in the universe.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • The force exerted by each object on another is of equal magnitude, but opposite in direction. Fm2 on m1 = Fm2 on m1 (Newton III)
    • The magnitude of the gravitational force between objects depends on:
      • the magnitude of their masses
      • the distance between their centres (see the next section)

    Through scientific investigations it has been determined force between objects is:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The value of g

    • The gravitational acceleration (g) on or near the earth thus depends on the mass (M) of the earth and on the distance (d) from its centre.
    • The value of g on or near other planets can be calculated in a similar way by using the mass and radius of the planets.
    • The value of g on/near the different planets varies, and therefore so does the weight of an object. However, the mass of an object is the same everywhere.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • The mass of an object refers to the quantity of matter it contains and it remains constant throughout the universe.
    • It also shows how difficult it is to change the state of rest or motion of an object. lt is therefore a measure of the inertia of an object and is sometimes known as the inertial mass. (As mass increases, so inertia increases).
    • The Sl unit for mass is the kilogram (kg).
    • The weight of an object is the gravitational pull the earth exerts on it. lts value differs on the different planets.
    • The Sl unit for weight is newton (N).
    • An object experiences weightlessness when there is no gravitational field (the gravitational pull on it is zero), e.g. when an astronaut in a spacecraft moves through space.
    • However, it is possible to experience a sense of weightlessness even though you are in a gravitationalfield:
      • The sensation of gravity is caused by the pressure of the upwards force of the floor against you.
      • The apparent weight of a person or object is determined by the normal force exerted by the surface on which they rest.
      • lf the floor gives way under someone, e.g. when an elevator cable breaks, gravity is the only force acting on him. So, a person free falls and experiences weightlessness (the floor of the elevator experiences the same acceleration and does not push up against him).
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    What is momentum?

    Consider two rugby players, masses B0 kg and 120 kg respectively, running at the same velocity v. Which one would be easier to stop and bring down? lf the B0 kg player increases his velocity to 2v, which player would now be easier to stop?

    From experience we know that it is harder to stop the person with the qreater momentum.

    The momentum of an object is the product : of the mass and velocity of the object.

    Therefore:

    momentum = mass x velocity
    P = m x v

    • Momentum is therefore a measure of an object's amount of motion. This shows how difficult it is to bring an object to rest and it depends on its mass and velocity.
    • Therefore the momentum of an object can be increased by increasing its mass or its velocity or both.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Momentum is a vector. The magnitude and direction of the momentum of an object can therefore be represented by a vector diagram, e.g  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Newton's second law can now be described irr [crrrrs of rnomentum.

    ln words:

    • Newton's second law in terms of momentum: The resultant/net force that acts on an object is equal to the rate of change in nromentum of the object in the direction of the resultant/net force.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Velocity and momentum of an object increase in the direction of motion as a result of a net force in the direction of motion:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Velocity and momentum of an object decrease in the direction of motion as a result of a net force in the opposite direction to the motion :

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The Change in the direction of the velocity and momentum of an object is as a result of a net force in the opposite direction from the original motion:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Now the focus is on what happens during the collision so that the momentum of each separate object changes. According to Newton II , if a resultant or net force (Fnet) is applied on an object for a time interval (Δt), the object's momentum will change.

    What is impulse?

    lmpulse is the product of the resultant/net force acting on an object and the time the resultant/net force acts on the object.

    Fnet x Δt

    lmpulse is a vector quantity. The impulse on an object has a magnitude Fnet Δt and has the same direction as the force acting on the object.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • System: A system is a small part of space that we are considering when investigating and solving a particular problem. Everything outside this system is called the environment.
    • lsolated system: An isolated system is a system on which the resultant/net external force is zero. An isolated system excludes external forces that originate outside the system of colliding objects, e.g. friction. Only internalforces are considered, e.g. contact forces between colliding objects.
    • lnternal forces: Forces that objects exert on each other within a system, e.g. contact forces between colliding cars, gravitational force.
    • Externalforces: Forces from outside a system that act on the objects within a system, e.g. applied force, frictionalforce, air resistance, tension in a rope, force on a car or a rocket.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    A collision is considered elastic if the total kinetic energy of the objects in the system during the collision is conserved, i.e. ΣEk initial = ΣEk initial. Otherwise it is an inelastic collision.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    lnformal assessment: Newton's cradle

    A good example of the conservation of momentum and kinetic energy can be demonstrated by Newton's cradle. A number of identical metal balls are suspended from two light strings within a metal frame so that the balls just touch one ' another. The pieces of string are identical and restrict the balls to the same vertical plane.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Method:

    • First pull back one ball and let it drop back.
    • Describe your observation.
    • Now pull back two balls together, and let them drop back.
    • Repeat with three balls.

    Observation:

    As soon as the ball(s) fall back and collide with the remaining balls at rest, they come to a standstill, while the same number of balls at the other end r moves away. They fall back again, collide with the balls at rest, come to a standstill and the first ones move away again. The process is repeated.

    Conclusion:

    • Once each ball has transferred its energy to the system of balls, it comes to rest. An equal number of balls at the opposite end acquires this energy moves away to the other side, reaches the same height, falls back and comes to rest again. i
    • lf we assume that no energy is 'lost' in the form of heat or sound, the process will continue indefinitely.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Introduction

    The earth pulls all objects towards it with a downward gravitational force. This is a force of attraction towards the centre of the earth and is known as the weight of the object. lt is a constant downward force and leads to the constant (uniform) downward acceleration of an object in the air, i.e. gravitational acceleration (g). lf there are no other forces apart from the gravitational force acting on the object, we say that the object is in free fall. An object that is in free fall experiences weightlessness.

    Important terms

    The following terms are important in vertical projectile motion:

    • Gravitational field: This is the space around an object of mass (e.9. the earth) in which another mass experiences a gravitationalforce.
    • Acceleration due to gravity (g): The acceleration of a falling object as a result of the attractive gravitational force of the earth, in the absence of other forces such as air resistance.
    • Free fall: The unhindered movement of an object in the gravitational field of the earth, when only the gravitational force is acting on it.
    • Projectile: An object that is moving through the air, experiencing free fall, after being dropped, thrown or shot. (ln the air, air resistance is small. lf air resistance ls ignored, gravitational force is the only force acting on the object.)
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Examples of projectiles: A rock, ball or bullet that is dropped or thrown vertically ('1-dimensional), projected horizontally or projected at an angle to the ground (2-dimensional).

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    THE BOUNCING BALL

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    ENERGY

    Energy can be transferred from one object to another and is equal to the amount of work done by the transfer.

    There are different forms of energy :

    • electrical energy
    • light energy
    • heat energy
    • chemical energy
    • sound energy
    • mechanical energy

    Mechanicalenergy can be divided into:

    Kinetic energy

    This is the energy an object has due to its motion.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Gravitational potential energy

    This is the energy an object has due to its position/height above the earth.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Kinetic energy and work done

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Work-energy theorem

    From the previous explanation it is clear that if net work is done on an object, then the Ek of the object will change.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Using an equation of motion

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Gravitational potential energy and work done

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Conservative forces

    • Forces acting on an object can be classified as conservative or non-conservative forces.

    A conservative force is a force for which the work done in moving an object between two points is independent of the path taken.

    The closed path test may be used to determine whether a force is a conservative force or not. lf various forces act on an object and it moves from an initial position in a closed path and back again to its initial position, the net work done on the object by a conservative force will be equal to zero, irrespective of the path it followed.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Non-conservative forces

    A conservative force is a force for which the work done in moving an object between two points depends on the the path taken.

    The work done by a non-conservative force is not conserved, but is converted into other forms of energy, e.g. heat or sound energy. Frictional force is an example of a non-conservative force.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Power is the rate at which work is done OR the rate of energy transfer.

    Power in terms of force and velocity

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Pave = FVave

    Power of borehole pumps

    • In certain parts of the wodd and also in many rural areas in South Africa, there is not enough surface water available for human use.
    • Boreholes (narrow shafts) are drilled vertically through one or more impenetrable rock layers in the hope of finding underground water. lf sufficient water is found, the water is pumped to the surface from deep under the ground.
    • Mechanical or electrical pumps can be used for this, and then mechanical or electrical energy is converted into potential and kinetic energy of the water. A mass of water (m) is elevated by a height (h)
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    MATTER AND MATERIALS - CHEMISTRY

    WHAT IS ORGANIC CHEMISTRY?

    The origins of organic compounds

    • Organic chemistry originally referred to the chemistry of compounds found in living organisms, i.e. in plants, animals and the human body. These compounds mainly consist of the element carbon, derived from CO2 gas in the atmosphere.
    • During the process of photosynthesis in green plants, CO2, radiant energy and water are transformed into simple carbohydrates that join to form chains. Animals eat plants and, in turn, change the carbohydrates into other carbon chains and large macromolecules, e.g" proteins, oils and fats.
    • When people and animals respire, COz is exhaled and returned to the atmosphere. Dead animals and decomposing plants also release COz. ln this way the COz is recycled back into the atmosphere through the earth's soil, water and living organisms, including humans.
    • Millions of years ago, large quantities of plant and animal materials were covered in mud. As a result of high pressure and temperature, the dead plant and animal material was converted into natural gas, oil and coal, also known as fossil fuels. These are good sources of carbon and today they are mainly used as fuels. (When they burn, COz gas is released back into the atmosphere.)
    • Over time, chemists have succeeded in making the organic compound, urea, from inorganic substances. Although the compound was prepared synthetically, the chemical composition was the same as the urea found in nature.
    • Subsequently a large variety of carbon compounds have been made from the carbon chain molecules in coal, oils and gases, e.g. plastics, paints, glues, fertilisers, medicines and many more. These compounds have no connection with living organisms, but are referred to as organic compounds.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Today organic chemistry is the largest branch of chemistry. There are already millions of organic compounds in existence and the number increases daily.

      Therefore:

      • Organic chemistry now refers to the chemistry of carbon compounds. This excludes compounds such as COz, CO, COz2- (carbonates)and CN- (cyanides).
    • Carbon is a non-metal element found in group 4 of the periodic table. I It has the electron structure 6C) 1s2 2s2 2p2 and thus has four valence electrons. By sharing electron pairs, it can form a maximum of four I covalent bonds with other atoms.
    • Carbon atoms can bond with each other in long simplechain structures; rings or additional branches can form too, i.e. carbon-carbon linkage takes place.
    • C atoms form bonds with other C atoms by way of single, double or triple covalent bonds. (Relatively high bond energies are involved, making long molecular chains possible.
    • A carbon atom can also form covalent bonds with other atoms, e.g. hydrogen (H), oxygen (O), nitrogen (N) and the halogens (F, C0, Br, l).
    • The four single bonds around a central C atom are positioned in space according to the 4 angles of a tetrahedron (bond angles = 109,5o) in order to maximise the distance between them.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES

    Compounds are classified into families called homologous series according to a characteristic group in the compound, the functional group. The functional group indicates the position in the molecule where a chemical reaction with other

    A functional group is a type of bond, atom or group of atoms in a molecule that determines the physical and chemical properties of group of organic compounds.

    A homologous series is a group of compounds containing the same functional group and can thus be described by the same general formula.

    Some homologous series and their corresponding functional groups

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Saturated and unsaturated bonds

    Hydrocarbons: Carbon compounds consisting of hydrogen and carbon atoms only.

    Saturated: Compounds in which there are no multiple bonds between C atoms in their hydrocarbon chains.

    Unsaturated: Compounds with one or more multiple bonds between C atoms in their hydrocarbon chains.

    • In saturated hydrocarbons each C atom bonds with a maximum of 4 other atoms. They are very stable and do not react easily.
    • In unsaturated hydrocarbons, the double or triple bonds can be broken and more atoms can bond with the molecule.
    • The stem (root) name of the different hydrocarbons and members of the other homologous series is determined by the number of C atoms in the longest continuous chain/ring
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Alkanes

    Structure

    • The alkanes are the simplest homologous series consisting only of C atoms and H atoms.
    • Alkanes are saturated hydrocarbons with only single covalent bonds between C atoms.
    • The general formula of the alkanes is CnHzn + 2.
    • The suffix of the alkanes is -ane.
    • The first B alkanes are:  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • The structural formula of the first four alkanes is:  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The alkanes with a simple chain structure are referred to as normal alkanes, or n-alkanes:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Structure

    • Alkenes and alkynes are unsaturated hydrocarbons. Alkenes have at least one double bond (=) and alkynes at least one triple bond (=) in their structure.
    • The double or triple bond forms the functional group. These bonds are electron rich, so they are the position in the compound where a reaction with other substances can take place. During the reaction, the bond breaks and more atoms can attach to the molecule to form a more saturated product.

    Alkenes

    • The general formula of the alkenes is CnH2n.
    • The suffix of the alkenes is -ene.
    • The first seven alkenes are :  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Alkynes

    • The general formula of the alkynes is CnHzn - z.
    • The suffix of the alkynes is -yne.
    • The first seven alkynes are:  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • The structural formulae, condensed structural formulae and spatial structures of the first three alkenes and alkynes follow.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Production and a few uses

    • Alkenes, e.g. ethene or propene are formed during the cracking of petroleum.
    • Ethene is the simplest alkene and is used for the industrial preparation of ethanol, ethanal and chloroethane, which are used as raw materials for the preparation of many other organic compounds.
    • Furthermore, ethene has two other very important uses:
      • lt is an ingredient found naturally in plants and stimulates the ripening of fruit. Therefore, it is also widely used in the controlled ripening of fruit.
      • lt is a very important raw material used for the manufacturing of plastics. Through the polymerisation of ethene, plastics such as polyethene, polyvinylchloride (PVC), as well as polystyrene can be manufactured.
    • Propene is also polymerised on a large scale and used in the manufacturing of polypropylene and other plastics.
    • Ethyne (acetylene) is the simplest alkyne and is especially known for its use in oxy-acetylene blow torches. Temperatures of over 3 000oC are reached during the highly exothermic combustion reaction of ethyne with pure oxygen. This extreme heat is used for the welding of metals.

    Structure

    • These compounds are alkanes in which one or more of the hydrogen atoms have been replaced by a halogen atom (X = F, C0, Br, l).
    • The general formula is CnH2n + 1 'X (or R - X for short; R = alkyl group)
    • Haloalkanes are generally volatile liquids that do not dissolve in water.
    • Some of the simplest haloalkanes:  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    lntroduction

    Alcohols are probably one of the most commonly used organic compounds with a great number of possible uses. They can be used as raw materials in the preparation of almost any compound, e.g. alkyl halides, alkenes, aldehydes, ketones, esters, acids and many more. They are also used as solvents for other organic compounds. Alcohols are used increasingly as fuels in vehicles, but the compound ethanol ls probably the most popular by far because of its use in alcoholic beverages.

    Structure

    • The alcohols are a group of compounds containing one or more hydroxyl (-OH)group.
    • The general formula is CnH2n + OH or R - OH for short. The suffix of alcohols is -ol.
    • Alcohols are polar molecules and can form intermolecular bonds with water molecules by means of hydrogen bonding so that the smaller alcohols (number of C atoms < 4) readily dissolve in water.
    • There are also strong hydrogen bonds between the OH sections of the alcohol molecules. Therefore, the alcohols have higher boiling and melting points than ordinary hydrocarbons of corresponding size.

    The first three alcohols are:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    More than one OH group on the main chain:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Production and uses (ethanol)

    Alcohols are prepared industrially by the addition of water to alkenes (hydration). Ethanol is thus prepared by the addition of HzO to ethene, i.e.

    It is also a byproduct of the preparation of petrol and oils from coal by SASOL (Fischer-Tropsch synthesis).

    Ethanol can also be prepared by the natural fermentation of sugars and carbohydrates in fruit and other crops (e.9. wheat, maize) i.e.

    Primary, secondary and tertiary alcohols

    Alcohols are divided into three groups according to the number of C atoms that are bonded to the C atom with the hydroxyl group (-OH) OR

    The C atom with the OH group is classified as a primary, secondary or tertiary carbon atom, and accordingly the alcohol is classified as primary, secondary or tertiary.

    A primary C atom is bonded to only one other C atom.

    A secondary C atom is bonded to two other C atoms.

    A tertiary C atom is bonded to three other C atoms, e.g.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Structure

    • Aldehydes are compounds containing a formyl group (carbonyl group with at least 1 H atom on the same C atom).
    • The general formula for aldehydes is CnH2nO.
    • The suffix of the aldehydes is -al.
    • Aldehydes are formed during the oxidation of alcohols.
    • The first three aldehydes are :  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Structure

    • The functional group is the carboxyl group -COOH (carboxyl = carbonyl + hydroxyl).
    • The general formula is CnH2nO2
    • Carboxylic acids have the suffix -oic acid.
    • Carboxylic acids are commonly found in nature and are organic acids, hence the name'carboxylic acid'.
    • Carboxylic acids can be prepared in various ways. One method is by the oxidation of an aldehyde by a strong oxidising agent

    They are not very strong acids, e.g.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Esters have pleasant smells and play a large role in the food and cosmetics industries. The esters responsible for the fruity flavours and aromas in milkshakes, perfumes and other sprays (e.9. car deodorisers) are chemically prepared without any natural substances, e.g.

    ethyl methanoate = strawberry flavour
    butyl butanoate = pineapple flavour

    Preparation

    Esters are formed from carboxylic acids and contain a carboxyl group in which the H atom of the OH group has been substituted byan alkylgroup, i.e.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    ISOMERS

    ISOMERS are organic compounds that have the same molecular formulae, but different structural formulae (arrangement of atoms).

    We differentiate between different kinds of structural isomers: Chain isomers, positional isomers and functional isomers.

    Chain isomers are molecules with the same molecular formulae, but different types of chains.

    For instance, one long chain or branched structures as follows:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Similarities and differences

    • All three compounds have 5 C atoms and 12 H atoms and have the same molecular formula, CsH12.
    • They all belong to the same homologous series, the alkanes.
    • They have different structural formulae: A: alkanes: straight chain structure
      B and C: alkanes: branched structures with 1 and 2 alkyl groups respectively r They have different names as indicated.
    • They differ in terms of physical properties, e.g. melting and boiling points.

    Positional isomers are molecules with the same molecular formula, but with substituents or functional groups in different positions on the parent chain.

    A halogen atom or another functional group, e.g. a double bond, can occur in two possible positions on the 4C main chain.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Please note that the number of the C atom to which the functional group and substituents are attached is indicated in the name and is used to distinguish between the positional isomers. (See nomenclature rules alongside.)

    Similarities and differences

    • The two compounds in both examples have the same molecular formula.
    • They have the same functional group and belong to the same homologous series, i.e. (1) the haloalkanes/alkylhalides and (2) alkenes.
    • Their names differ as shown.
    • They have different physical properties.

    Functional isomers are molecules with the same molecular formula, but with different functional groups and therefore belong to different homologous series.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Similarities and differences

    • Both have the same molecular formula C3H6O2.
    • They have different structural formulae and belong to different homologous series.
      A: carboxylic acids
      B: esters
    • They have completely different physical and chemical properties.
    • Aldehydes and ketones (general formula CnHznO) with the same number of C atoms are functional isomers.
    • Carboxylic acids and esters (general formula CnHznOz) with the same number of C atoms are functional isomers.

    NOMENGLATURE RULES FOR HYDROGARBONS

    The IUPAC (lnternational Union of Pure and Applied Chemistry) system uses the following method to determine the names of organic compounds. We thus refer to the IUPAC name or systematic name of the compound. This system uses 3 parts, i.e. a stem, prefix and suffix, to form the name.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Step

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Chain structures

    • The name ends with '-ane', 'ene' or'-yne'.
    • Number the longest C chain from the side closest to the double (:) or triple (=) bond in alkenes/alkynes or from the side closest to the first side chain/branch (in alkanes).
    • The position of the double/triple bond is indicated between the stem name and the suffix.
    • The substituents (together with their positions) are placed in front of the stem in alphabetical order.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Alkenes with more than one double bond

    • Dienes (2 double bonds) and trienes (3 double bonds)
    • These compounds have the suffixes'diene' or'triene' in their names: name = stem + diene or triene e.g. butadiene
    • The chain is numbered from the end nearest the first':' bond. The positions of both ':' must have the smallest number possible.
    • Structures with alternate single and double bonds are called conjugated dienes or trienes.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The halogen atom or atoms are regarded as substituents and the main chain is numbered from the end nearest to the first substituent, regardless of whether it is a halogen or alkyl group.

    If two or three identical halogen substituents are present, 'di-' or'16i-' precedes the prefix. The prefix is written along with other substituents in alphabetical order before the stem name.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Alcohols

    • The OH group is the main functional group and the main chain must contain the C atom with the OH group.
    • The OH group has precedence over alkyl groups and the main chain is thus numbered from the terminal C atom nearest to the OH group.
    • The position of the OH group must be indicated by a number in the name.
    • The stem and prefixes are determined as for the alkanes, but the name ends in -ol.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Aldehydes

    • The name ends in _al
    • The main/parent chain must contain the formyl group and numbering starts at the formyl group.
    • Substituents along with their positions precede the stem in alphabetical order.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Ketones

    • The name ends in -one.
    • The main chain must contain the carbonyl group
    • Start numbering from the side closest to the carbonyl group. lndicate the number of the C atom with the carbonyl group between the stem name and the suffix.
    • Substituents, together with their positions, precede the stem in alphabetical order.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Carboxylic acids

    • The name ends in -oic acid
    • The main chain must contain the carboxyl grou
    • Start numbering from the carboxyl group.
    • Substituents, together with their positions, precede the chain in alphabetical order.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Esters

    • The name ends in -oate.
    • The stem of the alcohol with the suffix Lyl' forms the first part of the name.
    • The stem of the carboxylic acid with 'oate' forms the second part of the name, e.g.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • The two parts of the name are separate words (this series only).
    • Method of identifying the compound from the structural formula:
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    PHYSIGAL PROPERTIES OF THE DIFFERENT HOMOLOGOUS SERIES

    Physical properties of chemical compounds include the following:

    • Phase: The gas, liquid or solid state of the compound at room temperature.
    • Boiling point: The temperature at which the vapour pressure of a substance is equal to atmospheric pressure.
    • Melting point: The temperature at which the solid and liquid phases of a substance are in equilibrium.
    • Volatility: How easily a liquid changes into a gas.
    • Vapour pressure: The pressure exerted by a vapour at equilibrium with its solid or liquid phases at a given temperature in a closed system.
    • Solubility: How easily a substance dissolves in non-polar solvents (e.9. CCla) or in polar solvents (e.g. H2O).

      The physical properties of compounds reflect the strength of the intermolecular forces, i.e. the attraction between molecules.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Non-polar molecules have non-polar bonds between atoms or they are symmetrical molecules in which the net dipole moment is zero, i.e. there is an even distribution of charge.

    Alkane molecules are non-polar molecules. When two alkane molecules are near each other, attraction and repulsion between their nuclei and electron clouds can result in an uneven distribution of the charge in the molecules. Temporary dipoles are induced in the molecules (one pole d+ and the other d-). Through a chain effect, temporary dipoles are induced in adjacent molecules. This results in weak forces of attraction, known as Van der Waals dispersion forces, between the molecules.

    When atoms of different electronegativities bond, asymmetric, polar covalent bonds form between them (0 . Eneg difference .2). lf this molecule is asymmetrical, there will be an uneven distribution of charge in the molecule and a net dipole moment > 0. This results in polar molecules with two different poles that are called permanent dipoles. Forces of attraction form between the opposite poles of different polar molecules that are referred to as Van der Waals dipole-dipole forces. These forces are stronger than the Van der Waals dispersion forces.

    Hydrogen bonds form between molecules with O-H, N-H or F-H bonds, i.e. between the H atom of one molecule and an O, N or F atom of an adjacent molecule.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Factors determining the physical properties of organic compounds include:

    • type (and strength) of the intermolecular forces
    • molecular size/chain length
    • amount of branching
    • number of similar functional groups.

      During practical investigations of the physical properties such as boiling points, any one of these factors is taken as the independent variable and the others are kept constant.

      Types of intermolecular forces

      The stronger the intermolecular forces (e.9. hydrogen bonds are stronger than Van der Waals dispersion forces), the more energy needed to overcome the forces and therefore:

      • the higher the boiling and melting points
      • the higher the viscosity
      • the lower the vapour pressure.

      Compare the intermolecular forces of different homologous serie

      The following table compares the (1) boiling and melting points as well as (2) the solubility in HzO of molecules from different homologous series, but with corresponding molecular masses:

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      A comparison between the boiling points of different homologous series with the same number of C atoms

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Comparison of boiling points and solubility in HzO of a few compounds from different homologous series, but with the same molecular mass:

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Physical properties of ethane, *dimethylether, chloroethane, ethanol and ethanoic acid

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Ethane

      Ethane consists of non-polar molecules with only Van der Waals dispersion forces between the molecules. Consequently, it has a very low boiling point, i.e. -B9oC. Because of the low boiling point it has a high vapour pressure. Therefore, ethane is a gas at room temperature. lt is colourless, odourless and insoluble in water.

      Dimethylether

      Contains a CO bond that is slightly polar, but the molecules are symmetrical and therefore non-polar as a whole. The O atom between the methyl groups makes the chain longer, so that there are stronger Van der Waals dispersion forces between adjacent molecules than between two ethane molecules. lt has a higher boiling point than that of ether, i.e. -24,8oC, and is a colourless gas at room temperature. lt is also insoluble in water.

      Chloroethane

      Chloroethane molecules have a large chlorine atom in the place of one of the H atoms of ethane. Therefore chloroethane consists of polar molecules with Van der Waals dipole-dipole forces (in addition to dispersion forces) between the molecules. Consequently, the boiling point of chloroethane is higher than that of ethane and dimethylether, i.e. 12oC. Chloroethane is a colourless gas at room temperature, is highly flammable and has a strong odour. It is almost insoluble in water.

      Ethanol

      Ethanol molecules contain an OH group attached to the carbon chain and can therefore form strong hydrogen bonds with adjacent molecules. Consequently, more energy is required to overcome the forces between the molecules, so ethanol has a much higher boiling point of 78oC. Ethanol is a colourless liquid, very volatile and highly flammable. lt is soluble in water.

      Ethanoic

      Ethanoic acid molecules contain an O atom as well as an OH group and can therefore form two H bonds with adjacent molecules. Consequently, the boiling point of ethanoic acid is considerably higher than that of the other compounds mentioned above. Ethanoic acid (acetic acid) is a colourless liquid with a distinct sour smell. lt is soluble in water.

      Size of molecules / Chain length

      The longer the C chains, i.e. the more C atoms in a compound, the greater the molecular mass and the stronger the Van der Waals forces between the molecules. The stronger these forces, the more energy is needed to overcome the forces and:

      • the higher the boiling and melting points
      • the higher the viscosity
      • the lower the vapour pressure.

      The boiling and melting points of compounds from the same homologous series compare as follows:

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Melting and boiling points of straight-chained alkanes (n-alkanes)

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Melting and boiling points of the alkenes

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Degree of branching

      The more branched a compound is, the more spherical its structure and so its contact surface area is smaller, thus the weaker the Van der Waals forces between the molecules and:

      • the lower the boiling and melting points
      • the higher the vapour pressure.

      The boiling points of the three structural isomers of pentane (c5H12) are as follows:

       You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

      Alcohols with branched alkyl groups are more soluble in water than straight chain structures with the same number of C atoms.

      Number of functional groups of the same kind

      The more halogens (Cl, Br, l), OH groups, or CO or CHO or COOH groups, the higher the melting and boiling points and the lower the vapour pressure.

    APPLIGATIONS OF ORGANIG CHEMISTRY

    Two applications of organic chemistry are combustion reactions to release energy and the preparation of esters which are used as flavouring.

    Alkanes, alkenes, alkynes and alcohols burn easily in oxygen, and in the process release large quantities of energy in highly exothermic reactions.

    Alkanes

    Alkanes are our most important (fossil) fuels and the main source of various kinds of energy such as heat energy, energy for powering cars, the generation of electricity, etc.

    Alkanes will burn in oxygen (air) to form water and carbon dioxide (COz), where oxygen is in excess, or carbon monoxide (CO), where oxygen is the limiting reagent.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Additional information (optional)

    The functioning of a petrol engine: ln the carburettor and the distributor, the fuel is converted into a vapour (gas) and mixed with air (Oz). The gas mixture is then compressed in the cylinder and a spark from the spark plugs ignites it. Combustion (as set out above) takes place. The spark provides the activation energy. A diesel engine does not use spark plugs but functions by means of spontaneous combustion at a specific temperature and pressure.

    The antiknock tendency of a fuel: is its resistance to spontaneous combustion (without a spark) at high temperature and pressure and is indicated by its octane number. Heptane has an octane number of . 0 (it easily undergoes spontaneous combustion) and 2,2,4-trimethylpentane (isooctane) has an octane number of 100. 95 octane petrol is 95% as effective as the pure octane isomer and corresponds to a mixture containing 95% 2,2,4-lrimelhylpentane and 5% heptane.

    Alkynes

    Ethyne (acetylene) is used extensively for welding metals with an oxy-acetylene torch.

    2CzHz+5Os - 4CO2+2H2O + energy

    This reaction can reach temperatures of up to 2 500"C using air.

    Esterification

    Another area where organic chemistry has wide application is in the preparation of esters. An ester can be prepared from the reaction between an alcohol and a carboxylic acid in the presence of a strong acid.

    Apart from the combustion and esterification reactions, we also need to study the following three kinds of chemical reactions in organic compounds: addition, substitution and elimination"

    Addition reactions

    There are different types of addition reactions: hydrohalogenation, halogenation, hydration and hydrogenation.

    Hydrohalogenation

    • Addition of a hydrogen halide (H-X), e.g. HC0, HBr or Hl, to an alkene.
    • A haloalkane forms as product.
    • The double bond between the two C atoms breaks, and the H atom and halogen atom attach to the C atoms on either side.
    • Markovnikov's rule ln compounds where the double bond is asymmetrically placed in the molecule, the major product is formed by the addition of the H atom to the C atom that already has the most H atoms, and the addition of the halogen atom to the C atom with the most alkyl substituents. (See example 2.)
    • Reaction conditions: Water-free H-X is used. No water must be present. This is to prevent bonding with an OH group
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    lf the C atoms with the double bond have the same number of H atoms and alkyl substituents, a mixture of possible products is formed, e.g.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Halogenation

    • Addition of a halogen (X2), e.g. F2, Cl2, Br2,12, to an alkene.
    • A haloalkane forms as product.
    • The double bond between two C atoms breaks and a halogen atom attaches to each of the C atoms.
    • Reaction conditions: spontaneous
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Hydration

    • Addition of waterto an alkene.
    • The double bond between the two C atoms breaks, and an H atom and an OH group attach to the C atoms on either side.
    • This reaction is used for the industrial preparation of alcohols.
    • Markovnikov's rule is also applicable here, i.e. the major product forms by the addition of an H atom to the C atom at the '=' with the most H atoms, and the addition of OH to the C atom with the most alkyl groups.
    • Reaction conditions: An excess of water and a strong acid such as sulphuric acid (H2SO4) or phosphoric acid (H3PO4) as catalyst.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Hydrogenation

    • Addition of hydrogen to an alkene.
    • A saturated alkane forms as product.
    • Reaction conditions: Alkene dissolved in a non-polar solvent in a H2 atmosphere, with a Pt, Pd or Ni catalyst. (The catalyst provides a surface where the reaction can take place and decreases the activation energy of the reaction.)
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Saturated compounds such as alkanes, haloalkanes and alcohols, can undergo an elimination reaction to form an unsaturated alkene.

    There are different kinds of elimination reactions: dehydrohalogenation, dehydration and cracking of molecules"

    Dehydrohalogenation

    • When the halide atom (e.9. Cl,, Br, etc.)is removed togetherwith an H atom of an adjacent C atom from a haloalkane, an elimination reaction occurs (an H-X is removed).
    • An alkene forms as product.
    • Zaitzev's rule of elimination: If more than one elimination product is possible, the major product is formed when the H atom is lost from the C atom already with the least number of H atoms.
      OR The major product is the alkene with the highest substituted double bond (the least H atoms and the most alkyl groups on the C atoms of the double bond).

    Reaction conditions:

    1) Use a concentrated solution of NaOH or KOH in pure ethanol as solvent, i.e. warm ethanolic NaOH/KOH.

    2) Heat is applied under reflux (gases condensate and return to the reaction mixture during heating).

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Dehydration

    • The elimination reaction where water (H2O) is eliminated from an alcohol, is known as dehydration.
    • This is the reverse reaction of the hydration addition reaction during which H2O is added to an alkene to form an alcohol.
    • The reaction involves the elimination of the -OH group together with an H atom of an adjacent C atom when the alcohol is heated together with a strong acid.
    • The reaction cannot take place with methanol (CH3OH) as it has only one C atom, i.e. there is no adjacent C atom that can release a H atom.
    • Zaitzev's rule is applied again: lf more than one elimination product is possible, the major product is the one formed where the H atom is removed from the C atom with the least H atoms.
    • Reaction conditions: Heat the alcohol together with an excess of concentrated H2SO4 (sulphuric acid) or H2S4 (phosphoric acid).
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Cracking of hydrocarbons

    Natural crude oil consists of long C chains with high molecular masses and high boiling points, making it less useful in the fuel industry. The longer alkane chains can be broken up into more useful, shorter carbon chains (smaller molecules), with smaller molecular masses by a process called cracking. Shorter chains burn more evenly and easily.

    • The products are:
      • an alkane as well as an alkene(s)with shorter C chains )
      • one or more alkenes + H2(g)
    • Cracking can occur under the following reaction conditions: > Thermal cracking: under high pressure and at high temperatures without a catalyst r Catalytic cracking: at lower temperatures with a catalyst, e.g. Pt
    • The smaller molecules of the 'cracked' vapours are separated from one other by fractional distillation.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Substitution reactions take place when an atom or a group of atoms in a molecule is replaced by another atom or group of atoms.

    Halogenation of alkanes

    • Alkanes are not very reactive because:
      • the -C-C- and -C-H bonds are fairly strong and stable
      • their molecules are non-polar and they do not readily react with other polar molecules such as water, acids, bases, etc.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Reaction of an alkane vs an alkene with bromine water

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • Many of the carbon compounds present in living organisms, such as carbohydrates, proteins and DNA molecules, are examples of biological macromolecules or polymers. Rubber is an example of a natural polymer extracted from rubber trees.
    • ln the past century, scientists have also prepared a large variety of synthetic polymers. Many of these substances form part of the plastics industry and are manufactured from the carbon compounds of fossil fuels.

    Terminology

    Macromolecules are molecules consisting of a large number of atoms (hundreds and even thousands of atoms can bond to form macromolecules).

    Polymers are large molecules composed of smaller monomer units covalently bonded to each other in a repeating pattern.

    Monomers are small, organic molecules that can be covalently bonded to each other in a repeating pattern.

    When a polymer consists of one kind of monomer, it is called a homopolymer. When it consists of more than one kind of monomer, it is called a copolymer.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The physical properties of the macromolecules differ considerably from the smaller monomers. The factors determining their physical properties include intermolecular forces, chain length and cross-linking.

    They do, however, show corresponding chemical properties and may undergo addition, substitution, acid-base and other reactions.

    There are two types of polymers:

    Thermoplastic polymers

    • These polymers consist of long, thin chains braided together. There are weak Van der Waals forces between the chains.
    • The individual chains can easily move over each other when heated or stretched.

    Thermosetting polymers

    • These plastics contain a network of large molecules with cross-linking between them.
    • The molecules cannot easily move over each other.

    General properties

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Preparation of a polymer

    Polymerisation is a chemical reaction in which monomer molecules join to form a polymer.

    The process can take place by way of addition or elimination reactions. A large number of monomers can attach to each other, by addition, to form long chains.

    Addition polymers

    Addition polymerisation: A reaction in which small molecules join to form very large molecules by the additional of double bonds.

    Addition polymer: A polymer formed when monomers (usually containing a double bond) combine through an addition reaction.

    • One of the chemical reactions studied is the addition reaction occurring in alkenes, during which the double bond between two carbon atoms breaks and two other atoms attach to either side of the bond.
    • Alkenes can polymerise by means of addition reactions. When the C=C double bond in an alkene molecule breaks, they can attach to each other by an addition reaction to form a long, straight chain with C-C single bonds. The electrons in the double bond are used to attach the monomers so that no atoms need to be eliminated.
    • A large molecule with repeating units is formed. These units coincide with the attached monomers and are used to differentiate between different polymers.

    Polythene

    • Ethene is an example of a simple monomer. Polyethene (polythene for short or polyethylene in the industry) is formed when ethene molecules attach to each other with a repeating unit
    • This polymerisation takes place very rapidly so that thousands of ethene units may attach to each other within a second.

    Other addition polymers

    Monomers can contain different groups of atoms or functional groups, attached to the C atoms. ln this way polymers can be distinguished from one another.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Low density polyethylene (LDPE)

    General properties:

    • Chemically non-reactive (does not react with acids, bases or alcohols, and not readily with ketones, aldehydes or esters, but does react with halogens)
    • Water resistant
    • Electrical insulator
    • Lightweight but strong
    • Relatively soft and flexible
    • Translucent

    General uses:

    • ldeal for squeeze bottles because of flexibility
    • Packaging material, e.g. elastic/stretchy film for covering palettes
    • Plastic bags for milk, cheese, meat and other fresh and frozen products
    • Water pipes
    • Telephone and electric cables > Toys and much more

    High density polyethylene (HDPE)

    General properties:

    • Contains long molecular chains with few branches
    • High density (densely packed chains) and lower melting point than LDPE
    • Strong and inflexible
    • High tensile strength

    General uses:

    • Bottles for milk and fruit juices
    • Containers, e.g. for domestic cleaning agents Bottles for shampoo and other hair and skincare products
    • Storage containers for food
    • Plastic crates, tanks, pipes and many more

    Condensation polymerisation: Molecules of two monomers with different functional groups undergo condensation reactions with the loss of small molecules, usually water.

    Condensation polymer: A polymer formed by two monomers with different functional groups that are linked together in a condensation reaction in which a small molecule, usually water, is lost.

    Polyester (PET)

    • Scientists made a major breakthrough when synthetic fibres such as nylon and polyester were manufactured by condensation polymerisation.
    • The formation of a polyester is similar to the synthesis of a simple ester. The difference is just that both the alcohol and carboxylic acid that react with each other have a functional group at both ends of the molecule, e.g.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • When two different monomers with a functional group at both ends of their molecules react in this way, condensation polymerisation takes place and a polyester is formed. A good example is the formation of polyethylene terephthalate from ethane-1,2-diol and benzene-1,4-dicarboxylic acid. See the following example:
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Polylactic acid (PLA)

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Identification of monomers and polymers

    Consider the attached table of a few well-known polymers. You must be able to identify the following :

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Properties of plastic

    The plastics industry has progressed in leaps and bounds over the past few decades and new synthetic materials are being developed all the time and used to make all kinds of useful equipment. Plastic consists of macromolecules formed by the polymerisation of carbon compounds and has the following important properties:

    • Plastic substances are fairly light, cheap to manufacture and very versatile. They are being used more and more to replace other materials such as glass, paper, wood and metal.
    • The molecules contain long chains and for that reason there are strong intermolecular forces between the molecules. The stronger the intermolecular forces, the harder it is to separate the molecules and the stronger the substance. Consequently, plastics are relatively strong, especially those with cross-links between the molecules.
    • Plastics are also non-reactive and do not react with oxygen, water or other chemicals. Consequently, they are resistant lo corrosion. Plastics are also not biodegradable by microorganisms.
    • Plastics are not conductors of electricity or heat because they consist of molecules and do not have moving charges.
    • Plastics can be divided into different groups according to their physical properties such as appearance, flexibility and strength.
    • The manufacturing of disposable products such as baby nappies, packaging materials (especially food packaging) and many other convenience articles has increased sharply over the past few decades.
    • Many of these products are made from plastic, which in turn comes from petroleum, a non-renewable energy source. The depletion of petroleum resources is already causing great concern.
    • Dumping sites are being taken over by tons of plastic waste. This contributes to large-scale pollution of the environment and particularly of water resources.
    • Some substances can be recycled more easily than others. Different methods as well as conditions such as specific temperatures are used to recycle different types of plastic.
    • Therefore, for the recycling of plastic it is necessary to identify and sort the different types of plastic. An international identification system has been introduced for packaging materials. According to this system, plastics are divided into seven groups, and packaging materials are stamped with the correct logo (numbers 1-7 as shown below)during the casting process.
    • The use of thermoplastic soft-drink bottles made of PET instead of tins or glass bottles has increased dramatically due to the various advantages it offers. lt is safe, lightweight and cheaper to transport. lt can be melted and remoulded at relatively low temperatures. The most popular items for recycling are PET, HDPE and PS. The demand for the others is not very high and the recycling is not economical.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    MATTER AND MATERIALS - PHYSIGS

    TRANSMISSION OF ELEGTROMAGNETIC RADIATION

    Electromagnetic spectrum

    Consider the electromagnetic (EM) spectrum from radio waves to gamma rays that was covered in Grade 10:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • The dual particle-wave nature of light combines these two theories,
    • We will investigate the particle nature of EM radiation in this module, as illustrated by the photoelectric effect.
    • Visible light (also called white light) forms part of the electromagnetic spectrum and can be separated into seven colours of light, each with its own frequency.
    • The main sources of visible light are the sun and electric bulbs.
    • Objects become visible when incident light (light that falls on an object) is reflected from the object to the eyes.
    • The frequency of the light that is reflected from the object to your eyes determines the colour observed.
    • Ultraviolet light occurs in the part of the EM spectrum where the frequencies are just higher than that of visible light. The main sources of UV light rays are the sun and fluorescent lamps.

    PHOTOELECTRIC EFFECT

    The photoelectric effect is the process whereby electrons are emitted from a metal surface when light or EM radiation of a suitable frequency is incident on that surface.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The threshold freeuency of a metal is the minimum frequency .,, of light needed to emit electrons from the surface of a metal.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Wave nature

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Electromagnetic radiation is transmitted/propagated through space as waves. When charges are accelerated, repeated induction of magnetic and electrical fields takes place, the strength of which increases and decreases cyclically. An oscillating electromagnetic wave is produced and propagated through space in a direction perpendicular to the magnetic and electricalfields.

    Electromagnetic radiation displays the properties of waves as it demonstrates reflection, refraction, diffraction and interference.

    The observation of diffraction and interference in electromagnetic radiation provides evidence of its wave nature.

    Electromagnetic radiation transfers energy from one point to another. Radiation behaves as if it consists of tiny packets of energy (photons). The photons of a particular radiation contain a fixed amount of energy, E = h/.

    If photons have sufficient energy (have a high enough frequency), they can emit electrons from the surface of a metal.

    This phenomenon, the photoelectric effect, provides evidence for the particle nature of electromagnetic radiation.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    ATOMIC SPEGTRA

    We already know that white light is scattered and split up into its seven constituent colours (dispersed)when it passes through a triangular prism. A band of colours is formed, where one colour flows continuously into the next. This is called a continuous spectrum.

    An atomic emission spectrum is formed when certain frequencies of electromagnetic radiation are emitted due to an atom's electrons making a transition from a higher energy state to a lower energy state.

    Energy transition: An electron (e-) is excited to an unstable, higher energy level and then falls back to a lower level. Photons with a specific energy and ff (or /L)are emitted.

    There are two types of emission spectra:

    • Continuous spectra
    • Line-emission spectra

    Continuous spectra

    • Continuous spectra are observed when light from a glowing solid-state material such as a filament is viewed through a triangular prism.
    • In such dense substances, the atoms are so close together that many different energy transitions of electrons are possible and light photons of any wavelength could be radiated.

    Line-emission spectra

    • A line emission spectrum is observed when a glowing gas, e.g. H2(g) in a gas discharge tube, is observed through a diffraction grating.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The production of !ine-emission spectra

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    An atomic absorption spectrum forms when certain frequencies of electromagnetic radiation that passes through a medium, e.g, a cold gas, is absorbed.

    • When white light (observed through a prism)travels through a cold diluted gas, a continuous spectrum with a number of dark lines (missing frequencies) are visible.
    • When light passes through a cold gas, the gas atoms will absorb photons of specific frequencies in order to excite electrons to higher energy levels.
    • The energy transition of the electrons:
      • depends on the frequency of the absorbed photons.
      • corresponds to the frequency of the missing lines or dark bands in the continuous spectrum.
    • When the electrons return to lower energy levels, the energy is emitted in all directions, but not in the original direction.
    • Each element has its own characteristic absorption spectrum. This spectrum can be used to identify the element. For example, if white light is passed through cold Hz gas, a continuous spectrum with dark lines (missing frequencies) is produced that corresponds exactly with the coloured lines in its line emission spectrum.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Differences between atomic emission and absorption spectra

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Composition of stars and star systems

    • We can use absorption spectra to determine the composition of gases occurring on the surface of stars.
    • Underneath the cooler gases in the outer layers of stars, warmer gases occur The atoms of the cooler gases absorb light photons from the warmer gases and thus the star produces an absorption spectrum.
    • The missing frequencies and corresponding wavelengths of the absorption spectra can be used to identify the elements occurring in the gases. Thus the composition of stars and star systems can be determined.

    Origin of star systems

    The large SKA (Square Kilometre Array) project jointly launched by South Africa and Australia will enable astronomers to go back in time to find out more about the origin and development of stars and star systems.

    • Light rays from very distant stars and star systems take a very long time to travel through space to our telescopes.
    • Astronomers aim to build the most powerfultelescope ever, which will enable them to 'look back' to before the formation of the first stars and star systems.
    • They plan to use radio telescopes with very large antennas, connected by optic fibres. lnformation will be gathered by forming images of the radio waves, instead of using light waves.
    • It is estimated that the antennas will cover an area of approximately 1 km2
    WAVES, SOUND AND LIGHT

    Vibrating objects such as musical instruments and vocal cords produce sound waves. When a person speaks, the vibrations of the vocal cords produce a sound wave. These waves are transmitted by compressions and rarefactions of air, or particles of another medium, to the listener's ear. The further the sound waves move from the source, the weaker they become and the softer the sound we hear

    IMPORTANT TERMS

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    THE DOPPLER EFFEGT (Not for IEB Only CAPS)

    The Doppler effect is the change in frequency (and thus pitch) of the sound that is detected by a listener because the sound source and the listener have different velocities relative to the medium of sound propagation.

    lf a sound source and a listener move relative to one another and the medium in which the sound is propogated, an apparent change in the frequency of the sound is observed.

    lf they move towards one another, the listener hears a higher frequency (pitch) and if they move away from one another, a lower frequency (pitch), compared to the frequency observed when they are both stationary. This is called the Doppler effect.

    Stationary soundsource, stationary listener

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Moving sound source, stationary listener

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Stationary sound source, moving listener

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Ultrasonic sound or ultrasound has a frequency greater than 20 000 Hz and cannot be heard by the human ear.

    The combination of ultrasound and the Doppler effect is used in various medical equipment, for example to measure the rate of blood flow or to monitor the heartbeat of a foetus in the mother's womb.

    Blood flow rate

    The Doppler effect can be used to indicate constrictions in blood vessels (due to hardened calcium and fatty deposits) and so limit the risk of a heart attack. These constrictions cause blood to flow faster and can be determined by means of a Doppler flow meter.

    The Doppler flow meter is a device that consists of a transmitter and receiver and it is placed directly onto the person's skin. The transmitter transmits an ultrasound with a frequency of 5 MHz. The sound wave hits a moving red blood cell and is reflected back to the receiver.

    • The red blood cells move away from the stationary sound source, which causes the frequency that reaches the blood cell to be lower than the transmitted frequency.
    • The moving red blood cells reflect the sound and serve as a sound source that moves away from the stationary receiver, causing the frequency to decrease further. The receiver receives the reflected sound and measures this frequency in relation to the transmitted frequency. The change in frequency is used to determine a change in the speed of the blood flow.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Heartbeat of a foetus

    A Doppler flow meter can also be used to monitor the heartbeat of an unborn baby. A monitor (on the mother's stomach) sends ultrasound waves by means of a transmitter to the foetus in the womb. The frequency of the sound that is reflected back to the receiver is converted into an audible sound that represents the baby's heartbeat.

    Other uses

    The Doppler effect can also be used in speed traps to determine the speed of a car. A radar device transmits microwaves to moving vehicles. The waves are reflected and received again. The change in frequency can be used to calculate the speed at which the vehicle is moving.

    DOPPLER EFFECT AND LIGHT

    The Doppler effect can also be observed in light waves. ln the spectrum of visible light, red light has the longest wavelength and the lowest frequency, while the blue end of the spectrum is associated with shorter wavelengths and higher frequencies. A change in the frequency of light is observed as a colour change. lf the frequency/colour of light being observed differs from that which is emitted, it is called a shift.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Suppose the light source (star) and observer (on earth) move away from each other:

    The crests of the emitted light waves behind the source will be further apart and waves with a longer wavelength and lower frequency will be observed. To the observer, it seems as if the frequency of the light decreases, shifting to the red side of the spectrum. This is known as red shift.

    Red shifts in the universe:

    • Very hot objects such as the sun and stars emit continuous emission spectra.
    • However, the cold outer gas layers of the star absorb light of specific frequencies and absorption spectra are observed.
    • The gases that the stars consist of determine which light frequencies are being absorbed.
    • Therefore, each star has a specific absorption spectrum.
    • By investigating the absorption spectrum of a star, we can determine if the star is moving towards or away from earth, as well as the speed at which the star is moving.
    • lf a star is moving away from earth, there will be a shift of the spectrum lines to lower frequencies (longer wavelengths), i.e. a red shift takes place.
    • lf a star is moving towards earth, there will be a shift of the spectrum lines to higher frequencies (shorter wavelengths), i.e. a blue shift takes place.

    A cosmological red shift is a phenomenon where predominantly light of a lower frequency (longer wavelength) is observed than the real frequency being emitted by the stars (source), not only because most galaxies in the universe are moving away from earth, but also because the universe itself is expanding.

    CHEMICAL CHANCE

    BOND ENERGY CHANGES

    Bond energy is the energy needed to break the existing bonds/form new bonds in 1 mol of a compound in the gas phase.

    Chemical compounds contain internal energy, mainly due to the way in which their constituent parts (atoms or ions) have bonded with each other.

    During a chemical reaction, existing bonds between the reactant atoms or ions are broken. The free atoms/ions are rearranged and new bonds are formed to produce new products.

    Energy is needed to break existing bonds between the ions or atoms of the reactants. This is called the bond energy. The breaking of bonds is an endothermic process.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    When new bonds are formed, energy is released again. Bond formation is an exothermic process.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The net energy change during the reaction determines whether a reaction is classified as endothermic or exothermic:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Endothermic reactions are reactions that take up energy/transfer heat energy to potential energy.

    Exothermic reactions are reactions that release energy/transfer potiential energy to heat energy.

    ENERGY CHANGE IN CHEMICAL REACTIONS

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    ACTIVATION ENERGY (EA)

    Activation energy is the minimum energy required for a reaction to take place.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    POTENTIAL ENERGY DIAGRAMS

    Below is a potential energy diagram representing the progress of a chemical reaction:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    For the forward reaction: Reactants (R) --> Products (P)

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    An endothermic reaction

    Energy is absorbed from the environment by the reactants and the temperature of the reaction mixture/environment decreases if no heat is added.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    An exothermic reaction

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Energy is released to the reaction mixture/environment and often the temperature rises.

    The energy can also be released in the form of light energy or electrical energy.

    INTRODUGTION

    During a chemical reaction, the rate at which and the extent to which the reactants change into product(s) play a crucial role. During the industrial production of substances, it is important to obtain a high yield at a high reaction rate, as economically as possible.

    WHAT IS MEANT BY THE RATE OF A REAGTION?

    Consider the chemical reaction: Reactants (R) - Products (P) Some reactions take place instantaneously, such as the combustion reaction of petrol. However, other reactions, such as iron that rusts, take much longer.

    The reaction rate describes how quickly or slowly products are formed and the reactants are used up during a reaction.

    The reaction rate indicates the change in the concentration of the reactants or the products per unit time, i.e.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    We can monitor the rate of the reaction by:

    • measuring the decrease in mass of the reactants per time interval
    • measuring the increase in mass or volume of a product (e.9. gas released) per time interval
    • determining the change in concentration of the reactants or products per time interval
    • determining the time it takes for a colour change to occur, etc.

    At the start, the reaction is usually fast (reactants rapidly decrease and products form quickly) but as the reactants are used up, the rate decreases until the reaction stops. The reaction rate can be represented graphically as the change in the the number of mole of either (1) the reactants or (2) the products versus time.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Effective collisions

    According to the collision theory, particles (atoms, molecules or ions)can only react when they collide with each other. Not all collisions result in a reaction, otherwise all reactions would be fast.

    The rate of a reaction is determined by:

    • the number of collisions per unit time, or the frequency of the collisions
    • the energy of the colliding particles, and
    • the orientation of the colliding particles.

      Collisions that result in a reaction are called effective collisions.

    Frequency of collisions

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The energy of particles

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The correct orientation

    To have the correct orientation, the molecules must be oriented in a specific way when they collide with each other, e.g. the H atom side of the HC0 molecule must hit the double bond of ethene to bond.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    FACTORS AFFECTING THE RATE OF A CHEMIGAL REACTION

    There are five factors that affect the rate of a chemical reaction:

    • the nature of the reactants
    • the temperature at which the reaction takes place
    • the concentration of a liquid reactant or the pressure of a gaseous reactant (a compressed gas has a higher concentration)
    • the reaction surface area of a solid reactant > the use of a catalyst

    The effect of each factor can be explained in terms of the collision theory.

    Some chemical compounds are more reactive than others, e.g. the reactivity of the alkali metals increases as you go down the group. Furthermore, potassium and sodium are much more reactive than heavier metals such as zinc and copper. The strength of the bonds between the particles and the activation energy required to break the bonds, influences the rate of the chemical reaction. Therefore simple particles such as atoms or ions in solution will react faster than complex molecules.

    lf the temperature of the reaction mixture increases or decreases, it affects the rate of the chemical reaction.

    According to the collision theory:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    An increase in the concentration of a solution or increase in the pressure of a gas (by decreasing volume) increases the rate of the chemical reaction.

    According to the collision theory:

    With an increase in reactant concentration,

    • there are more particles per unit volume in the container
    • particles therefore collide more frequently
    • more effective collisions occur per unit time > the rate of the reaction thus increases

    The reaction occurs on the surface of the substance. When a solid is divided more finely, e.g. into a powder, the reaction surface area is much greater than in the more compact form.

    According to the collision theory:

    When a solid reactant is more finely divided,

    • there is a greater surface area for collisions to occur
    • more effective collisions will occur per unit time
    • the reaction rate increases

      This is the reason why an antacid tablet that is finely chewed or a painkiller in powder form brings relief much faster.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    A catalyst is a substance that affects the rate of a chemical reaction without undergoing any permanent change or being used up.

    A catalyst can be a solid, liquid or a gas. A distinction is made between:

    • homogeneous catalysis: reactants and catalyst are in the same phase
    • heterogeneous catalysis: reactants and catalyst are in different phases. The catalyst is usually a solid and contact catalysis occurs on the surface of the catalyst.

    Particles of the reactants adhere to the surface of the catalyst and so are oriented correctly. Less activation energy is required to form the activation complex

    Particles of the reactants adhere to the surface of the catalyst and so are oriented correctly. Less activation energy is required to form the activation complex

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    MEASURING REACTION RATE

    The rate of a chemical reaction has already been defined as:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    We cannot determine the rate of very fast reactions because the changes happen too quickly. Consider for example the combustion reactions of fossil fuels.

    Certain reactions have specific qualities that make it possible to measure the rate of the reaction.

    Qualitative methods are based on what we can observe (see, smell, etc.) and include things such as colour changes, the formation of precipitates, etc.

    Quantitative methods use the measurement of mass, volume, etc.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Here are a few examples of different reaction rate graphs:

    lf time is the variable on the x-axis:

    A mass/volume increase (of product) versus time

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    lf time is the dependent variable (y-axis):

    A factor such as temperature or the reaction surface area is changed (independent variable) and the duration of the completed reaction is noted.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    MECHANISM OF A CHEMICAL REACTION AND OF CATALYSIS

    Most chemical reactions take place in more than one step, e.g. the breaking of the existing bonds in a specific order, the forming of transitional products such as an activated complex, and the forming of new bonds.

    A reaction mechanism describes the path of a chemical reaction. lt gives a description of the elementary steps during which the reactants change into products. This includes, for example, collisions between the reactant molecules, the function of the catalyst and the forming of the products.

    The reaction mechanism also indicates the rate of the different steps and shows which step is the slowest and therefore determines the rate of the overall reaction. Scientists use reaction mechanisms to manipulate chemical reactions in the manufacturing process of specific products.

    As mentioned before, not all collisions result in a reaction and all reactions do not take place at the same rate. For a reaction to occur, the colliding reactant particles must have: O the correct orientation, and @ a certain minimum kinetic energy, i.e. the activation energy (E")

    The activation energy is the energy required to break the existing bonds between the atoms/ions and to form a transitional product or activated complex. It is sometimes necessary to supply the activation energy in the form of heat or light. The lower the activation energy, the higher the reaction rate.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    A catalyst is used in many chemical reactions to increase the rate of the reaction. A catalyst provides a different path or mechanism with a lower activation energy along which the reaction can take place.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    CHEMICAL EQUILIBRIUM AND FACTORS AFFECTING CHEMICAL EQUILIBRIUM

    Open and closed systems

    The reactants and products together with the container in which the reaction occurs, are known as the system. Everything outside the system is called the environment.

    An open system continuously interacts with its environment.

    lf the water vapour from the evaporation of water is allowed to escape, it is known as an open system. The gas will not readily be added to the system again, and the reverse condensation reaction will not readily take place.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The container does not have to be closed to be a closed system, e.g. the neutralisation reaction of an acid with an alkali in an open test tube still represents a closed system, because little evaporation takes place and there is no interaction with the environment.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    A reaction is reversible when the products can be converted back to reactants.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Examples of dynamic equilibrium

    Phase equilibrium: liquid => vapour

    Water in a closed system initially evaporates rapidly, but as more water vapour forms, it condenses back into water at an increased rate. At equilibrium the two reactions (evaporation and condensation) take place equally fast and still continue although the water level remains constant.

    Solubility equilibrium: salt + ions in solution

    lf a solution of a salt, e.g. sodium chloride, is made saturated to the point where undissolved salt remains in the beaker, the undissolved salt and the dissolved salt ions are in equilibrium. As the solid substance breaks up into ions (dissociates), the ions again combine into solid form (crystallises).

    Chemical equilibrium

    A reversible chemical reaction (synthesis or decomposition reaction) in a closed system reaches equilibrium when the rate of the forward reaction = the rate of the reverse reaction.

    THE EQUILTBRTUM CONSTANT Kc

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Equilibrium is established at a specific:

    • temperature
    • concentration (liquids)
    • pressure (gases)

    lf any of the conditions are changed, the forward or reverse reaction will be favoured (occur faster) until a new equilibrium is established.

    Equilibrium mixtures of solutions

    The following practical investigation illustrates the effect of the two factors, temperature and concentration, on a solution in equilibrium.

    Gaseous equilibrium mixtures (NO2 / N2O4 equitibrium)

    In mixtures consisting only of gases, the two factors pressure and temperature play a role, e.g.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Le Chatelier's Principle: When the equilibrium in a closed system is disturbed, the system will reinstate a new equilibrium by favouring the reaction that will oppose the disturbance.

    According to Le Chatelier's principle, the reaction that attempts to counteract the effect of the change on the equilibrium system will be favoured.

    Look at the imposed disturbance/change and determine:

    • in which direction the equilibrium shifts (which of the fonrrard or reverse reactions are favoured) by applying Le Chatelier's principle
    • how the concentrations of the reactants and products are affected
    • how the reaction rate is affected
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    General properties

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Well-known acids and bases

    Acids

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Bases

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Definition of acids and base

    Arrhenius's definition

    In 1884, a swedish chemist, svante Arrhenius, formulated definitions for acids and bases as follows:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    This definition, however, limits acids and bases to aqueous solutions only. (Bases are then also limited to hydroxides only.)

    The Bronsted-Lowry theory

    In the 1920s, two chemists, Bronsted and Lowry, respectively from Denmark and England, independently formulated new definitions for acids and bases, known as the Bronsted-Lowry theory which reads as follows:

    An acid is a proton (H*)donor (in the presence of a base).

    A base is a proton (H*) acceptor (in the presence of an acid).

    Therefore, a reaction of an acid with a base involves the transfer of a proton from the acid to the base. This is also called a proton transfer or a protolysis reaction. Acid-base reactions are no longer only limited to reactions in an aqueous medium.

    Proton transfer reaction

    The following general equation shows how a proton is transferred from an acid to a base during an acid-base reaction:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The concentration of acids and bases refers to the number of moles of substance dissolved in '1 dm3 water.

    A concentrated acid or base contains many molecules of acid/base in proportion to the volume of water in the solution.

    A diluted acid or base contains few molecules of acid/base in proportion to the volume of water in the solution.

    Concentrated hydrochloric acid contains about 33 g hydrochloric acid per '100 g water. lt can be diluted by adding a small amount of acid to an amount of water.

    The strength of acids or bases refers to the extent of ionisation. Both strong and weak acids or bases can be concentrated or diluted.

    The conjugate base of an acid

    The conjugate base of an acid is the ion or molecule that remains when the acid has donated a proton

    When an acid has donated a proton, the remaining ion is called a conjugate base because it can accept a proton in the reverse reaction again.

    The conjugate acid of a base

    The conjugate acid of a base is the ion or molecule that forms when the base has accepted a proton

    When a base has accepted a proton, the formed product is called a conjugate acid, as it can donate a proton in the reverse reaction again.

    Net reaction

    Therefore, acid-base reactions are a combination of these half-reactions during which O the acid donates a proton and O the base accepts it at the same time ln the net reaction, the conjugate acid-base pairs can be paired off, i.e.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Isolation of salts from solutions

    • A stoichiometric calculation can determine the number of moles of acid and base, respectively, that must be combined so that they react completely with each other, without leaving excess unreacted reactants.
    • The salts that form during acid-base reactions mostly remain in solution and are therefore invisible.
    • Once the reaction is completed, the reaction mixture with the salt and water could be left in an open container until allthe water has evaporated and the salt is isolated.
    • During the evaporation process, the positive and negative ions combine and ionic salt crystals remain as a residue in the container.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The strength of acids and bases

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    lf the concentration of an acid or alkali is unknown, it can be determined by way of a titration reaction with an alkali or acid of known concentration. The volumes of acid or alkali necessary to neutralise each other (at the equivalence point) are used in the calculation. This method is known as the volumetric analysis of an unknown concentration of an acid or base.

    Preparation of a standard solution

    A standard solution is a solution of :r: which the exact concentration is known.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Choose an indicator

    Acid-base titrations are based on a neutralisation reaction in which a salt and water are formed. An indicator is added to the solution to determine the endpoint. The pH of the solution at the endpoint depends on the strength of the acid or alkali being used. The correct indicator must be chosen so that the pH at the endpoint falls within the transition range of the indicator

    Equivalence point: the point during a titration where the acid/base has reacted completely with the base/acid.

    Endpoint: the point during a titration where the indicator changes colour.

    The following guidelines can be used:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The chlor-alkali industry

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Electrochemistry involves chemical reactions where chemical energy is converted to electrical energy or electrical energy to chemical energy.

    Electrochemical processes involve oxidation-red uction reactions or redox reactions where electrons are transferred between substances.

    ELECTROCHEMIGAL CELL

    An electrochemical cell consists of a combination of two electrodes (an anode and cathode), which are placed in an electrolyte (salt solution, or molten salt, containing moving ions) and connected to an external circuit. A chemical reaction takes place resulting in electrons moving from the anode, through the external circuit, to the cathode. The movement of the ions through the electrolyte completes the circuit.

    There are two types of electrochemical cells:

    Galvanic cell: A cell in which chemical energy is converted to electrical energy. A galvanic cell has self-sustaining electrode reactions.

    A spontaneous chemical reaction takes place during which chemical energy is converted to electrical energy and an electrical current is generated. A battery is an example of a galvanic cell in which electrical potential energy becomes available through a chemical reaction taking place in the battery.

    Electrolytic cell: A cell in which electrical energy is converted to chemical energy.

    An electric current drives a non-spontaneous chemical reaction and electrical energy is converted to chemical energy. By supplying electrical energy, chemical decomposition reactions can take place, which have important applications such as electroplating, purification of metals, etc.

    ln both cells, the chemical reaction can be divided into two half-reactions in which electron transfer takes place; an oxidation half-reaction and a reduction half-reaction.

    Oxidation and reduction

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    OXIDATION NUMBERS

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Rules for the allocation of oxidation numbers

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Allocation of oxidation numbers to atoms in a compound

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Direct electron transfer

    If a spontaneous redox reaction (comprising an oxidation and reduction halfreaction) takes place in the same beaker, electrons are transferred directly from one reactant to another:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Indirect electron transfer

    The two half-reactions can be separated by placing them in separate beakers that are connected by a salt bridge. Electrons move in an external circuit from the anode to the cathode.

    The galvanic cell

    Consider the Zn/Cu galvanic cell

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The structure of the galvanic cell

    • ln a galvanic cell, the two half-reactions are separated into two separate half-cells.
    • Each half-cell consists of an electrode (anode (A) or cathode (C)) in contact with an electrolyte (E) which contains ions corresponding to the electrode.
    • The electrodes are connected to each other in an external circuit consisting of conducting wires (C) and a voltmeter (V).
    • The circuit is completed by a salt bridge (S).
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Electrolyte: A solution/liquid/dissolved substance that conducts electricity through the movement of ions.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Functions of the salt bridge

    The salt bridge :

    • separates the electrolytes so that they do not mix.
    • completes the circuit.
    • supplies a path through which ions can move to restore neutrality.

    Cell notation

    A shortened cell notation can be used to represent the galvanic cell:

    The cell terminals (electrodes) are written on the extreme left and right sides of the cell notation. By convention, the anode is always on the left and the cathode on the right.

    For active electrodes:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Cell potential

    • When a galvanic cellwith two half-cells is set up, oxidation occurs in the one half-cell and reduction occurs in the other. The tendencyi'potential' of an electrode/electrolyte to be reduced or oxidised determines which reaction takes place in a particular half-cell.
    • In the half-cell where oxidation occurs, the electrode has a negative charge and the electrolyte has a positive charge.
    • A potential difference forms between the negative electrode and the positive solution. This is called the electrode potential (half-cell potential).
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Standard conditions

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Determining the standard electrode potentials (E0half-cell)

    To measure a single half-cell potential, we must produce a half-cell with an electrode potential of 0,00 V. This is called the reference electrode. By connecting the reference electrode to another half-cell (at standard conditions) and taking the voltmeter reading we then obtain the standard electrode potential of that specific half-cell compared to that of the reference electrode. The potential difference reading gets the same sign as the charge on the electrode connected to the reference electrode.

    The standard hydrogen electrode

    The hydrogen electrode (H2) has been chosen as the reference electrode (the electrode (half-cell)to which the other half-cells are compared).

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Table of standard reduction potentials

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Using standard electrode potentials in practice

    The list of electrode potentials is useful to:

    • write down and balance chemical equations involving redox reactions
    • calculate the emf of electrochemical cells
    • predict if a given redox reaction will take place spontaneously

    The cell potential of a galvanrc cell depends on the concentrations of the electrolytes as well as conditions of temperature and pressure. The table is set up for standard conditions. (See pg. xiii.) The emf or voltage of a galvanic cell at standard conditions can be calculated as follows:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    EQUATIONS FOR OXIDATION-REDUCTION REACTIONS

    Use the table of standard reduction potentials and determine the oxidation halfreaction, reduction half-reaction and net redox reaction.

    1) ldentify the reactants involved in the reaction, i.e. identify the two redox pairs. (Check if any of the elements show no change in oxidation number. Usually, these are spectator ions.)

    2) Find the relevant half-reactions in the list of reduction potentials (4A or 4B). (There may be H. ions present, indicating an acid medium or the production of HzO molecules.)  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    RELATIONSHIP OF CURRENT STRENGTH AND POTENTIAL DIFFERENCE TO REACTION RATE AND EQUILIBRIUM

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The cell potential or emf of a galvanic cell or battery is the energy per unit charge that makes the electrical current flow. The emf depends on each halfcell reaction and the net cell reaction.

    Current strength is defined as the rate of flow of charge and is therefore determined by the rate at which electrons leave the anode or arrive at the cathode

    The strength of the current supplied by the cell thus depends on the rate of the net cell reaction.

    Factors that increase the rate of the cell reaction:

    • The half-reactions take place on the surface of the electrodes. lf the size of the electrodes is increased, the contact area with the reactants is enlarged and this lncreases the reaction rate.
    • An increase in the concentration of the electrolytes will also increase the reaction rate and thus the current strength.
    • A lower internal resistance will also result in a stronger current. (An increase in electrode size, increased electrolyte concentration and a broader, shorter salt bridge which decreases fhe distance between the electrodes, contributing to the decrease in internal resistance.)
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Electrolysis is the chemical process in which electrical energy is converted to chemical energy OR the use of electrical energy to produce chemical change.

    The apparatus used for electrolysis is an electrolytic cell, consisting of the following parts:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Functioning of the electrolytic cell

    • The cell contains two unreactive electrodes (anode and cathode), e.g. graphite/carbon or platinum (which will not react with the electrolyte or the products of electrolysis).
    • The electrodes carry electrical current in and out of the electrolyte.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Electroplating

    Electroplating is the process by which a metal object is coated with another metal to improve its appearance, to protect it or to give it other useful qualities.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Purtfying/Refining of metal

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The chlor-alkali industry

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The recovery of aluminium

    • The reddish brown mud pumped into the slime dams and the sea is a mixture of undissolved bauxite containing iron(III) oxide, silicon and titanium. lt defaces the environment and contributes to environmental pollution. lt is an alkaline fluid that filters into the ground and also pollutes water sources.
    • A compound HF forms as a result of the presence of cryolite. lt is a very corrosive gas that poses an environmental danger.
    • The electricity consumption for most of the electrolysis processes, and specifically for the recovery of aluminium, is extremely high. Therefore, it uses valuable, non-renewable resources, e.g. coal. lt also contributes to globalwarming.
    • Large amounts of water are also used.
    CHEMICAL CHANCE

    ELEGTROSTATICS

    Electrostatics is the study of interacting static charges or charges at rest.

    We know:

    • An object acquires a positive or negative charge because of the loss of electrons from the object (+ charge) or the gain of electrons by the object (- charge).
    • lnsulators (e.9. plastic, rubber, wool) can be charged by friction and can conserve the charge (e.9. a ruler that is rubbed acquires a static charge).
    • Conductors (metals) can be charged by contact or induction, but the charge may pass through the conductor and flow away.
    • The smallest charge an object can have is when it gains or loses one electron. This is known as the elementary charge, i.e qe = 1,6 x 10-19 C.
    • Charge is quantised and all charges are integer multiples. of qe: Q = nqe

    Law of conservation of charge

    Charge cannot be created or destroyed, but can only be transferred from one object to another' Or The total amount of charge in a closed system remains constant.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    COULOMB'S LAW

    Force between charges

    The scientist Charles de Coulomb investigated the force that charges/charged objects exerted on each other. He found that:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    One dimension

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Example 2

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    An electric field is an invisible force field around a charge and can only be observed by the force of attraction or repulsion that itlxerts on another charged object.

    Electric field around charges

    Consider a test charge (q) praced at any point in space near another charge (Q):

    • The force the test charge (q)experiences, shows the magnitude and direction of the electric field around the charge (e) at that point.
    • lmaginary field lines are used to represent an electric field, e.g.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    An electric field (E-field) is the region of space in which an electric charge will experience a force.

    The direction of the electric field at a point is the direction that a , positive test charge (+q) would move if placed at that point (from + to -).

    Electric field lines are imaginary lines used to represent the three dimensional force field existing around an electric charge.

    Examples of electric field lines around:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Force experienced bycharge in an electric field

    The magnitude of the electrostatic force exerted by an electric field on another charge in the field can be calculated as follows:

    F=qE

    Electric field strength at a distance r from point charge Q

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Charges in a straight line (1-D)

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    A simple electric circuit contains a battery or other source of electrical energy (e.9. a dynamo) that is connected with electrical conducting wire to resistors and other electrical components.

    charges in the conductor continuously receive energy from the battery, move around the circuit and transfer their energy to activate the components such as light bulbs.

    Although the moving charges in most metal conductors are electrons, we work with conventional current, i.e. the flow of positive charge from the positive to the negative terminal of the battery.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The potential difference between two points in a circuit

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
    • Suppose a battery with an emf of 10 V is connected in a circuit. ln the battery, chemical energy is converted into electrical energy and it is provided to each 1 C of charge that leaves the battery.
    • Therefore, '10 J of electrical potential energy per coulomb of charge is available to transfer to the electrical components in the external circuit (assume that the battery has no internal resistance).
    • Charge moves from a point of high potential (point A) to a point of low potential (point F).
    • The potential difference between point A and point F of the external circuit is 10 v.
    • As the charge moves through a component, electrical energy is transferred to the component and is converted into light or heat energy, e.g. each '1 C of charge that passes through R1, transfers 6 J of energy to it. The decrease in energy causes a potential difference of 6 V between B and C.
    • Similarly, 4 J of energy per 1 C of charge is transferred to Rz, and the potential difference between D and E is 4 V.
    • There is no potential difference across parts of the circuit that have no resistance, e.g. across the ammeter or closed switch or any connecting wires. No electrical potential energy is transferred to the part EF of the circuit. The potential difference between E and F is zero.
    • The total potential difference across the external circuit is divided between the series components in the circuit.

    OHM'S LAW

    Ohm's law: the potential difference across a resistor is directly proportional to the current strength through the resistor, provided the temperature remains constant.

    Relationship between V, I and R

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Ohmic and non-ohmic conductors

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Resistors in series

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Resistors in parallel

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Circuit calculations

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Emf and internal resistance of a battery

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Switches in circuits

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Work done (W) or energy transferred (E) in a circuit

    When charge moves through a closed circuit, energy is transferred to the components, e.g. a light bulb, to perform a certain function, e.g. supplying light. The energy transferred to or work done by the component can be calculated as follows:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Power

    Electric power is the rate at which electrical energy is transferred o1 work is done.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Electrical energy transferred/used

    The electrical energy used by an electric appliance such as a kettle, heater or light bulb depends on the power of the appliance as well as the length of time rt is switched on.

    Energy consumption = power x time interval

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The amount of electricity used by consumers is expressed in terms of kilowatt-hour (kWh ).

    1 kilowatt-hour refers to the use of 1 kilowatt of electricityfor t hour, therefore 1 kwh = I kWx t h.

    lf an appliance marked 1 500 W is switched on for 30 minutes, then the electricity consumption is as follows:

    Consumption (number of kWh)
    = P (kilowatt) x time (hour)
    = 1,5 x 0,5
    = 0,75 kWh

    Cost of electricity consumption

    The cost of electricity consumption per month is calculated according to a tariff (usually in R/c) per kilowatt-hour used:

    Total cost = number of kilowatt-hour x tariff/kWh

    Suppose a household uses 100 kWh per month and the electricity tariff is 75 cents per kWh, then:

    Total cost
    = number of kWh x tariff
    = 100x75
    = 7 500 cents
    = R75

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Electrodynamics is the branch of physics that deals with the interaction between electricity, magnetism and movement.

    ELECTRICAL MACHINES (GENERATORS AND MOTORS)

    Electrical generators and motors are two electric devices that are used for the generation of electricity and the powering and operation of machines, respectively. We can hardly imagine modern life without them. In a generator, mechanical energy is converted into electricalenergy. ln a motor, electrical energy is converted into mechanicalenergy.

    Electromagnetic induction

    Electromagnetic induction: an emf as well as an electric current are induced in a conductor tnat is placed in a changing magnetic field.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Faraday's law of electromagnetic induction: A changing magnetic field induces an emf in a conductor. The magnitude of the emf induced is directly proportional to the rate of change of magnetic flux.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The alternating current (AC) generator / alternator

    A simple generator that can generate alternating current, known as an alternating-current (AC) generator or alternator, consists of the following parts:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.
     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The power of an AC source fluctuates between zero and a maximum for each half AC cycle. Power (P) = VI

    The following sketch shows the graphs of voltage and current strength versus time. The product of V and I gives the corresponding power values for the power/time graph indicated on the same set of axes. The average value of the power is half of the maximum value.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Motor effect

    The functioning of electric motors is based on the motor effect, i.e. a currentcarrying conductor in a magnetic field experiences a force.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The direct-current electric motor (DC motor)

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    The split-ring commutator

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Factors that improve the operation of a motor

    The force that a current-carrying conductor experiences in a magnetic field will increase with the application of the following factors:

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Motors in everyday life

    • ln practice, the coil of a motor consists of a soft iron core with several turns/coils of wire, placed at different angles. This results in a constant force being exerted on the coil, enabling it to rotate at high speed
    • The motors in some appliances, such as an electric drill, contain electromagnets instead of permanent magnets. As the AC around the electromagnet changes direction, the direction of the magnetic field changes, and therefore the motor will turn rn the same direction. All motors in household appliances should be able to work with AC, because our houses are supplied with AC current
    • The operation and hence design of a specific type of motor depends on the task it has to perform, i.e. whether it should rotate fast (drill), rotate back and forth (washing machine), progress step by step, etc.

    The AC generator looks much like the DC motor, but note the following differences:

    • The DC motor uses the interaction of an electric current with a magnetic field to obtain movement/torque, while the AC generator uses the movement/torque of the coil in a magnetic field to generate an electric current (i.e. reverse process).
    • Electric motors convert electrical energy to mechanical energy; but an electric generator converts mechanical energy to electrical energy.
    • The DC motor contains a split-ring commutator and carbon brushes; but the AC generator contains slip rings and carbon brushes.
    • The AC generator has a handle through which Emechnical (Ek) is supplied and the DC motor contains a battery to supply Eelectrical.

    Uses of AC and DC generators

    AG generators

    • An AC generator, known as an alternator, is used in modern cars to charge the battery and to provide the electrical system with power while the engine runs.
    • Important components such as the capacitors and inductors used in electronics require alternating current in order to perform certain functions.
    • Transformers, which are used to decrease/increase potential difference, can only function with AC. Transformers play a significant role in the delivery of electrical energy from power stations to the consumer

    DG generators

    • Electrochemical reactions, e.g. the charging of batteries and electroplating, require direct current. (The charge on the electrodes must remain the same.)
    • ln electronic devices, such as radio and television receivers.
    • Power supply to electric trains/buses.
    CHEMICAL SYSTEMS

    Plants absorb the chemical elements they need in order to produce their own food and grow. These elements are absorbed from the atmosphere through the leaves (during the process of photosynthesis) and from the soil through the roots. These chemical elements are called plant nutrients. As more and more nutrients are taken from the soil, the soil becomes depleted or leached. lt is important to return nutrients to the soil, otherwise indigenous plants will not grow and soil erosion will take place. This also means that fewer crops can be cultivated. With the growing world population there is an ever-increasing demand for food. This means that more crops must be cultivated more often on the same fields. This is not possible without using fertilisers.

    PLANT NUTRIENTS

    Macronutrients

    Macronutrients are the main elements needed by plants in greater quantities for optimal growth and can be classified as follows:

    Non-mineral nutrients

    Plants produce their own organic food from the three non-mineral nutrients, C, H and O, by means of photosynthesis.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Mineral nutrients

    Mineral nutrients occur in compounds that dissolve in groundwater and are absorbed by the roots of the plant.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    These nutrients are needed in smaller quantities by plants for their growth. Micronutrients include various mineral nutrients that, when dissolved in groundwater, can be absorbed by the plants through their roots, e.g. Fe, C0, Cu, Mn, Zn, B, Mo.

    HUMAN NUTRIENTS

    Just like plants, humans need certain nutrients for healthy and normal growth. Four of the most important elements needed by the human body are:

    • carbon (C)
    • oxygen (O)
    • hydrogen (H)
    • nitrogen (N)

    Oxygen is absorbed from the atmosphere by breathing.

    C, H and N are taken in by drinking water and eating food. The plant and animal materials we eat are the main sources of these four important elements.

    THE ELEMENTS N, P, K

    Usable forms of N, P and K for plants and animals

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Phosphorus (P): root growth

    Phosphorus is dangerous in its elementalform as it explodes in air. lt occurs in compounds in the soil that are primarily insoluble. This means that they cannot be absorbed by plants.

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Types of fertilisers

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Industrial preparation of fertilisers

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.  You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Eutrophication occurs when an excess of soluble nutrients enters water sources (rivers, dams, lakes)" Plant growth is therefore stimulated and the resultant decrease in oxygen levels leads to the death of fish and other organisms in the water

    Causes and consequences

    • When fields are overfertilised with organic manure, compost or artificial fertilisers, soluble nutrients, such as nitrates and phosphates, are washed out of the soil and swept away into streams, dams and rivers.
    • Nitrogen oxide gases (byproducts of factories and exhaust gases) can also dissolve in rainwater and contribute to increased nitrogen levels in groundwater.
    • The excess of these elements in dams or rivers causes the water plants, especially algae, to grow much faster than normal.
    • This drastic increase in algae blocks sunlight from other photosynthesising organisms. Water plants die as a result.
    • The decomposition of dead organic matter leads to a huge increase in bacteria.
    • Oxygen is necessary for decomposition so oxygen supplies in the water are further depleted.
    • As a result, a great number of fish and other aquatic organisms die due to a shortage in oxygen

    lmpact on humans and the environment

     You don't have internet connection to view more content : 1) Slide your screen to left and Download the Offfline package for offline viewing.

    Prevention of and solutions to the problem

    Without fertilisers we cannot produce enough food for the world's populations and millions of people will die of hunger.

    The use of fertilisers does have negative consequences, as discussed above. They must therefore be used with discretion.

    • Farmers should use the correct quantities of fertilisers at the right times during the growth period. This will ensure they can be used up by plants and not leached into the groundwater.
    • other causes, such as the dumping of sewage and chemical wastes into water sources, must be addressed.
    • Pollution by factories etc. must be limited
    back