CURRICULUM GRADE 10 TO 12

FINAL REVISION SUPPORT DOCUMENT

GRADE 12

2016

Physical Sciences

Mechanics

Unit 1: NEWTON’S LAWS

Multiple Choice Questions (MCQ)

Question 1

1.1 A body is moving northwards. Which one of the following quantities MUST also be northwards

A Resultant force

B velocity

C kinetic energy

D Acceleration (2)

1.2 A body moving at CONSTANT VELOCITY on a horizontal plane, has a number of unequal forces acting on it. Which of the following statements is true?

A At least two of the forces must be acting in the same direction.

B The resultant of the forces is zero.

C Friction between the body and the plane causes a resultant force.

D The vector sum of the forces causes a resultant force which acts in the direction of motion. (2)

1.3. Trolley P, mass m, rests on a frictionless, horizontal surface. A force F is

applied, causing the trolley to accelerate with magnitude a, as shown. Trolley P is replaced with another trolley Q, mass 3m.

A 13a B 1

2a

C 2a D 3a

2

F

m

F 3m

P

Q

a = a

a = ?

1.4 An object of mass m rests on a rough, inclined plane.

Which ONE of the following equals the normal force?

A Static friction B Weight parallel component

C Weight perpendicular component D Weight (2)

1.5 Ziyanda places 4 two-rand coins, one above the other, on a horizontal table. Friction is negligible. She shoots another two-rand coin (X) which strikes the lowest coin horizontally. Coin X displaces and replaces the lowest coin, while all the other coins remain at the same place on the table.

Two-rand coins

Displaced coin

Which ONE of the following laws explains why the top three coins are not displaced?

A Newton's First Law of Motion B Newton's Third Law of Motion

C Law of Conservation of Moment D Law of Conservation of Energy (2)

Question 2 (DBE 2002 SG)

In a show, passengers in a cage hanging from a cable are accelerated vertically upwards by a winch ( motorized pulley). The mass of the cage and the passengers is 750 kg.

2.1 Make a labelled sketch showing all the forces acting on the cage plus passengers while it is accelerated upwards. (4)

2.2 The cable exerts an upward force of 7 950 N on the cage. Calculate the magnitude of the resultant acceleration. (5)

2.3 Name and state the physical law you used to solve Question 2.2. (4)

The cage stops at a height of 50m. Each passenger fastens one end of an ELASTIC rope of length 20m to their waist; the other end being tied to the cage. When a passenger jumps from the cage, he/she falls freely until pulled back by the elastic rope.

2.4 Explain, giving reasons, the direction of the resultant acceleration after the jumper has fallen further than 20m. (4)

3

R

Fg

Fg is the force exerted by the earth on the object.

X

[17]

QUESTION 3 [SG 2003]

3.1 Newton’s Second Law of Motion, as applied to a uniformly accelerated mass, is given by F = ma.

3.1.1 What does the symbol F represent? (2)

3.1.2 What is the direction of a in comparison with that of F? (1)

3.1.3 Use the above equation to define one newton. (2)

3.2 A resultant force acts on a body of mass m, moving on a horizontal, frictionless surface. What will be the resulting motion of the object if the resultant force becomes zero? (2)

3.3 An advertisement claims that a motorcycle can reach a velocity of 25 m.s-1, from rest in first gear, in 4 s. The mass of the motorcycle and rider together is 260 kg. Ignore air resistance.

3.3.1. Calculate the magnitude of the acceleration of the motorcycle (4)

3.3.2 Calculate the magnitude of the resultant force. (3)

3.3.3 Calculate the kinetic energy of the motorcycle at 4 s. (3)

[17]

Question 4

A breakdown truck, T, pulls a car, C, using a light, inelastic rope, as shown in the diagram below. The two vehicles move on a straight, horizontal road to the right.

4.1 State, in words, Newton's Second Law of Motion. (3)

As they start from rest, the rope exerts a horizontal force of 1 160 N on the car. The mass of the car is 1 400 kg. The force of friction on car C, as it starts to move, is 600 N.

4.2 Calculate:

4.2.1 The magnitude and direction of the resultant force which the car experiences at the start (3)

4.2.2 The magnitude of the acceleration of the car at the start (4)

After a while the breakdown truck and the car travel at constant velocity. At that stage, the force exerted by the rope on the car, is 450 N.

4.3 What is the magnitude and direction of the force of friction on the car now? (2)

4

1 400 kg T C rope 1 160 N

Towing with a rope can be dangerous. This is especially true in the event of the breakdown truck applying its brakes suddenly, while the car continues moving forward.

4.4 Name the relevant physical property that is applicable to the car in this situation (2)

[14]

QUESTION 5 [HG 2004]

A horse pulls a cart, C, mass 240 kg, attached to a log of wood, W, mass 80 kg, on a horizontal road. W is tied to the back of C by means of an inelastic rope, which is inclined at 30° to the horizontal. The horse applies a force of 170 N on cart C and the system accelerates at 0,3 m.s-2 to the left. The force of friction on cart C is 40 N. The rope has negligible mass.

5.1 Draw a force diagram for cart C, indicating and labelling all the forces acting on it (4)

5.2 Calculate:

5.2.1 The magnitude of the force which the rope exerts on C (8)

5.2.2 The force of friction on W (6)

[18]

Unit 2: Momentum and Impulse

Multiple Choice Questions

Question 1

1.1 A stone is thrown vertically upwards into the air. Which combination in the table below shows the correct change in the momentum and the potential energy of the stone?(Ignore the effects of air friction)

Momentum Potential energy

A Increases Decreases

B Decreases Increases

C Increases Increases

D Decreases Stays constant (2)

1.2 The same force is applied to trolley A and trolley B as shown in the sketch below.

A B

5

a = 0,3 m.s– 2

rope

30°

170 N Horse

Wood W 80 kg

Cart C 240 kg

The mass of A is TWICE the mass of B. If the rate of change of momentum of A is x, then the

rate of change of momentum of B will be:

A ½ x B x

C 2x D 4x (2)

1.2 A boy, mass 2m, and a girl, mass m, standing on skateboards are facing each other. They push off against one another. The boy exerts a force on the girl and the boy experiences a change in momentum to the left.

Ignore the effects of friction. Which ONE of the following best describes the magnitudes of the force exerted by the girl and her change in momentum?

Force exerted by girl Change in momentum of girl

A Less than the force exerted by the boy

less than the change in momentum of the boy

B less than the force exerted by the boy equal to the change in momentum the boy

C equal to the force exerted by the boy equal to the change in momentum of the boy

D equal to the force exerted by the boy less than the change in momentum of the boy (2)

1.3 The front of a modern car is designed to crumble in case of a head-on collision. The chance of serious injuries to the passenger is reduced because the …

A net force acting on the passenger is reduced, since the contact time for the car to stop decreases

B net force acting on the passenger is reduced, since the rate of change in momentum decreases.

C net force acting on the passenger is reduced, since the change in momentum is reduced.

D Net force acting on the passenger is reduced, since the change in momentum is increased.

1.4 Car B has stopped at an intersection where the lights have gone red. Car A which has a greater mass than car B does not stop and runs into the back of car B as shown in the sketch below.

6

Red light

Which ONE of the following statements is true at the time of collision, about the magnitude of the forces they exert on each other?

A B exerts a force on A, but A does not exert a force on B.

B The magnitude of the force exerted by B on A is equal to the magnitude of the force by A on B.

C The magnitude of the force exerted by B on A is greater than the magnitude of the force A exerts on B.

D The magnitude of the force exerted by A on B is greater than the magnitude of the force exerted by B on A. (2)

A ball of mass m, moving horizontally to the right, strikes the wall with a velocity of 4 m·s-1.The ball rebounds in the opposite direction with a velocity of 2 m.s'. Which ONE of the options below correctly represents the momentum vectors of the initial momentum (Pi),the final momentum (Pt)and the change in momentum (~p) of the ball in kg'm's-1?

1.5 An ELASTIC collision occurs between two bodies in an isolated system. Which ONE of the following combinations of momentum and kinetic energy of the system is CORRECT?

MOMENTUM KINETIC ENERGY

A Conserved conserved

B Conserved not conserved

C not conserved conserved

D not conserved Not conserved. (2)

QUESTION 2 (NW/September 2015)

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Two carts, m1 and m2 of masses 400 g and 1 200 g are free to move on a frictionless horizontal s u r f a c e . The carts are joined by a compressed s p r i n g and tied together by a string. The carts are initially at rest as shown in the figure below.

When the string between them is cut, the spring between them is released. The carts then move away from each other.

2.1 While the spring is expanding:

2.1.1

Compare the magnitudes o f the forces acting on carts m, and m2 at any instant.

Write Fm1 > Fm2, Fm1 < Fm 2 or Fm1 = Fm2

(1)

2.1.2

Name the law or principle applied to obtain the above answer (1)

2.2 After the spring has expanded

2.2.1

How do the magnitudes o f the velocity of the carts m1 and m2 compare?

Write Vm1 > Vm2, Vm1 < Vm 2 or Vm1 = Vm2

(1)

2.2.2

Name the law or principle applied to obtain the above answer (1)

2.3 If 0,225 J of energy is imparted to the carts when the spring between them is released, show that the final speed of m2 is 0,31 rn.s-1. Assume that there was no loss of energy.

(6)

[10]

QUESTION 3 (WINELAND/SEPT 2015)

A boy on a skateboard moves to the right at constant velocity. The joint mass of the boy and skateboard is 50 kg. He catches a ball with of mass 0,4 kg that is travelling

horizontally to the left at a velocity of 6 m·s-1. After the boy catches the ball, they both

move to the right at 1,49 m·s-1.

3.1 Define the term impulse (2)

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3.2 Calculate the magnitude of the average force that the boy exerts on the ball when he catches it, if he and the ball exert a force for a period of 0, 1 s on each other

(3)

3.3 Write down the Principle of Conservation of Momentum. (2)

3.4 Calculate the magnitude of the velocity v of the boy before he catches the ball (3)

3.5 Prove with the necessary calculation that this is an inelastic collision (5)

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9

N

W E

S

QUESTION 4 (MP/SEPT 2015)

A toy canon, mass 1,6 kg, is at rest on a rough horizontal surface as shown in the diagram. A steel marble, mass 0,8 kg, is fired horizontally to the east from the canon. Immediately

after firing the marble, the canon moves at 0,26 m·s-1 to the west.

4.1 Calculate the speed of the steel marble immediately after firing the marble (4)

4.2 The steel marble experiences a force F during the firing. Explain in terms of F how the force experienced by the CANON compares with that experienced by the steel marble. (3)

4.3 The canon reaches point A with a speed of 0,2 m·s-1 and then moves down a rough 0,5 m long slope AB. (1)

Explain why this is NOT a closed system

4.4 Calculate the kinetic frictional force experienced by the canon as it moves from A to B if the coefficient of kinetic friction (µk) is 0,12. (3)

4.5 Using ENERGY PRINCIPLES only, calculate the velocity of the canon at point B (5)

QUESTION 5 (LIMP/ September 2015)

A 0,5 kg soccer ball, moving horizontally at 6 m.s–1, collides with a soccer player’s

head and is headed directly back at 9 m.s–1. The ball is in contact with the player’s head for 0,02 s. Ignore the effects of friction.

5.1 What is the relationship between impulse and change in momentum? (1)

5.2 Is the total momentum conserved during this collision? Provide a reason for your answer. (2)

5.3 Calculate the magnitude of the average force exerted by the soccer player’s head on the ball. (4)

5.4 A second ball is pumped to its maximum volume so that it cannot be compressed. Assume that the two balls have the same mass. If the second ball strikes the soccer player’s head

with a velocity of 6 m.s–1,will the force exerted by the soccer player's head on the ball be

(3)

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greater than, less than or equal to the force calculated in question 5.3. Give a reason for your answer.

[10]

QUESTION 6 (NC/SEPT 2015)

A block of mass 6 kg slides to the right with a constant velocity of 8m·s-1 on a horizontal, frictionless surface. It collides with a stationary block of mass 5 kg. The blocks move together to the right as a single system along the same surface. Refer to the diagram below

6.1 State the law of conservation of linear momentum in words (2)

6.2 Calculate the velocity of the system of two blocks immediately after the collision (4)

The block system continues moving with the same common velocity to point A, then

continues over the rough section AB, a distance of 2 m passing point B at 1,5 m·s-1. The system continues up the rough ramp, finally coming to a stop after moving a distance d as shown in the diagram

6.3 Use energy considerations ONLY to calculate the coefficient of sliding friction between the block system and the surface over the 2 m stretch (5)

6.4 The system of two blocks slides up the rough ramp with the same coefficient of friction until they come to rest after covering a distance “d”.

6.4.1 Use NEWTON'S SECOND LAW of motion to calculate the distance d. (7)

6.4.2 How would the answer to QUESTION 6.4.1 change if the angle of

inclination is less than 30o? Write only INCREASES, DECREASES or REMAINS THE SAME .

Give a reason for the answer (2)

[20]

QUESTION 7 ( EC/ SEPT 2015)

A boy on a skateboard moves at 5 m.s-1 to the right towards point A at the bottom of a slope which is 1,6 m high. He is carrying a 4 kg parcel. The total mass of the boy, his skateboard and the parcel is 70 kg. He needs to increase his speed, in order to reach point B at the top of the slope. He decides that if he throws the parcel horizontally, it will increase his forward velocity. IGNORE ALL FRICTION.

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7.1 In which direction must the boy throw the parcel in order to increase his forward velocity? (TO THE LEFT or TO THE RIGHT) (1)

7.2 Give the name of Newton’s law of Motion that you used to obtain your answer in QUESTION 7.1. (1)

7.3 State the Principle of conservation of mechanical energy (2)

7.4 Calculate the velocity of the boy immediately after the parcel leaves his hand in order for him to reach the top of the slope at point B (4)

7.5 Calculate the minimum velocity with which he must throw the parcel in order for him to reach the top of the slope at point B (4)

7.6 How will the answer in QUESTION 7.4 be affected, if the boy throws the same parcel with higher velocity in the same direction as indicated in QUESTION 7.1?Write down INCREASES, DECREASES or REMAIN THE SAME. Explain your answer. (3)

QUESTION 8 (WC METRO/SEPT 2015)

A wooden block of mass 2 kg, moving at a velocity of 5 m.s-1, collides with a crate of mass 9 kg resting on a flat horizontal surface as shown in the diagram below. After the collision,

the crate moves to the right at 1 m.s-1. Ignore the effects of friction.

8.1 Write down the principle of conservation of linear momentum in words. (2)

8.2 Calculate the magnitude of the velocity of the wooden block immediately after the collision. (4)

8.3 If the collision lasts 0,6 seconds, calculate the force the wooden block exerts on the crate during the collision (4)

[10]

QUESTION 9 BALLISTIC EXPERIMENTS

NB: This experiment was carried out in an open field alongside a high brick wall for safety reasons

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A Physics student decides to investigate how the impact speed of a pellet fired from his air rifle is affected by the distance from the target. He decides to fire the pellet gun at an apple which is suspended from a light string. The pellet gets stuck in the apple when it is fired.

The apple and the pellet swing away to the right, as shown in the diagram, to a certain height, h.

By using laws of Physics, he can calculate the velocity of the pellet when it hits the apple (i.e. the impact speed). The mass of the pellet is 1,0 g and the mass of the apple is 100g.

He repeats the experiment increasing the range by 5 m each time until the range is 20m.

9.1 State the principle of conservation of momentum (3)

9.2 State the principle of conservation of energy (3)

9.3 When he fired at the apple from point blank range, the height gained was 15 cm. calculate the speed of the apple plus pellet immediately after impact

(4)

9.4 Calculate the impact speed of the pellet (4)

9.5 Write a hypothesis for this experiment (1)

9.6 Identify the following variables for this experiment

9.6.1

The independent variable (1)

9.6.2

The dependent variable (1)

9.7 Suggest how he can measure the height to which the apple swings. Explain briefly. (3)

9.8 Pellet guns and catapults are dangerous weapons when used in towns or villages. The minimum kinetic energy to pierce skin is 2 J

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Mass (kg) Impact speed (m.s-1)

Catapult (stone) 0,01 15

Pellet gun (pellet) 0,001 150

Consider the following facts about a pellet gun and a catapult when fired from 20 m

9.8.1

Compare the momentum of the stone and the pellet (3)

9.8.2

Should either or both of these weapons be banned from use in towns and villages? Justify your answer with calculations and scientific facts

(7)

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QUESTION 10 DEEP SPACE EXPLOSIONS

The International Space Station (ISS) is a research facility in outer space. Air resistance is negligible in the ISS and everything in the ISS is at 'zero g'. A researcher on the ISS carries out an experiment in which he investigates the Principle of Conservation of Linear Momentum. An object with a mass of 1,6 kg is suspended inside a tank. The tank and its contents are free to move to the left, right, upwards, downwards, forwards or backwards. Initially, the object is stationary relative to the tank. The object explodes into two pieces, A and B, with mA = 600 g and mB = 1 kg. The pieces move apart horizontally until they stick to the end walls of the tank. Air resistance is negligible.

10.1 State the Principle of Conservation of Linear Momentum (3)

10.2 Piece A moves off with a momentum of 1,8 kg·m·s-1 to the left

10.2.1 What is the momentum of piece B? (2)

10.2.2 Calculate the velocity of Piece A immediately after the explosion. (5)

10.2.3 Which piece (A or B) will be the first to collide with an end wall of the tank? Justify your answer by using calculations

(9)

10.3 Immediately after the explosion:

10.3.1 What is the velocity of piece A relative to the velocity of piece B? (2)

10.3.2 How does the impulse on piece A compare with the impulse on piece B? Explain your answer

(4)

10.4 After the object explodes into the two pieces, the researcher continues to watch the tank and its contents for several minutes. Describe what was observed during this time

(3)

10.5 Read the passage below and consider the evidence for and against the cost of space exploration. Construct a reasoned argument in which you provide an answer to the question:

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Should we spend vast amounts of money on space research and exploration?'

Structure your answer using the framework below:

A I think that … (2)

B The evidence to support this idea is … (2)

C Arguments against me are … (2)

D I would counter these arguments by … (2)

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Unit 3: VERTICAL PROJECTILE MOTION

MULTIPLE CHOICE

1.1 Consider the sketch below that shows a man throwing a Javelin vertically upwards from a height “y” metres above the ground.

Which of the statements given below regarding its motion is INCORRECT?

A At its highest point its velocity is zero.

B At its lowest point its velocity is maximum.

C Its acceleration is 9.8ms-2 downwards towards the ground

D Its displacement is zero. (2)

2 An objects of mass m free-falls (from rest)for 1s covering a distance “Y” metres. What is the distance(m) covered by the object after 5s.

A Y

B 4Y

C 25Y

D 16Y (2)

1.3 A ball is thrown vertically upwards into the air. Ignore the effects of friction. The NET FORCE acting on the ball when the ball is at its highest point is ...

A zero

B equal to the weight of the ball

C less than the weight of the ball

D greater than the weight of the ball. (2)

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1.4 A ball of putty of mass m falls vertically towards the ground from a height “h” metres and comes to rest. Which of the position-time graphs below describes

1.5 The velocity versus time graph below represents the movement of an object under the influence of gravitational force.

The displacement of the object in time 3t is …

A 2vt

B zero.

C-

32vt

D vt. (2)

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Long questions:

Question 1

A girl fires an arrow upwards from the top of a cliff. The arrow leaves the bow at 20 m.s–1 and strikes the ground at 30 m.s–1, as shown below. Ignore the effects of air resistance.

Calculate:

1.1 the height ‘h’ that the arrow was shot from. (4)

1.2 the time that it takes for the arrow to reach the ground. (4)

[8]

Question 2

A hot air balloon is moving upward with a velocity of 5 m.s–1 . A person inside the balloon then throws a ball upward with a velocity of 7 m.s–1 relative to the balloon. Ignore the effects of air resistance. If the ball was 70 m above the ground when thrown upward, calculate:

The time taken for the ball to reach its highest point. (4)

The height of the ball above the ground at this point. (5)

Sketch a v-t graph showing the motion of the air balloon and the ball on the same set of axes.

(4)

[13]

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Question 3

A boy throws a ball vertically into the air from the top of a building. The ball strikes theground after 4,08 s. The velocity-time graph below represents the entire motion of the ball. Ignore the effects of air friction.Use the graph below to answer the questions that follow.

3.1 Explain what is meant by a projectile. (2)

3.2 What is the magnitude and direction of the acceleration of the

ball at time 1,02s?

(2)

3.3 Calculate the displacement of the ball. (4)

3.4 Sketch a position versus time graph for the entire motion of the ball.

Indicate the following on the graph:

• Initial position

• Maximum height

• Final position

• Time (t) values

(4)

[12]

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Question 4

The velocity-time graph below represents the motion of the ball from the instant it is dropped until after it bounces for the first time. The time interval between bounces is ignored. THE UPWARD DIRECTION IS TAKEN AS POSITIVE.

USE INFORMATION FROM THE GRAPH TO ANSWER THE QUESTIONS THAT FOLLOW.

4.2 Calculate the height above the ground from which the ball was dropped. (4)

4.3 Calculate the:

4.3.1 Time at the point P indicated on the graph (2)

4.3.2 Maximum height the ball reaches after the first bounce (3)

4.3.3 Distance between the ball and hot air balloon(ascending at 5.88ms-1 at t=0s)) when the ball is at its maximum height after the first bounce

(4)

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Question 5

The position-time graph below shows the motion of a ball starting from rest at an initial height of 80m with respect to the ground.

5.1 Describe the motion of the ball for a time of 1.28s. (2)

5.2 Calculate the velocity of the ball as it strikes the ground. (4)

5.3 If the ball is in contact with the ground for 0,25s, calculate the value of t2. (2)

5.4 Calculate the velocity at which the ball leaves the ground. (3)

5.5 Sketch a Velocity-time graph to show the entire motion of the ball. Your graph should include all relevant time and velocity values.

(4)

[15]

Unit 4: Work Energy and Power

Multiple Choice Questions (MCQ)

Question 1

1.1 Which ONE of the following equations represents the principle of the conservation of mechanical energy?

A △EK = △EP

B △EP = -△EK

C △EK + △EP - Wnc = 0

D △EP - △EP = Wnc (2)

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1.2 Peter pushes a lawnmower with a constant velocity of 1,5 m.s-1 . He applies a force of 40,5 N to the handle of the mower which makes an angle of 300 with the horizontal lawn.

The total friction force on the lawnmower is 35 N. If he pushes the lawnmower for 10 m the work done by Peter on the lawnmower is approximately:

A 405 J

B 350 J

C 300 J

D 202 J (2)

A cyclist pedals at a constant speed of 15 m.s-1 on a straight level road for 20 seconds. If he applies a force of 35 N on the pedals and the whole force is transmitted to the wheels, the power exerted by him is:

A 700 watts

B 300 watts

C 525 watts

D 325 watts (2)

1.4 An object with mass m is lifted at a constant velocity v through a height of h meter. The magnitude of the net work done on the object is:

A 0

B mgh

C 1/2mv2

D mgh + 1/2mv2 (2)

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1.5 A block, with mass m, is sliding down a rough surface that makes an angle with the horizontal, through a distance x as indicated in the sketch below. The net work done on the block will increase if...

A a greater frictional force acts on the block.

B the mass of the block is decreased.

C the distance x is decreased.

D the angle is increased. (2)

STRUCTURED QUESTIONS

Question 2 (Gauteng preparatory 2014)

A cyclist pushes his bicycle of mass 6,1 kg up an incline with a force of 20 N. The bicycle is pushed from an initial velocity of 5 m s-1 up the incline. The road is inclined at 10° to the horizontal and the distance from A to B is 32 m as shown below.

The road surface exerts a force of friction of 11 N on the bicycle tyres.

2.1 Calculate the work done by the cyclist on the bicycle. (3)

2.2 Use the work-energy theorem and calculate the magnitude of the velocity of the bicycle at 32 m.

(5)

2.3 Explain why frictional forces are regarded as non-conservative forces. (2)

[10]

Question 3 (Sowetan revision)

An electrical motor drives a turbine that pumps water vertically upwards from a dam to a reservoir 50m above the dam. The pump delivers 1 200 kg water in 2 minutes and the water is delivered at 12 m.s-1 at the reservoir.

Calculate the average power of the electric motor (7)

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32 m

10°

20N

Question 4 (Limpopo preparatory 2014)

A windmill is used on a farm to pump water out of a well that is 37 m deep. The water flows past point A, 37 m above the well to the dam with a constant velocity of 2 m•s-1.

4.1 Calculate how much energy is necessary to pump 90 kg of water out of the well to point A. (4)

4.2 It is necessary to pump 90 kg of water per minute. What is the maximum power that the windmill must produce?

(3)

4.3 Farmer wants to modernise the farm. The farmer decides to buy a 0,5 kW petrol water pump.

4.3.1 Will the petrol water pump be able to produce the required power? (YES or NO) (1)

4.3.2 Why would you advise the farmer to rather use a windmill instead of a petrol water pump?

(1)

[9]

Question 5 (Limpopo preparatory 2014)

A man pushes a crate, of mass 10 kg, up a rough surface inclined at 200 to the horizontal, with a 100 N force parallel to the surface.

The crate is pushed 5 m up the surface with an initial speed of 1,5 m.s–1. The coefficient of kinetic friction between the crate and surface is 0,4.

5.1 Draw a labelled free body diagram to show all the forces acting on the crate. (4)

5.2 Calculate the work done by gravity. (3)

5.3 Calculate the:

5.3.1 energy lost due to friction. (6)

5.3.2 work done by the man in pushing the crate up the surface. (1)

5.4 State the Work Energy Theorem in words. (2)

5.5 Use the Work Energy Theorem to calculate the magnitude of the final velocity of the crate after it has been pushed 5 m up the surface.

(2)

25

20 20

0

[20]

Question 6 (Gauteng preparatory 2015)

A container of mass 120 kg, hanging from a steel cable attached to a crane is accelerated vertically upwards from rest through a height of 12 m, as shown in the diagram below. The container reaches a maximum speed of 5 m.s–1 after being lifted through a height of 12 m.

6.1 Draw a labelled free body diagram showing all the forces acting on the container as it is accelerated upwards. (3)

6.2 If the tension in the cable is 800 N, calculate the work done by the cable to move the container to a height of 12 m. (3)

6.3 State the Work Energy Theorem in words. (2)

6.4 Use Energy Principles to calculate the work done on the container by friction while it is moving to a height of 12 m. (4)

6.5 Name ONE non – conservative force acting on the container as it is lifted. (1)

[13]

Question 7 (DBE FEB/MARCH 2016)

A constant force F, applied at an angle of 20o above the horizontal, pulls a 200 kg block, over a distance of 3 m, on a rough, horizontal floor as shown in the diagram below.

The coefficient of kinetic friction, μk, between the floor surface and the block is 0,2.

7.1 Give a reason why the coefficient of kinetic friction has no units. (1)

7.2 State the work-energy theorem in words. (2)

7.3 Draw a free-body diagram indicating ALL the forces acting on the block while it is being pulled. (4)

7.4 Show that the work done by the kinetic frictional force (Wfk) on the block can be written

as Wfk = (-1 176 + 0,205 F) J. (4)

26

of motion direction

m 21

AFTER BEFORE

m3 o20

F

kg200 o20 F

kg200

Rough floor

7.5 Calculate the magnitude of the force F that has to be applied so that the net work done by all forces on the block is zero. (4)

[15]

QUESTION 8 (DBE 2005 HG)

Learners at a school are given a task to determine the resistance offered by a liquid when a ball moves through it. Antara and Esha design a pendulum, consisting of an iron ball, mass 1,5 kg, attached to a light, inelastic string, and they allow this pendulum ball to swing through the liquid as shown.

The ball is released from point A, 60 cm above its lowest point of swing, C. It enters the liquid at point B, 20 cm above its lowest point. The two learners observe that the ball passes point C and comes to a stop at D, a point below the surface of the liquid before swinging back.

Ignore the effects of air resistance as well as the insignificant rise in the level of the liquid. The string remains straight throughout the motion.

8.1 State, in words, the principle of conservation of mechanical energy. (3)

8.2 Determine the kinetic energy of the ball when it enters the liquid at point B. (5)

8.3 The ball moves up to point D during its first swing as indicated in the diagram. Calculate the work done by the liquid on the ball, from point B to point D. (6)

[14]

27

cm 12

1,5 kg

cm 60

cm 20

D

C

B

A

Wave Sound and Light

Unit 1: Doppler Effect

QUESTION 1 ( EC-SEPTEMBER 2014)

An ambulance approaches an accident scene at a constant velocity. The siren of the ambulance emits sound waves with a constant, unknown frequency. A detector at the scene measures the frequency as 1,07 times the frequency of the siren.

1.1 State the DOPPLER EFFECT for sound in words. (2)

1.2 Calculate the speed at which the ambulance approaches the accident scene. Use the speed of sound in air as 340 m•s-1.

(5)

1.3 Explain, in terms of wave motion, why the frequency detected by the detector is higher than the frequency of the source.

(2)

1.4 State TWO uses of the Doppler flow meter in humans. (2)

1.5 A line in a hydrogen spectrum has a frequency of 7,55 x 1014 Hz when measured in a laboratory. The same line in the light of a star has a frequency of 7,23 x 1014 Hz.

Is this star moving TOWARDS or AWAY from the Earth? Explain your answer

(2)

[13]

QUESTION 2 (GP 2014-SEPTEMBER)

2.1 Keenan standing at the top of the Leaning Tower of Pisa accidentally drops his cell phone when it starts ringing at a frequency of 497 x 103 Hz. The height of the tower is 56 m.

2.1.1 Calculate the speed of the cell phone at a height of 18 m by using the law of conservation of mechanical energy.

(4)

Nerisse standing at the bottom of the tower hears the phone ringing as it falls towards her. Ignore the effects of air friction.

2.1.2 Calculate the frequency of the sound observed by Nerisse when the phone is at the height of 18 m above ground. Take the speed of sound in air as 340 m⋅s-1

(4)

2.1.3 Explain in terms of wavelength and frequency of sound why Keenan who is at the top of the tower, observes a lower frequency of sound than the value calculated in QUESTION 2.1.2.

(3)

2.1.4 How will the frequency of sound observed by Nerisse compare at a height of 18 m to that at 3 m? Write only HIGHER, LOWER or STAYS THE SAME

(1)

28

2.2 Speed cameras determine the speed of a car by measuring the signal of a radio wave reflected by the car.

2.2.1 Explain why the speed camera cannot measure the speed of the car accurately at the moment the car passes the camera.

(1)

2.2.2 What is the speed of the radio wave in air? Give a reason for your answer. (2)

[15]

QUESTION 3 (LP 2014 SEPTEMBER)

The siren of a stationary fire truck emits sound waves of frequency 1800 Hz. A car, travelling on a straight horizontal road at a constant speed of 30 m.s-1, passes the fire truck and continues at the same constant speed.

3.1 Name the medical instrument that makes use of the Doppler Effect. (1)

3.2 How does the pitch of the siren, heard by the driver of the car, change

when the car is moving: (State only increase, decrease or remain the

same)

3.2.1 Towards the fire engine? (1)

3.2.2 Away from the fire engine? (1)

3.3 Calculate the frequency detected by the driver as the car moves towards the fire truck. (Take the speed of sound in air as 330 m.s-1)

(5)

3.4 Sketch a graph to show how the frequency of the siren changes as a function of time as the driver approaches and then passes the fire truck. (No numerical values are required)

(3)

[11]

QUESTION 4 (MP 2014 SEPTEMBER)

A whale swims directly towards a stationary submarine at 8 m·s-1. The sonar system of the submarine has a frequency of 23 000 Hz. Take the speed of the sonar wave in sea water as 1435 m.s-1.

4.1 Define the Doppler effect. (2)

4.2 How does the frequency that the whale observes compare to the frequency sent out by the submarine? Write down only HIGHER, LOWER or STAYS THE SAME.

(1)

4.3 Calculate the frequency of the sound wave heard by the whale. (4)

The Doppler-effect is also used to monitor the movement of remote stars. During such a study of a star it was observed that the absorption line of red light moved to 688 nm. On the earth the absorption line of red light is observed at 653 nm.

4.4 Is the remote star moving NEARER TO or FURTHER AWAY from the earth? (4)

29

Give a reason for your answer.

[11]

QUESTION 5 (LP 2015 SEPTEMBER)

5.1 Humpback whales and bottlenose dolphins emit sound waves that range from 0,2 to 150 kHz as they travel through water. A scientist immerses a frequency meter under water to determine the frequency of the sound that a dolphin emits. The scientist finds that the frequency meter registers a frequency of 50 kHz as the dolphin approaches him at a constant speed and 49 kHz as it moves away from him at the same constant speed.

5.1.1 State the Doppler Effect in words. (2)

5.1.2 If the speed of sound in water is 1560 m.s-1, calculate the actual frequency of the sound made by the dolphin.

(8)

5.1.3 Hence, determine the speed at which the dolphin is moving. (2)

5.2 Briefly explain how an emission spectrum and an absorption spectrum

are formed.

(2)

[14]

QUESTION 6 (FS 2015 SEPTEMBER)

Light emitted from distant stars demonstrates the phenomenon known as red shift.

6.1 Explain how the phenomenon known as red shift can be used to explain an expanding universe.

(2)

6.2 A submarine can use the Doppler effect to detect the speed of ship.

A submarine at rest and just below the surface of the water, detects the

frequency of a moving ship as 437 Hz, 0,985 times the actual frequency of

the sound emitted by the ship. The speed of sound in water is 1470 m·s-1.

6.2.1 Is the ship moving away from or towards the submarine? Give a reason for your answer.

(2)

6.2.2 Calculate the speed of the ship. (5)

6.3 Name two applications of the Doppler effect in Medical Science. (2)

[11]

30

QUESTION 7 (MP 2015 SEPTEMBER)

A man mounts a siren, which produces a constant frequency of 800 Hz, on the roof of his car. He drives at a constant speed up and down a straight road while a stationary learner measures the observed sound

At a certain stage of the journey, the learner obtains the following pressure-time graph of the sound wave:

7.1 What is the period of the detected sound wave? (1)

7.2 Calculate the frequency of the detected sound wave. (3)

7.3 State the Doppler-effect in words. (2)

7.4 Calculate the speed of the moving car. Take the speed of sound in air as 340 m·s-1. (5)

7.5 While the car is stationary, the frequency of the siren is changed to 900 Hz. Will the wavelength of the detected sound wave INCREASE, DECREASE or REMAIN THE SAME? Explain the answer.

(3)

[14]

31

Unit 2: PHOTOELECTRIC EFFECT

MULTIPLE CHOICE QUESTIONS

QUESTION 1

1.1 Monochromatic blue light is incident on a metal surface as shown in the circuit diagramdrawn below. The intensity, I, of the incident blue light is gradually INCREASED.

Which ONE of the following graphs could represent the kinetic energy (EK), of the photoelectrons, ejected by the metal surface, as a function of the intensity (I)?

A

Ek

I

B

I

C

Ek

I

D

Ek

I

(2)

32

µA

1.2 If a light is passed through a cold, diluted gas, the atoms of the gas absorb photons at certain …

A frequency and form an absorption spectrum.

B frequency and form a line emission spectrum.

C velocity and form an absorption spectrum.

D velocity and form a continuous spectrum. (2)

1.3 A bundle of GREEN light is incident on the cathode of a photo-electric cell. The milli- ammeter registers a current in the circuit. The green light is removed and BLUE light with a lower intensity is incident on the same photo-electric cell. How does the amount of photo-electrons released per second and the speed of the photoelectrons compare when BLUE light is used?

Amount of

photoelectrons per second

Speed of photoelectrons

A Decreases Decreases

B Increases Decreases

C Decreases Increases

D Stays the same Increases (2)

1.4 Light of a certain frequency is incident on a metal surface and photoelectrons are emitted from the surface. If the INTENSITY of the same light is increased the

A kinetic energy of the emitted photoelectrons increases.

B kinetic energy of the emitted photoelectrons decreases.

C number of photoelectrons emitted per second increases.

D number of photoelectrons emitted per second decreases. (2)

1.5 When a light wave from a distant star is analysed it is found that this wave is “red-shifted”. This confirms that the wave experienced a…

A decrease in wavelength and increase in frequency.

B decrease in wavelength and decrease in frequency.

C increase in wavelength and decrease in frequency.

D increase in wavelength and increase in frequency. (2)

1.6 A line emission spectrum is formed when electrons in an atom, that moves from …

A higher to lower energy levels, emit energy as light.

B higher to lower energy levels, absorb light energy.

33

C lower to higher energy levels, emit energy as light.

D lower to higher energy levels, absorb light energy. (2)

[12]

Question 2 (Mpumalanga September 2015)

In the diagram below, photons of ultraviolet light with energy 5,6 x 10-19 J is incident on the cathode of a photo cell and causes photo-electrons to be emitted from the metal surface.

The threshold (cut-off) frequency of the cathode of the photocell is 7,2 x 1014Hz.

2.1 Which property of light is illustrated by the photo-electric effect (1)

2.2 Define the term threshold (cut-off) frequency in words. (2)

2.3 Calculate the maximum kinetic energy of the emitted photo-electrons. (3)

2.4 The brightness of the ultraviolet light is now increased. How will this change affect each following? Only write down INCREASES, DECREASES or REMAINS THE SAME.

2.4.1 The kinetic energy of the emitted photoelectrons. (1)

2.4.2 The reading on the ammeter. (1)

2.5 The ultraviolet light source is now replaced with a light source of wavelength 622 nm. Will this light source be able to eject photo-electrons from the cathode of the photo-cell? Support your answer with a calculation. (4)

[12]

34

QUESTION 3 (Limpopo Sept. 2015)

The diagram represents a photocell. When the metal surface is exposed to electromagnetic radiation, photoelectrons are ejected. The collector collects the photoelectrons and the sensitive ammeter indicates the presence of a tiny current. The

metal has a work function of 3,5 x 10-19 J.

3.1 Name the frequency that is associated with work function (1)

3.2 Calculate the maximum kinetic energy of an ejected photoelectron when the incident radiation is 429 nm. (5)

3.3 The intensity of the incident radiation is doubled but the wavelength is kept constant. State the effect that this has on each of the following: (only write INCREASE, DECREASE or REMAIN THE SAME as your answer):

3.3.1 the energy of each photon . (1)

3.3.2. the maximum kinetic energy of each photoelectron (1)

3.3.3 the current in the photocell . (1)

3.4 At a certain frequency and intensity of radiation, the ammeter shows a current of 3,2 x

10-7 A. Calculate the number of photoelectrons that reach the collector in 4 seconds. (4)

[13]

Question 4 (Eastern Cape Sept. 2015)

Learners in a physics class perform an experiment using a photo cell to investigate the relationship between photo electrons emitted and the frequency of the incident light.

35

A graph is plotted of the maximum kinetic energy (Ek) against the frequency of

the incident light. When the straight line graph is extrapolated, it intercepts the x- axis

at fo = 4,29 x 1014 Hz.

4.1 Write an investigative question for this investigation. (2)

4.2 What is the frequency, f, in the graph called? (1)

4.3 Calculate the frequency, fx, in the graph. (5)

4.4 Draw a sketch-graph of the kinetic energy of the photo-electrons (on the y-axis) versus the intensity of the incident light. (No values needed on the graph.) (3)

[11]

QUESTION 5 (DBE Nov 2012)

During an investigation, light of different frequencies is shone onto the metal cathode of a photocell. The kinetic energy of the emitted photoelectrons is measured. The graph below shows the results obtained.

36

Kin

etic

ene

rgy

(J) E1

Graph of kinetic energy versus frequency

37

5.1 For this investigation, write down the following:

5.1.1 Dependent variable (1)

5.1.2 Independent variable (1)

5.1.3 Controlled variable (1)

5.2 Define the term threshold frequency. (2)

5.3 Use the graph to obtain the threshold frequency of the metal used as cathode in the photocell.

(1)

5.4 Calculate the kinetic energy at E1 shown on the graph. (4)

5.5 How would the kinetic energy calculated in QUESTION 11.4 be affected if light of higher intensity is used? Write down only INCREASES, DECREASES or REMAINS THE SAME.

(1)

[11]

QUESTION 6 (DBE Feb/Mar. 2011.)

6.1 A group of learners performs an investigation to compare the effect of two types of radiation on the emission of photoelectrons from zinc. They place a zinc plate on top of the disc of a negatively charged electroscope. Ultraviolet and red light are shone alternately onto the zinc plate as shown below, with the electroscope fully charged in each case.

They record the following observations:

RADIATION OBSERVATION

Ultraviolet light Gold leaves collapse

Red light No effect on the deflection of gold leaves

6.1.1 Write down an INVESTIGATIVE QUESTION for this investigation. (2)

38

radiation

gold leaves

electroscope

----- - -

zinc platedisc

6.1.2

6.1.3

Explain the observation made for ultraviolet light.

What conclusion can be drawn from this investigation?

(3)

(2)

6.1.4 The following safety precaution is printed on the ultraviolet light source:

OVEREXPOSURE TO ULTRAVIOLET LIGHT IS A HEALTH RISK

Name ONE health risk associated with overexposure to ultraviolet light. (1)

QUESTION 7 (DBE Nov 2009)

The photo-electric effect has many practical applications. A photocell, such as the one below used in burglar alarm systems, is one such application.

Ultraviolet light of wavelength 100 nm is used to illuminate the photocell. When a person interrupts the ultraviolet beam, the sudden drop in current activates a switch, which sets off the alarm.

7.1 Define the term threshold frequency. (2)

7.2 How will an increase in intensity of the ultraviolet light influence the ammeter reading? Write only INCREASES, DECREASES or REMAINS THE SAME. Explain your answer. (3)

7.3 The work function of the metal used as a cathode in the photocell is 8,7 x 10-

39

A

Anode

Cathode

Electrons

Ultraviolet light beam

19 J. Calculate the velocity at which the electrons are emitted. (6)

[11]

QUESTION 1 (Exemplar 2014 Q 11)

Graph P below shows how the maximum kinetic energy of electrons emitted from the cathode of a photoelectric cell varies with the frequency of the incident radiation

Graph of maximum kinetic energy versus frequency

1.1. Define the term work function. (2)

1.2. Calculate the:

1.2.1 Work function of the metal used as cathode in the photocell (3)

1.2.2 Velocity of photoelectrons emitted when the frequency of the

incident light is 8 x 1014 Hz

(5)

The photocell is now replaced with another one in which the work function of the cathode is TWICE that of the metal in the first cell.

40

Max

imum

kin

etic

ene

rgy

(x 1

0-19

J)

Graph P

12

8

4

10 3020

0Frequency (x 10 14 Hz)

The maximum kinetic energy versus frequency graph, Q, for this cathode is now drawn on the same set of axes as graph P.

1.3.1 How will the gradient of graph Q compare to that of graph P?

Write down GREATER THAN, SMALLER THAN or EQUAL TO. Explain the answer.

(2)

1.3.2 What will the value of the x-intercept of graph Q be? Explain how you arrived at the answer.

(2)

QUESTION 3 (2016 Feb-March Q11)

An investigation was conducted to determine the effects of changes in frequency AND

intensity on the current generated in a photoelectric cell when light is incident on it.

The apparatus used in the investigation is shown in the simplified diagram below.

Incident light

µA

The results of the experiment are shown in the table below.

EXPERIMENT FREQUENCY (Hz) INTENSITY (Cd) CURRENT

A 4,00 x 1014 10 0B 4,50 x 1014 10 0C 5,00 x 1014 10 0D 5,01 x 1014 10 20E 5,01 x 1014 20 40F 6,50 x 1014 10 30

11.1 Define the term work function. (2)

The threshold frequency for the metal used in the photocell is 5,001 x 1014 Hz.

41

11.3 Define the term threshold frequency. (2)

11.4 Calculate the maximum speed of an emitted electron in experiment F. (5) In experiments D and E, the current doubled when the intensity was doubled at the

same frequency.

11.5 What conclusion can be made from this observation? (2)[12]

ELECTROSTATICS

QUESTION 1

1.1 The sketch below shows two small metal spheres, A and B, on insulated stands carrying charges of magnitude q and 2q respectively. The distance between the centres of the two spheres is r.

Sphere A exerts a force of magnitude F on sphere B. What is the magnitude of the force that sphere B exerts on sphere A?

A

B

C

12 F

F

2F

(2)

42

BA 2q

r

q

D

4F

43

1.2 A small test charge +q is placed exactly half way between two identical negatively charges, X and Y, each with a charge + Q, as shown below.

The test charge +q will

A remain where it is

B move towards X

C move towards Y

D move vertically downward

(2)

1.3 Two charged spheres V and W are located on a straight line. X, Y and Z are three points on the same straight line. The positions of points X, Y and Z are as indicated and the direction of the NET electric field at points X, Y and Z is shown in the diagram below.

Which ONE of the following combinations represent the charges on each of the spheres V and W?

Charge of V Charge of W

A Positive Positive

B Neutral Positive

C Negative Negative

D Positive Negative (2)

44

•X Y

WZ

V

+ Q +q + Q

X d d Y

1.4 Three small identical spheres, A, B and C is charged as shown in the diagram. The distance between sphere B and C is x.

+16 μC -4 μC +4 μC

A B C

x

For sphere B to experience no resultant electrostatic force, the distance between A and B must be …

A

B

C

D

¼ x.

½ x.

2 x.

4 x. (2)

45

QUESTION 2 (DBE NOV 2011.)

Two metal spheres, P and T, on insulated stands, carry charges of +3 x 10-9 C and

-6 x 10-9 C respectively.

The spheres are allowed to touch each other and are then placed 1,5 m apart as shown below.

2.1 In which direction will electrons flow while spheres P and T are in contact? Write down only FROM P TO T or FROM T TO P.

(1)

2.2 Calculate the net charge gained or lost by sphere P after the spheres have been in contact

(3)

.

Calculate the number of electrons transferred during the process in QUESTION 2.2. (2)

A third sphere R, carrying a charge of -3 x 10-9 C, is NOW placed between P and T at a distance of 1 m from T. Calculate the net force experienced by sphere R as a result of its interaction with P and T. (6)

[12]

46

QUESTION 3 (SCE 2015)

Two identical neutral spheres, M and N, are placed on insulating stands. They are brought into contact and a charged rod is brought near sphere M.

When the spheres are separated it is found that 5 x 106 electrons were transferred from sphere M to sphere N.

3.1 What is the net charge on sphere N after separation? (3)

3.2 Write down the net charge on sphere M after separation. (2)

The charged spheres, M and N, are now arranged along a straight line, in space, such that the distance between their centres is 15 cm. A point P lies 10 cm to the right of N as shown in the diagram below.

3.3 Define the electric field at a point. (2)

3.4 Calculate the net electric field at point P due to M and N. (6)

[13]

47

QUESTION 4 (MP TRIAL 2015)

Sphere A has a charge of +4 µC and is placed in an insulated cylinder.

A second identical but oppositely charged sphere B, mass 500 g,hangs at rest at a distance r, directly above A. Sphere B is attached to a scale as shown below.

4.1 Draw the net electric field pattern due to spheres A and B. (3)

4.2 State Coulomb’s Law in words. (2)

4.3 Draw a labelled force diagram of all the forces acting on sphere B. (3)

4.4 What is the magnitude of the net upward force that acts on sphere B? (1)

4.5 Calculate the distance r between spheres A and B. (6)

48

20N

19 N

r

+ 4 μC

B

A

- 4 μC

[15]

QUESTION 5 (FS TRIAL 2015)

The diagram below shows two identical insulated metal spheres. Spheres P an Q each carry a charge of 6 nC.

+6 nC +6 nC

P Q

20 cm

5.1 Define Coulomb’s Law in words. (2)

5.2 Draw the electric field pattern due to the two spheres P and Q. (3)

5.3 Calculate the magnitude of the electrostatic force between spheres P and Q.

(4)

A third sphere, R, of charge -2 nC is now placed at a position relative to the other spheres and a chosen point X as shown in the diagram below.

+6 nC +6 nC -2 nC

P Q R X●

20 cm 20 cm 10 cm

5.4 Calculate the net electric field at point X due to spheres P, Q and R. (6)

[15]

49

QUESTION 6 (DBE EXEMPLER 2014)

Three small, identical metal spheres, Q1, Q2 and Q3, are placed in a vacuum. Each sphere carries a charge of – 4 μC. The spheres are arranged such that Q2 and Q3 are each 3 mm from Q1 as shown in the diagram below.

6.1 State Coulomb's law in words. (2)

6.2 Draw a force diagram showing the electrostatic forces exerted on Q1 by Q2 and Q3. (2)

6.3 Calculate the net force exerted on Q1 by Q2 and Q3. (8)

[12]

QUESTION 7

Two identical metal spheres, A and B, on insulated stands are placed with their centres 10 cm apart as shown in the sketch below. Sphere A has a charge of –15 nC while sphere B carries an unknown positive charge. P is a point 2 cm away from the centre of A, as shown in the sketch.

The NET electric field at point P is 3,943 x 105 N.C–1 to the left.

7.1 Define the term electric field at a point. (2)

7.2 Draw the resultant electric field pattern due to the charges on A and B. (2)

7.3 Calculate the magnitude of the unknown charge on sphere B. (7)

7.4 Sphere B is removed. State whether the electric field at P, due to the charge on sphere A, will INCREASE, DECREASE or REMAIN THE SAME. (1)

[12]

50

2 cm 8 cm

P

BA

QUESTION 8 (DBE MARCH 2015)

Two identical negatively charged spheres, A and B, having charges of the same magnitude, are placed 0,5 m apart in vacuum. The magnitude of the electrostatic force that one sphere exerts on the other is 1,44 x 10-

1 N.

8.1 State Coulomb's law in words. (2)

8.2 Calculate the:

8.2.1 Magnitude of the charge on each sphere (4)

8.2.2 Excess number of electrons on sphere B (3)

8.3 P is a point at a distance of 1 m from sphere B.

8.3.1 What is the direction of the net electric field at point P? (1)

8.3.2 Calculate the number of electrons that should be removed from sphere B so that the

net electric field at point P is 3 x 104 N·C-1 to the right. (8)

[18]

QUESTION 9 (DBE GRADE 11 NOV 2014.)

Two point charges of +2 μC and +3 μC are placed a distance of 0,2 m apart. P is a point on

the line joining the two charges, a distance of x m from the 3 μC charge such that

the net electric field at point P is zero.

9.1 Define the term electric field at a point in words. (2)

9.2 Calculate the distance x. (7)

A -4 μC charge is now placed a distance of 0,1 m from the +3 μC charge as shown in the sketch below.

51

9.3 Calculate the magnitude of the electrostatic force experienced by the +3 μC charge due to

the presence of the other two charges. (5)

[14]

QUESTION 10 (MARCH EXAM 2016.)

Two identical spherical balls, P and Q, each of mass 100 g, are suspended at the same point

from a ceiling by means of identical light, inextensible insulating strings. Each ball carries

a charge of +250 nC. The balls come to rest in the positions shown in the diagram below.

10.1 In the diagram, the angles between each string and the vertical are the same.

Give a reason why the angles are the same. (1)

10.2 State Coulomb's law in words. (2)

10.3 The free-body diagram, not drawn to scale, of the forces acting on ball P is shown below.

Calculate the:

10.3.1 Magnitude of the tension (T) in the string (3)

10.3.2 Distance between balls P and Q (5)

52

[11]

QUESTION 11 (DBE NOV 2015)

A very small graphite-coated sphere P is rubbed with a cloth. It is found that the sphere acquires

a charge of + 0,5 μC.

11.1 Calculate the number of electrons removed from sphere P during the charging process. (3)

Now the charged sphere P is suspended from a light, inextensible string. Another sphere, R, with a

charge of – 0,9 μC, on an insulated stand, is brought close to sphere P. As a result sphere P

moves to a position where it is 20 cm from sphere R, as shown below. The system is in

equilibrium and the angle between the string and the vertical is 7o.

11.2 Draw a labelled free-body diagram showing ALL the forces acting on sphere P. (3)

11.3 State Coulomb's law in words. (2)

11.4 Calculate the magnitude of the tension in the string. (5)

ELECTRIC CIRCUITS

Question 1

1.1 Which ONE of the following graphs best represent the relationship between the electrical 1.2 power and the current in a given ohmic conductor?

A B

W W

53

TOTAL RESISTANCE TOTAL CURRENTA Decreases Decreases

B Increases Increases

C Decreases Increases

D Increases Decreases

C D

W W

(2)

1.2 Three identical resistors X, Y and Z are connected as shown in the circuit below.

Y X

Z

If the power in X is P, then the power in Y is …

A P B ½P

C ¼P D 2P

1.3 Consider the circuit diagram below.

R1

R2

R3

Which ONE of the following correctly describes the change in total resistance and total current when switch S is closed?

(2)

54

1.4 The unit of measurement of THE RATE OF FLOW OF CHARGE in a conductor is …

A watt. B volt.

C ampere. D coulomb. (2)

1.5 A set of identical light bulbs are connected as shown in the circuit diagrams below. The internal resistance of the battery is negligible.

In which ONE of these circuits will the light bulbs glow the brightest?

A B

C D

55

1.6 Which ONE of the circuits below can be used to measure the current in a conductor X and the potential difference across its ends?

A A B A

X V V

X

C D A

X A V X V

(2)

1.7 Which ONE of the following graphs best represents the relationship between the electrical power and the current in a given ohmic conductor?

A P B P

I I

C P D P

I I

(2)

56

A1 A2 A3 A

A 1,25 1,25 0 2,5

B 1,6 0,8 0,1 2,5

C 0,75 0,75 0 1,5

D 1 0,5 0 1,5

1.8 Three light bulbs, X, Y and Z with resistances R, 2R and R respectively, are connected in a circuit as shown below. The battery has negligible internal resistance.

When switch S is closed, all the bulbs light up. The reading on ammeter A

is 2,5 A.

X Y Z

●

S ● A1 A2 A3

A

Which ONE of the following correctly describes the readings on the ammeters

(in amperes) when bulb Z burns out?

(2)

Three identical light bulbs are connected in a circuit as shown below. The resistances of the battery and connecting wires can be ignored.

V1 V2

S •

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Which ONE of the following statements is CORRECT when switch S is closed?

The reading on V1 is …

A half that on V2 .

B equal to that on V2 .

C twice that on V2 .

D three times that on V2 . (2)

Question 2 (2008 additional exemplar)

Four resistors of different resistances are connected in a circuit as shown below. The battery has an emf of 30V and an internal resistance of 2Ω. The resistance of the connecting wires is negligible. 

 2.1 Define the concept emf of a battery. (2)2.2 Calculate the potential difference between points X and Y. (7)

Question 3 (2008 additional exemplar)

A group of learners are requested to investigate the relationship between electric current and potential difference. Before conducting the investigation they have to plan and design a suitable experiment. 

The learners approach you to assist them with the planning and design of the investigation. Make a group of learners are requested to investigate the relationship between electric current and potential difference. Before conducting the investigation they have to plan and design a suitable experiment. 

The learners approach you to assist them with the planning and design of the investigation. Make use of the layout below to help them with the planning and design of the investigation. Use of the layout below to help them with the planning and design of the investigation.

58

  3.1 What is the investigative question for this investigation? (2)

3.2 Write down a possible hypothesis for this investigation. (2)

3.3 Write down one variable that learners should control in this investigation (1)

3.4 List ALL the apparatus that the learners will need for this investigation. (3)

3.5 Draw a circuit diagram that they can use to assemble the apparatus. (3)

3.6 Describe, in not more than four lines, how the learners must use this apparatus to take the required measurements. (3)

Question 4 (2008 Prep KZN)

Consider the electric circuit below and answer the questions that follow.

4.1 Calculate the magnitude of the current. (6)

MULTIPLE CHOICE QUESTIONS.

QUESTION 1

1.1 Which one of the following phrases correctly explains how a generator works? It works…

A by converting electrical energy to mechanical energy.

B by using the motor effect.

C by using Lenz’s law.

D by using electromagnetic induction.

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1.2 A simplified diagram of a generator is shown below.

Coil ABCD rotates …

A clockwise.

B anticlockwise.

C clockwise, reaches the vertical position and then reverses its direction.

D anticlockwise, reaches the vertical position and then reverses its direction.

1.3 A current is induced when a conductor is moved between two magnets as shown in the diagram below.

The magnitude of induced current can be increased by:

I. using stronger magnets.II. moving the conductor at higher speed between the magnets.III. placing the 2 magnets further away from each other.

Which of the above statements are true?

A I and II only

B II and III only

C I and III only

D I, II and III

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1.4 Two strong bar magnets are arranged with their poles O and Q facing each as shown in the diagram below. A current – carrying conductor carries conventional current into the plane of the paper when placed between the poles of two magnets.

If the force on the conductor is towards R then:- A O and Q are both north poles. B Q and O are both south poles. C Q is a north pole and O is a south pole. D O is a north pole and Q is a south pole. (2)

1.5 The diagram below shows the variation in emf produced by a generator:

If the armature of the generator is rotated at twice the speed how will the emf and the period shown by the graph change?

1.6 The magnet in the following diagram is moving away from the solenoid. The induced current flows through the resistor in a direction from …

61

A Q to R

B R to Q

C Q to R and then from R to Q

D R to Q and then from Q to R (2)

1.7 In the graph below, the solid line represents how the emf, produced by a simple generator, changes with time. The dotted line shows the output of the same generator after a change was made to the generator.

Which change is made to produce the result as shown?

A The amount of turns in the coil is doubled.

B The speed of rotation is doubled.

C A split ring commutator is added.

D the strength of the magnets is doubled.

62

QUESTION 2 (LP SEPT 2015)2.1 The simplified sketch below represents the structure of the motor of a cordless drill.

2.1.1 Name the electrical component in the above motor that ensuresthat the coil rotates in one direction only. (1)

2.1.2 Identify the polarity of magnets A and B if the coil rotates in an anticlockwise direction and the current flows in the coil in the direction indicated in the sketch. (2)

2.2 Another drill operates with alternating current. The maximum current output of thisdrill is 10,6 A. A graph of the potential difference output of the drill against time is

63

shown below.

2.2.1 Calculate the rms current the drill draws when operating. (3)

2.2.2 Hence, calculate the average power generated by the drill. (3)

2.2.3 Is the power generated by the drill at time t1 a MAXIMUM or MINIMUM? (1)[10]

QUESTION 3 (WC SEPT 2015).

In a simple generator a coil is rotated anti-clockwise in a uniform magnetic field. The diagram below shows the position at the instant the coil lies parallel to the magnetic field.

3.1 Name the law on which a generator operates. (1)

3.2 Name component P. (1)

64

3.3 What is the function of component P? (1)

3.4 Determine the direction of the current in segment XY when the coil is in the position shown above. Only write down X to Y OR Y to X. (1)

3.5 Is the induced potential difference in the coil illustrated above about to increase or to decrease? Explain your answer by referring to the change in magnetic flux as the loop rotates from the horizontal to the vertical position. (3)

3.6 Draw a sketch graph of emf in the external circuit against time for one complete rotation of the armature coil, starting with the coil in the position shown. (2)

[9]

QUESTION 4 (EC SEPT 2015).

The light bulb shown below is able to operate either with direct current or with alternating current. It displays its optimum operating conditions and the accompanying graph displays the current type that is being used.

4.1 Is the bulb operating with direct current, or alternating current? (1)

4.2 Explain the meaning of 100 W. (1)

4.3 Calculate the rms current in the bulb when it is connected in a circuit. (4)

4.4 Explain why ESKOM prefers AC instead of DC for long distance transmission of electricity. (2)

[8]

QUESTION 5 (FS SEPT 2015).

The diagram below shows a coil that is rotated through a magnetic field.

65

5.1.1 Name the principle demonstrated in the above diagram? (1)

5.1.2 The maximum emf is generated at position A of the rotation cycle. Give an explanation for this observation. (2)

5.1.3 Name one structural difference between a DC and AC generator. (2)

5.1.4 Use the positions indicated in the diagram above and sketch a graph of current versus position for one complete rotation of a DC generator. (Indicate the positions A, B, C and D on the graph.) (4)

5.2 When an AC supply is connected to a lamp, it lights up with the same brightness as it does when connected to a 18 V battery (DC source).

The power dissipated by the lamp is equal to 60 W.

5.2.1 What is the rms voltage of the AC supply? (1)

5.2.2 Calculate the peak current delivered by the AC source. (5)

[15]

QUESTION 6 (NC SEPT 2015).

The diagram below represents and electrical machine and P is a split ring commutator.

66

6.1 Identify the type of electrical machine and write down the energy conversion that

takes place in this electrical machine. (2)

6.2 Explain the function of the component P. (2)

6.3 The split ring commutator is replaced by slip rings. Which ONE of the following

voltage-time graphs (Graph A or Graph B) corresponds with the above change?

Explain the answer. (3)

6.4 The light bulb shown in the circuit dissipates energy of 6 J per second. An identical light bulb is connected in parallel to it. Calculate the rms current in the circuit under the new conditions. Assume the emf remains unchanged. (5)

[12]

67

QUESTION 7 (GPSEPT 2015).

A learner built the following simple generator based on a dynamo used to power bicycle headlights. He used the generator to demonstrate that he could use mechanical energy to generate electrical energy.

7.1 Is this a DC or an AC generator? Give a reason for the answer. (3)

7.2 How will the learner know that electrical energy is produced? (1)

7.3 Explain how this generator is able to produce electrical current when there is no electrical connection between the rotating magnet and the copper coil.

(3)

7.4 List TWO changes that can be made to the generator to INCREASE the BRIGHTNESS of the globe.

(2)

A generator (dynamo) used to power a light on a bicycle needs an average power of 6 W and a potential difference of 12 Vrms.

7.5 Calculate the maximum current that can flow through the globe. (4)

QUESTION 8 (DBE F EB/ MAR 2011)

AC generators at coal-fired power stations supply most of the electrical energy needed in our country.

8.1 State ONE structural difference between an AC and a DC generator. (2)

A certain AC generator (alternator) produces a peak current (Imax) of 6,43A

when connected to an electrical heater of resistance 48,4 Ω.

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8.2 Calculate the rms current (Irms) produced by the generator. (3)

8.3 Calculate the peak voltage (Vmax) output of the generator. (5)

8.4 Draw a sketch graph of potential difference versus time for this AC generator. Clearly label the axes and indicate Vmax on the potential difference axis. (2)

8.5 To meet energy demands in the country, the government plans building nuclear power stations. State ONE environmental advantage of the generation of electricity in nuclear power stations over coal-fired power stations. (1)

QUESTION 9 (NW SEPT 2015)

69

70

QUESTION 10 (NW SEPT 2015)

71

QUESTION 11(MP SEPT 2015)

The diagram below represents a simplified alternating current (AC) generator.

11.1 State the energy conversion that takes place in an AC generator. (1)

11.2 A 2 Ω resistor is attached to the AC generator. Calculate the maximum current that flows through the resistor if the resistor dissipates an average power of 80 W. (5)

A television is switched on for an average of 142 hours per month. The television is rated 1 200 W; 220 V.

11.3 If the ESKOM tariff is R1, 25 per unit, calculate the monthly cost of the electricity used by the television. (2)

[8]

72

MATTER AND MATERIAL

MULTIPLE CHOICE QUESTIONSQUESTION 1

1.1 Which ONE of the following compounds is an aldehyde?A. CH3COCH3

B. CH3CH2CHOC. CH3CH2COOHD. CH3CH2CH2OH

(2)

1.2 The addition of hydrogen to an alkene is known as ...A. Hydration.B. Cracking.C. Hydrogenation.D. Hydrohalogenation.

(2)

1.3 Which ONE of the following compounds has the highest boiling point?A . CH3CH3

B . CH3CH2CH3

C . H3CH2CH2CH3

D . CH3CH2CH2CH2CH3

(2)

1.4Which ONE of the following compounds has dipole-dipole force between its molecules?A . EthanalB . EthaneC . EtheneD . Ethyne

(2)

1.5 Which ONE of the following compounds is an aldehyde?

A. PentanalB. Pentan-2-olC. Pentan-2-oneD. Ethyl propanoate

(2)

1.6 Consider the reaction represented by the equation below:CH3CHCH2 + H2 → CH3CH2CH3

This reaction is an example of …

(2)

A. Hydration.B. Dehydration.C. Substitution.D. Hydrogenation.

73

1.7 Consider the structural formula of a compound below. (2)

Which ONE of the following pairs of reactants can be used to

prepare this compound in the laboratory?

A. Propanoic acid and ethanolB. Propanoic acid and methanolC. Ethanoic acid and propan-1-olD. Methanoic acid and propan-1-ol

1.8 Which ONE of the following statements is CORRECT? Alkenes ...A . Have the general formula CnH2n+2.B . Are unsaturated hydrocarbons.C . Readily undergo substitution reactions.D . Have one triple bond between two carbon atoms.

(2)

1.9 The following equation represents the cracking of a hydrocarbon at high temperature and pressure:

C11H24 → 2C2H4 + Y + C4H10

Which ONE of the following is the IUPAC name of product Y?

(2)

A. Prop-1-eneB. PropaneC. EtheneD. Ethane

1.10 When 2-chlorobutane is strongly heated in the presence of concentrated sodium hydroxide, the major product formed is …

(2)

A. But-1-ene.B. But-2-ene.C. Butan-1-ol.D. Butan-2-ol.

74

PAPER TWO

CHEMESTRY

75

UNIT 1: NOMENCLATURE

QUESTION 2 (GP TRIALS 2015 )

Consider the organic compounds represented by the letters A to F

A CH3CH2CH2CHO B 2-methylbut-2-ene

C

D

E

F

2.1 Write down the LETTER that represents the following:

2.1.1 An addition polymer (1)

2.1.2 A compound that is a functional isomer of compound D. (1)

2.2 Write down the IUPAC name of the following:

2.2.1 Compound A (1)

2.2.2 Compound E (2)

2.3 Compound B is one of the reatants needed to produce comound E.

Write down the…

2.3.1 NAME or FORMULA for the other reactant needed for this reaction.

(1)

2.3.2 structural formula of compound B. (3)

1.3.3 type of reaction that takes place (1)

1.4 The table contains a compound that occurs as a result of condensation Polymerisation

1.4.1 Define the term condensation polymerisation. (2)

1.4.2 Write down the letter that represents the compound that is a (1)

76

condensation polymer.

[13]

QUESTION 3 (WC Winelands Trial Exam 2015)

Consider the organic compounds represented by the letters A to G :

3.1 Define the term hydrocarbon. (2)

3.2 Write down the LETTER that represents...

2.2.1 a chain isomer of compound A. (1)

2.2.2 a positional isomer of compound A. (1)

2.2.3 A functional isomer of compound D. (1)

3.3 Define the term structural isomer. (2)

3.4 Write down the IUPAC name of compound B. (2)

3.5 Write down the molecular formula of compound C. (1)

3.6 Write down the structural formula of compound E. (2)

3.7 Write down the structural formula for the functional group of compound C.

(1)

3.8 Write down the IUPAC name of the compound that contains a carboxyl group.

(1)

3.9 Is compound A SATURATED or UNSATURATED? Give a reason for your answer.

(2)

3.10 Write down the name of the homologous series to which compound (1)

77

B belongs.[17]

QUESTION 4: (KwaZulu Natal Trials 2014)

Consider the following representation of organic molecules A to F listed in the table below:

4.1 Write down the letter that represents a compound that:

4.1.1 Is an aldehyde (1)

4.1.2 Is a saturated hydrocarbon (1)

4.1.3 Has a general formula CnH2n-2 (1)

4.2 Write down the homologous series to which each of the following

compounds belongs:

4.2.1 A (1)

4.2.2 B (1)

4.2.3 F (1)

4.3 Write down the:

4.3.1 Molecular formula of the next compound in the same

homologous series as compound C.

(1)

4.3.2 Structural formula of compound E (2)

4.3.3 IUPAC name of compound B (2)

4.3.4 Functional group of compound D (1)

[12]

QUESTION 4 (GP Trials 2014)

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Consider the following compounds and answer the questions below:

5.1.1 To which homologous series does compound F belong? (1)

5.1.2 Which compound is an alkyne? (1)

5.1.3 Give the IUPAC name for compound E. (1)

5.1.4 Compound C is one of the reactants needed to produce compound B. Give the IUPAC NAME for the other reactant needed for the production of compound B.

(1)

5.1.5 Write down an equation, using structural formulae to represent the formation of compound B

(4)

5.1.6 Write down the structural formula of a functional isomer of compound F.

(2)

5.1.7 Compound A can burn in excess oxygen. Using molecular formulae, write a balanced equation for the reaction

(3)

5.1.8. Name the type of reaction that takes place in QUESTION 5.1.7

(1)

5.2 There are two chain isomers for the organic compound with molecular formula C4H10.5.2.1 Define the term chain isomer. (2)

5.2.2. Write down the structural formulae of the two chain isomers and also give their IUPAC names.

(4)

5.2.3 Which ONE of the isomers mentioned in QUESTION 5.2.2 has the highest Boiling point?

(1)

5.2.4 Explain the difference in the boiling points of the chain isomers.

(3)

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[24]

QUESTION 6 (DBE Feb-Mar 2016)

Consider the organic compounds represented by the letters A to C below.

6.1.1 Name of the homologous series to which compound C belongs

(1)

6.1.2 IUPAC name of compound A (3)6.1.3 Structural formula of a tertiary alcohol that is a structural isomer of compound B

(2)

6.2 An alcohol and methanoic acid are heated in the presence of concentrated sulphuric acid to form an ester.6.2.1 What is the role of the concentrated sulphuric acid in this reaction?

(1)

6.2.2 Write down the NAME or FORMULA of the inorganic product formed

(1)

The ester contains 6,67% hydrogen (H), 40% carbon (C) and 53,33% oxygen (O). The molar mass of the ester is 60 g·mol-1.Use a calculation to determine its:6.2.3 Empirical formula (5)6.2.4 Molecular formula (3)Write down the:6.2.5 Structural formula of methanoic acid (1)6.2.6 IUPAC name of the ester (2)

[19]

80

QUESTION 7 (DBE November 2015)

The letters A to D in the table below represent four organic compounds

Use the information in the table to answer the questions that follow.

7.1 Write down the:7.1.1 Letter that represents a ketone (1)7.1.2 Structural formula of the functional group of compound C. (1)7.1.3 General formula of the homologous series to which compound A belongs.

(1)

7.1.4 IUPAC name of compound A (3)7.1.5 IUPAC name of compound B (2)

7.2 Compound D is a gas used in cigarette lighters.7.2.1 To which homologous series does compound D belong? (1)7.2.2 Write down the STRUCTURAL FORMULA and IUPAC NAME of a structural isomer of compound D.

(4)

7.2.3 Is the isomer in QUESTION 7.2.2 a CHAIN, POSITIONAL or FUNCTIONAL isomer?

(1)

7.3 Compound D reacts with bromine (Br2 ) to form 2-bromobutane.Write down the name of the:7.3.1 Homologous series to which 2-bromobutane belongs (1)7.3.2 Type of reaction that takes place (1)

[16]

QUESTION 7 (DBE FEB/MAR 2015)

The letters A to F in the table below represent six organic compounds.

81

8.1 Write down the:8.1.1 NAME of the functional group of compound B (1)

8.1.2 Homologous series to which compound C belongs (1)8.1.3 Type of polymerisation reaction that produces compound F (1)

8.2. Write down the IUPAC name of:8.2.1 The monomer used to prepare compound F (1)8.2.2 Compound C (2)8.2.3 Compound D (2)

8.3 Write down the NAME or FORMULA of each product formed during thecomplete combustion of compound D

(2)

8.4 Write down the structural formula of:8.4.1 Compound B (2)8.4.2 A CHAIN ISOMER of compound A (2)

8.5 A laboratory assistant uses bromine water to distinguish between compounds D and E. She adds bromine water to a sample of each in two different test tubes. She observes that the one compound decolourises the bromine water immediately, whilst the other one only reacts after placing the test tube in direct sunlight. Write down the:8.5.1 Letter (D or E) of the compound that will immediately decolourise the bromine water

(1)

8.5.2 Name of the type of reaction that takes place in the test tube Containing compound D

(1)

8.5.3 Structural formula of the organic product formed in the test tube containing compound E

(2)

[18]

QUESTION 9 (Limpopo TRIAL 2014)

The letters P to W in the table below represent eight organic

compounds.

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9.1 Write down the:

9.1.1 Letter that represents a SECONDARY alcohol. (1)

9.1.2 Name of the functional group of compound W. (1)

9.1.3 Name of the homologous series to which compound V belongs. (1)

9.1.4 IUPAC name of compound R (2)

9.1.5 NAME of the polymer formed from compound S, if compound S is

the monomer of a certain organic compound.

(1)

9.1.6 Balanced equation, using MOLECULAR FORMULAE, for the

combustion of compound T in excess oxygen.

(3)

9.1.7 IUPAC name of compound P (2)

9.1.8 General formula of the homologous series to which compound Q belongs

(1)

A few drops of fresh reddish-brown bromine water are added to

compound S in a test tube.

9.2 Describe what will be observed in the test tube. (1)

9.3 Use structural formulae to write down a balanced equation for the

reaction that takes place in the test tube

(4)

[17]

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UNIT 2: ORGANIC REACTIONS QUESTION 1 ( FREE STATE SEPTEMBER 2015)

Propane is used as fuel in heating appliances, cooking equipment and vehicles. It burns in air to release large amounts of energy

1.1 Using molecular formulae, write down a balanced equation for the complete combustion of propane in oxygen.

(3)

The flow diagram below shows how propane can be used as starting material in the preparation of other compounds.

1.2 Write down the type of reaction (ADDITION, SUBSTITUTION or ELIMINATION) represented by:1.2.1 A (1)1.2.2. B (1)1.2.3. C (1)

1.3 In reaction B, compound X is converted to a haloalkane. Write down the:

1.3.1 IUPAC name of compound X (1)

1.3.2 Balanced equation for the formation of the major product in reaction B, using structural formulae

(4)

1.4 Reaction C takes place in the presence of a strong base. Write down:

1.4.1 TWO reaction conditions needed (2)

1.4.2 The IUPAC name of the alcohol produced (2)

1.5 During a reaction, the alcohol in QUESTION 4.4.2 is converted to compound X. Write down the FORMULA of the inorganic reactant needed.

(1)

[16]

84

PropaneCompound X

CH2 CHCH3

HaloalkaneAlcohol

Reaction A

Reaction C

Reaction BHydrogen bromide

CH3CH=CH2 H2O P

2-bromopropane

SATURATEDHYDROCARBON

Polymer Y

QUESTION 2 LIMPOPO SEPTEMBER 2014

The flow diagram below shows the preparation of different organic compounds using propene (CH3CH = CH2) as starting material.

The flow diagram below shows the preparation of different organic compounds using propene (CH3CH = CH2) as starting material.

2.1 NAME the process that converts the saturated hydrocarbon to propene. (1)

2.2 Use structural formulae to write down a balanced chemical equation for the reaction between propene and water to produce compound P.

(4)

2.3 Write down the IUPAC name of compound P. (1)

2.4 Compound P can also be obtained from 2-bromopropane.

Write down the:

2.4.1 type of reaction that converts 2-bromopropane to P (1)

2.4.2. Conditions under which the conversion can occur.(2)

2.5 Write down the:

2.5.1 NAME of polymer Y (1)

2.5.2 TYPE OF polymerisation that produces Y. Choose from (1)

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ADDITION or CONDENSATION

[11]

QUESTION 3 WESTERN CAPE WINELANDS SEPTEMBER

3.1 The flow diagram below shows the preparation of two organic compounds, using propene as one of the reactants.

3.1.1 Use structural formulae to write down a balanced chemical

equation for the reaction between propene and water to produce

compound P.

(4)

3.1.2 Write down the IUPAC name of compound P. (1)

3.1.3 Compound P can also be obtained from 2-bromopropane. Write

down the:

(a) Type of reaction that converts 2-bromopropane to P. (1)

(b) Conditions under which the conversion can occur (1)

3.2 A learner is preparing an ester using methanol (molecular formula: CH4O) and ethanoic acid (molecular formula: C2H4O2). The balanced chemical equation for this reaction is given below:

CH4O + C2H4O2 → C3H6O2 + H2O

3.2.1 What type of reaction is represented by the equation above? (1)

3.2.2 Write down the NAME or FORMULA of the catalyst needed in

this reaction

(1)

3.2.3 When 50 g of methanol fully reacts with excess ethanoic acid, it

produces 68,88 g C3H6O2. Calculate the percentage purity of the

methanol.

(5)

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87

QUESTION 4 (GAUTENG SEPT 2015)

The flow diagram shows the various chemical reactions of haloalkanes. P, Q, and R represent the reaction types

Write down the type of reaction represented by:

4.1.1 Q (1)

4.1.2 R (1)

For the reaction P, write down the following:

4.2.1 The structural formula of the alcohol formed. (2)

4.2.2 The IUPAC name of the alcohol formed (1)

4.3 In reaction S, propene reacts with compound X to form 2-bromopropane.

Write down the:

4.3.1 NAME of compound X (1)

4.3.2 Balanced chemical equation using structural formula (4)

[10]

88

QUESTION 5: WC METRO SOUTH SEPT 2015

Reaction 1 uses a dilute solution of NaOH while Reaction 2 uses a concentrated solution of NaOH dissolved in hot ethanol.

5.1 Consider reaction 1:

5.1.1 X is the major product formed. Draw the structural formula of

X.

(2)

5.1.2 Name the type of reaction. (1)

5.2 Consider reaction 2:

5.2.1 Draw the structural formula of the major product, Y. (2)

5.2.2. Name the type of reaction (1)

5.3 Consider reaction 3:

5.3.1 Name the type of elimination reaction. (1)

5.3.2. Give the condensed structure of product Z (2)

5.4 Compound Z is a monomer of a polymer used to make plastic bags

5.4.1. Write down the name and condensed structural formula of this polymer.

(3)

5.4.2 Describe the type of polymerisation that forms the polymer in QUESTION 5.4.1

(2)

[14]

89

QUESTION 6 (DBE/FEB-MAR 2016)

The flow diagram below shows different organic reactions using CH2 = CH2 as the starting reactant. X, Y and Z represent different organic compounds

6.1 During Reaction 1, CH2 = CH2 undergoes polymerisation to form compound Y.

For this reaction, write down the

6.1.1 Type of polymerisation (1)

6.1.2 NAME of compound Y (1)

6.2 For Reaction 2, write down the:

6.2.1 IUPAC name of compound X (2)

6.2.2 Type of addition reaction of which this is an example (1)

6.3 During Reaction 3, compound X reacts with excess hot water. Write down the:

6.3.1 STRUCTURAL FORMULA of compound Z (2)

6.3.2 NAME or FORMULA of the INORGANIC product (1)

6.4 Reaction 4 is an addition reaction

6.4.1 Is C2H6 a SATURATED or an UNSATURATED compound? Give a reason for the answer.

(2)

6.4.2 Write down the NAME or FORMULA of the INORGANIC reactant needed for this reaction.

(1)

6.4.3 Using molecular formulae, write down a balanced equation for the complete combustion of C2H6

(3)

[14]

90

QUESTION 7 DBE/FEB-MAR 2015

In the flow diagram below, but-1-ene is used as starting material in the preparation of compound A

7.1 Is but-1-ene a SATURATED or UNSATURATED compound? Give a reason for the answer.

(2)

7.2 Compound A is the major product formed in reaction 1.Write down the:7.2.1 Structural formula of compound A (2)7.2.2 Type of reaction that takes place (1)

7.3 For compound B, write down the:7.3.1 IUPAC name (2)7.3.2 Structural formula of the positional isomer (2)

7.4 For reaction 3, write down:7.4.1 TWO reaction conditions needed (2)7.4.2 The type of reaction that occurs (1)7.4.3 A balanced equation, using molecular formulae (3)

[15]

QUESTION 8 DBE/NOV 2014

The flow diagram below shows the preparation of an ester using prop-1-ene as a starting reagent. P, Q, R and S represent different organic reactions.

8.1 Write down the type of reaction represented by8.1.1 Q (1)8.1.2 R (1)

8.2 For reaction P write down the:8.2.1 Type of addition reaction (1)

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8.2.2 Balanced equation using structural formulae (3)8.3 Write down the structural formula of the haloalkane formed in reaction Q (2)

8.4 In reaction S propan-1-ol reacts with ethanoic acid to form the esterFor this reaction write down the:8.4.1 Name of the reaction that takes place (1)8.4.2 FORMULA or NAME of the catalyst needed (1)8.4.3 Structural formula of the ester formed (2)8.4.4 IUPAC name of the ester formed (2)

8.5 The propan-1-ol formed in reaction R can be converted to prop-1-ene. Write down the FORMULA or NAME of the inorganic reagent needed

(1)

[15]

QUESTION 9 DBE/ FEB-MAR 2014

The flow diagram below shows the steps that a learner follows to convert but-1-ene to but-2-ene

9.1 Write down the structural formula of the functional group of but-1-ene. (1)9.2 Compound X is formed when but-1-ene reacts with HCℓ(g).

9.2.1 Name the type of reaction that takes place (1)9.2.2 Write down the structural formula of compound X (2)

9.3 Compound X is converted to alcohol Z.9.3.1 Name the type of reaction that takes place. (1)9.3.2 Write down the NAME or FORMULA of another reactant needed for this reaction.

(1)

9.4 Compound Z is converted to but-2-ene in the presence of concentrated sulphuric acid.9.4.1 Is compound Z a PRIMARY, SECONDARY or TERTIARY Alcohol?

(1)

9.4.2 Name the type of reaction that takes place. (1)9.4.3 What is the role of sulphuric acid in this reaction? (1)

9.5 Another learner discovers that but-2-ene can be prepared using thefollowing incomplete reaction below.Compound X + (a) → but-2-ene + (b) + (c)Write down the:9.5.1 Type of reaction that takes place (1)9.5.2 Conditions needed for this reaction to take place (2)

92

A CH3CH2COOH CH3CH2CH2CH2CH3 CH3CH2CH2CH2OHB CH3CH2CH2CH2OH CH3CH2CH2CH2CH3 CH3CH2COOHC CH3CH2CH2CH2CH3 CH3CH2CH2CH2OH CH3CH2COOHD CH3CH2CH2CH2CH3 CH3CH2COOH CH3CH2CH2CH2OH

9.5.3 FORMULAE of the reactant and products represented by each of the letters (a), (b) and (c) respectively (3)

(3)

[15]

.UNIT 3: PHYSICAL PROPERTIES

QUESTION 1

1.1. In which ONE of the following options are the three compounds arranged in order of increasing (lowest to highest) boiling points?

(2)

1.2. Which one of the following organic compounds will have the LOWESTboiling point?A Propanoic acidB Propan-1-olC Propan-2-olD Propanal.

(2)

QUESTION 2 (EC-TRIAL 2015)

2.1 Define the term vapour pressure. (3)

2.2 The table below shows the vapour pressure values of three alkanes

Name Vapour pressure (kPa at 20 °C)ethane 3 750

propane 843butane 204

2.2.1 Fully explain why the vapour pressure DECREASES from ethane to butane (3)

2.2.2 Which of the alkanes will be the most difficult to ignite at room temperature?

(1)

2.3.1 Predict whether ethanol will have a HIGHER or a LOWER vapour pressure than ethane.

(1)

2.3.2 Fully explain the answer to QUESTION 2.3.1. (3)

[8]

.

93

94

QUESTION 3: (FS-TRIAL 2015)

The table below shows the boiling points of six organic compounds, represented by the letters A to F.

COMPOUND BOILING POINT (°C)

A Methane -162

B Ethane -89

C Propane -42

D Methanol 65

3.1

Consider compounds A to C.

3.1.1 What is the physical state (SOLID, LIQUID or GAS) of propane at 45 °C? (1)

3.1.2 Write down the general formula of the homologous series to which these compounds belong.

(1)

3.1.3 What is the trend in boiling points from compound A to compound C? Write down INCREASES or DECREASES. Fully explain this trend.

(4)

3.2

The boiling points of compounds C and E are compared. Fully explain the difference in boiling points by referring to the TYPE of intermolecular forces present in each of these compounds.

(2)

3.3

How will the vapour pressure of compound E compare to that of compound F? Write down HIGHER THAN, LOWER THAN or EQUAL TO. Give a reason for the answer by referring to the boiling points of the compounds.

(3)

[11]

.

QUESTION 4 (MP-TRIAL 2015)

A learner investigates the relationship between the structural isomers of pentane and their boiling points. The results obtained were recorded as shown below:

COMPOUND MOLECULAR FORMUA

BOILING POINT (ºC)

Pentane C5H12 36

2-methylbutane C5H12 28

2,2-dimethylpropane

C5H12 10

95

4.1 Define the term structural isomer. (2)

4.2 Name the homologous series to which the compounds belong. (1)

4.3 For this investigation write down the:

4.3.1 Dependent variable (1)

4.3.2 Independent variable (1)

4.3.3 Conclusion that can be drawn from the above results (2)

4.4 Refer to MOLECULAR STRUCTURE, INTERMOLECULAR FORCES and ENERGY needed, to explain your conclusion in QUESTION 4.3.3.

(4)

4.5 What precaution should the learners take when carrying out the experiment? Give a reason.

(2)

[13]

QUESTION 5 (NC-TRIAL 2015)

The table below shows the boiling points of four organic compounds, represented by the letters A to D, of comparable molecular mass.

Compound Molecular mass Boiling point (°C)

A Butane 58 0

B Propanal 58 49

C Propan-1-ol 60 97

D Ethanoic acid 60 118

5.1 Compound A is used as a fuel in gas lamps

5.1.1 How will the vapour pressure of an ISOMER of compound A compare to

that of compound A? Write down HIGHER THAN, LOWER THAN or

EQUAL TO. Refer to MOLECULAR STRUCTURE, SPECIFIC

INTERMOLECULAR FORCES and the ENERGY needed to explain the

answer.

(4)

5.1.2 Using molecular formulae, write down the balanced equation for the

combustion of the compound with THREE carbon atoms, belonging to the

same homologous series as compound A, in excess oxygen.

(3)

5.1.3 The boiling point of compound B is higher than that of compound A. Give a

reason for this observation by referring to the intermolecular forces between

(3)

96

the two compounds.

5.2 Consider the boiling points of compounds C and D.Give a reason for the difference in boiling points by referring to the intermolecular forces present in EACH of these compounds.

(3)

[13]

QUESTION 6 (GP-TRIAL 2015)

6.1

An organic compound with a molecular formula of C4H6 has two positional isomers.

6.1.1 Define the term positional isomer. (2)

6.1.2 Write down the structural formulae of TWO positional isomers of C4H6 and also give their IUPAC names

(4)

6.2

Heptane can undergo cracking to form an alkene with three carbon atoms and a branched four-carbon alkane.

6.2.1 Write down a balanced equation using structural formulae. (3)

6.2.2 Write down the IUPAC names of the products formed in this reaction. (2)

6.3

An investigation is conducted to determine the boiling points of different types of homologous series. The table below shows the boiling points of compounds from different homologous series.

Organic compound Boiling point (°C)Propane -42Propan-1-ol 97Propanoic acid 141

6.3.1 Define the term boiling point. (2)

6.3.2 Explain the difference in boiling points of propan-1-ol and propanoic acid by referring to the TYPE of INTERMOLECULAR FORCES present in the compounds.

(3)

[16]

QUESTION 7 (WC-TRAIL -2015)

97

7.1

Alkanes are primarily used as fuels. Consider the energy values of

various compounds:

Fuel

Energy in kJ∙mol-1 Energy in kJ∙g-1

coal

39 3petrol (C8H18) 5

51048b

utane2

63645 methane

890 ?

7.1.1

Write a balanced equation for the complete combustion of butane using molecular formulae.

(3)

7.1.2

Make use of a calculation and determine which fuel releases more energy per unit mass (g): butane or methane.

(3)

7.1.3

Give one reason why coal is used as a fuel of choice in many

Industries despite its relatively low energy per mol ratio.

(1)

7.2

Consider the boiling points of the following alkanes:

Alkane Boiling point (OC) Molecular Mass (g.mol-1)Propane - 42 44

Methylpropane - 11,7 58

Butane - 0,5 58

Pentane 36 72

7.2.1

Explain why the boiling point of pentane is higher than that of butane.

Refer to structure, strength of intermolecular forces (IMF’s) and energy in your answer

(3)

7.2.2

Methylpropane is an isomer of butane. Explain why its boiling point is lower than that of butane despite having the same molecular mass.

(2)

7.2.3

Why is it important, when comparing the boiling points of butane and methylpropane, that the compounds have identical (very similar) molecular mass?

(1)

7.2.4

Which compound in the above table has the highest vapour pressure? (1)

98

[14]

QUESTION 8 (DBE NOV-2009)

The table below shows the results obtained during a practical investigation. Two experiments were performed to determine the boiling points of compounds from three different homologous series under the same conditions. Each letter A to F represents the organic compound written in the block next to it.

Experiment Organic compound

Molar mass

(g·mol-1)

Boiling point

(°C)

I

A CH3COOH 60,5 118

B CH3CH2CH2OH 60,1 97

C CH3CH2CHO 58,1 48

II

D CH3(CH2)2COOH 88,1 163

E CH3(CH2)3CH2OH 88,1 137

F CH3(CH2)3CHO 88,1 103

8.1

Name the homologous series to which each of the following pairs of compounds belong:

8.1.1 A and D (1)

8.1.2 B and E (1)

8.1.3 C and F (1)

8.2

Write down the IUPAC name for:

8.2.1 Compound C (1)

8.2.2 Compound E (1)

8.3

Formulate an investigative question for this practical investigation. (2)

8.4

Which other variable, apart from the conditions for determining boiling points, was kept constant?

(1)

99

8.5

What conclusion can be drawn from the results in Experiment II? (2)

8.6

Refer to intermolecular forces to explain the trend in boiling points, as shown in the table.

(3)

[13]

CHEMICAL CHANGE

UNIT 4: RATES OF REACTION

QUESTION 1 WESTERN CAPE WINELANDS (SEPT 2015)

A learner investigates the factors that influence the rate of reaction. He

adds 50g of Zn granules to 500cm3 hydrochloric acid (HCℓ) with a

concentration of 2mol.dm-3. Assume that the zinc is completely covered by the hydrochloric acid. The hydrochloric acid has a temperature of

20oC. The change in the concentration of HCℓ during this reaction is shown in the graph below:

The balanced reaction is shown as follows:

Zn(s) + 2HCℓ(aq) → ZnCl2(aq)+H2(g)

1.1 Write down TWO observations for this experiment. (2)

1.2 Define the term reaction rate. (2)1.3 Calculate the average reaction rate for this reactionover45s. (4)1.4 How does the initial rate of the reaction change if each of the following changes

100

are made: Write only INCREASE, DECREASE or STAY THE SAME.1.4.1

Increase the temperature of the hydrochloric acid to30oC. (1)

1.4.2Use 600 cm3of the2mol∙dm-3hydrochloric solution instead of 500 cm3. (1)

1.4.3. Add copper sulphate as a catalyst. (1)

[11]

QUESTION 2 : EASTERN CAPE (Sept 2014)

Graph B below represents the Maxwell-Boltzmann energy distribution curve for a reaction mixture at a temperature of 300°C.Area X represents the number of molecules in the mixture that have enough kinetic energy for the reaction to take place.

2.1 Give a term for the “minimum energy needed for a reaction to take place ”,as indicated by Y

(1)

2.2 The temperature of the mixture is now increased to 500

2.2.1 Which ONE of graph A or C represents the distribution curve of the mixture at this higher temperature? Give a reason for the answer. (2)

2.2.2 Use the collision theory to explain how this increase in temperature will influence the rate of the reaction.

(4)

2.3 A catalyst is added to the mixture.

2.3.1 Write down the definition of a positive catalyst. (2)

2.3.2 How will the above-mentioned action affect the size of area X (shaded area)?

Write down only INCREASES, DECREASES or REMAINS THE SAME. (1)

2.3.3 Explain your answer to QUESTION2.3.2. (2)

101

[12]

QUESTION 3 : EASTERN CAPE (SEPT 2015)

Learners use the reaction of a sodium thiosulphate solution (Na2S2O3) with a hydrochloric acid solution (HCℓ to investigate the factors which influence reaction rate.

The balanced equation for the reaction is:

Na2S2O3(aq) +2HCℓ(aq) H2O (ℓ) + SO2(g)+ 2NaCℓ(aq)+S(s)

The time lapse from the moment of mixing equal volumes of the two solutions until a certain degree of turbidity (sulphur precipitation formation) appeared is taken as a measure of the rate of the reaction.

102

3.1 Consider INVESTIGATION A:

3.1.1 For investigation A, name the:

(a) Dependent variable (1)

(b) Independent variable (1)

3.1.2 What conclusion can be drawn from the results of investigation A? (2)

3.1.3 Which ONE of the two reactants (Na2S2O3 or HCℓ) in experiment 1 of investigation A is the limiting reactant? Explain your answer.

(3)

3.2 Consider INVESTIGATION B:

Temperature

(°C)

Concentration ofNa2S2O3 (mol·dm-3)

Concentration ofHCℓ

(mol·dm-3)

Time

(s)Experiment4 20 0,5 0,5 40

Experiment5 30 0,5 0,5 20

Experiment6 50 0,5 0,5 10

3.2.1. In which experiment is the rate of the reaction the fastest? Give a reason for your answer.

(2)

3.2.2. Explain your observation in QUESTION 3.2.1. in terms of collision theory. (3)

[12]

QUESTION4 GAUTENG (Sept 2014)

The following apparatus was used by a group of learners in an investigation to find out how surface area affects the rate of reaction between solid magnesium metal and 100cm3 dilute sulphuric acid with a concentration of 1mol∙dm-3.

During the reaction the gas that forms is collected in the gas syringe which measures the volume of gas produced.

103

Temperature

(°C)

Concentration

ofNa2S2O3 (mol·dm-3)

Concentration

ofHCℓ (mol·dm-3)

Time

(s)Experiment1 20 0,5 0,5 40

Experiment2 20 0,9 0,5 25

Experiment3 20 1,4 0,5 15

The equation for the reaction is:

Mg(s) + H2SO4(aq) MgSO4(aq) +H2(g)

In EXPERIMENTI, 20g of magnesium, in the form of 5 small pieces, was used. In EXPERIMENTII, 20g of magnesium, in the form of one big piece was used. The learners performed the experiments and plotted a graph of their results for experiment one, which is represented below

4.1 Besides the mass and thevolume of the reactants, give ONE other variable that must be kept constant in this investigation

(1)

4.2 Name the dependent variable for EXPERIMENT I. (1)

4.3 Use the graph to calculate the average rate of the reaction (in cm3·s-1) for the first 30 seconds.

(3)

4.4 Will the rate of the reaction at 50s be GREATERTHAN, LESSTHAN or EQUAL TO that rate calculated in QUESTION 4.3?

(1)

104

100 cm3, 1.0 mol.dm-3

Sulfuric acid

Gas Syringe

Mg Ribbon

Volume of a gas (cm3)

time (s)

4.5 Give a reason for your answer in QUESTION 4.4. (1)

4.6 Predict how the gradient of EXPERIMENT II results would compare to EXPERIMENT I plotted above.

Write only INCREASE, DECREASE or NO CHANGE. (1)

4.7 Use the collision theory to explain, how the increase in surface area of the magnesium metal affects the rate of the reaction.

(3)

4.8 Calculate the mass of magnesium metal that remains after the reaction has stopped.

(5)

4.9 Catalytic converters are substances that are coated onto surfaces of car exhausts to act as positive catalysts.

Define a positive catalyst. (2)

[18]

QUESTION 9 (DBE-FEB/MAR 2016)

9.1 Define the term boiling point. (2)

9.2 What is the relationship between strength of intermolecular forces and boiling point?

(1)

The relationship between strength of intermolecular forces and boiling point is investigated using four organic compounds from different homologous series. The compounds and their boiling points are given in the table below.

COMPOUND BOILING POINT (°C)A Propane -42B Propan-2-one 56C Propan-1-ol 97D Propanoic acid 141

9.3 Refer to the TYPE and the STRENGTH of intermolecular forces to explain the difference in boiling points between:

9.3.1 Compounds A and B (3)

9.3.2 Compounds C and D (3)

9.4 Is compound B a GAS or a LIQUID at room temperature? (1)

[10]UNIT 4: CHEMICAL EQUILIBRIUM

QUESTION 1: GAUTENG (Sept 2014)

When a number of moles of X2(g) and Y2(g) are placed in an empty, closed 2dm3

105

container at 800°C,a reaction takes place and eventually reaches equilibrium according to the following equation:X2(g) + 3Y2(g) ↔ 2XY3

At equilibrium there is 0,4 mol∙dm-3 of Y2 and XY3 present. You are also given the following information for the reaction:

1.1 Calculate the initial number of moles of X2 and Y2 placed in the container. (9)

1.2 Is the forward reaction endothermic or exothermic? (1)

1.3 Explain your answer to QUESTION 1.2. (2)

1.4 What effect will be adding more Y2(g) at 800°C have on the following?

Answer only INCREASE, DECREASE OR STAYTHESAME.

1.4.1 The rate of the reverse reaction (1)

1.4.2 Concentration of X2(g) (1)

1.5 Which ONE of the following gases XY3 or X2 would be present in a higher concentration in the equilibrium mixture at400°C?

(1)

1.6 Explainyour answer to QUESTION 1.5 (2) [17]

QUESTION 2: EASTERN CAPE(Sept 2015)2.1 Solid potassium chromate (K2CrO4) is dissolved in water. In solution, the

chromate ions (CrO42-) reach equilibrium with the dichromate ions (Cr2O7

2-) according to the following balanced equation.2CrO4

2-(aq)+2H+

(aq)⇌ Cr2O72-

(aq)+ H2O(ℓ)

Yellow OrangeConcentrated nitric acid is now added to the equilibrium mixture2.1.1 Predict the change in colour (if any) that will be observed as the nitric

acid is added to the solution. ONLY Write down “Orange to Yellow”, “Yellow to Orange” or “No Change

(1)

2.1.2 Which ONE of the two ions (CrO42- or Cr2O7

2-) is more stable in a solution with a low pH?

(1)

When the temperature is increased gradually, it is observed that the 106

Temperature°C Kc400 0,8600 2,5800 4,0

colour of the solution changes to yellow.2.1.3 Is the forward reaction represented above exothermic or endothermic? (1)2.1.4 Explain the answer in QUESTION 2.1.3 by referring to Le Chatelier’s

principle.(3)

2.2 Five (5) moles of hydrogen gas and 5 moles of iodine vapour are sealed in a 2 dm3 vessel at a temperature of 600 K. The reaction reaches equilibrium according to the following balanced chemical equation:H2(g)+ I2(g) ↔2HI (g)

2.2.1 Calculate the concentration of the hydrogen iodide (HI) at equilibrium if the equilibrium constant, Kc, at 600 K is 0,36.

(8)

2.2.2 The pressure on the system is now changed. The graph below shows the changes in concentrations of the reactants and products as a result of this change.

Did the pressure INCREASE or DECREASE at t1?Briefly explain (3)[17]

QUESTION 3 : LIMPOPO (Sept 2015)

112,84 g of mercury(II) oxide is heated in a 250 cm3sealed container. The decomposition that takes place in the container is represented by the following equation:

2HgO(s)⇌2Hg(ℓ) + O2(g)∆H > 0

Equilibrium is reached at 650 ° C. Analysis shows that, at equilibrium, the mass of mercury(II) oxide (HgO) is 69,44 g.

3.1 For this reaction, a sealed container is classified as a CLOSED SYSTEM. Explain why this is so.

(2)

3.2 Calculate the equilibrium constant (Kc)at 650 ° C for this reaction. (9)

3.3The volume of the container is now decreased to 125 cm3while the temperature is KEPT CONSTANT. The system reaches a NEW equilibrium. How will each of the following be affected? Write down only INCREASES, DECREASES or REMAINS THE SAME.3.3.1 The number of moles of HgO(s) present in the NEW equilibrium mixture (1)

3.3.2 The value of the equilibrium constant (Kc) (1)

3.3.3 The concentration of O2(g)in the new equilibrium mixture. (1)

3.3.4. Use Le Chatelier’s Principle to explain the answer to QUESTION 3.3.1. (2)

[16]

107

QUESTION 4: EASTERN CAPE (Sept 2014)

The catalytic oxidation of ammonia is represented by the equation below:4NH3(g) +5O2(g)⇌4NO(g) + 6H2O(g)

2,0 mol of ammonia gas and 1,0 mol of oxygen gas are placed in a 2,0 dm3container at1000 kPa and allowed to reach equilibrium at1000 °C. At this temperature and pressure the amount of water vapour present is 0,6 mol.

4.1 Calculate the value of the equilibrium constant at this temperature. (8)4.2 Briefly explain the significance of the value obtained in QUESTION 6.1. (1)4.3 What effect will the addition of a platinum catalyst have on the yield of NO(g)at

the given temperature?Write down only INCREASE, DECREASE or REMAIN THE SAME. (1)

4.4 The pressure on the system is decreased by increasing the volume. Use Le Chatelier’s principle to explain how this change affects the yield of NO(g)

(3)

4.5 It is found that at a temperature of 500 °C the value of the equilibrium constant is greater than the value calculated in QUESTION 4.1. What is the sign of ∆H for the reaction mentioned above?

(1)

4.6 Explain your answer to QUESTION 4.5 (4) [18]

QUESTION 5: WESTERN CAPE Metro (Sept 2015)

The rapidly increasing human population is resulting in an ever-increasing demand for food. To meet this demand, farmers apply fertiliser to the same cultivated land each year.

5.1 Explain why farmers have to apply fertiliser to the same land EACH YEAR. (1)5.2 Write down ONE negative impact that over-fertilisation can have on humans (2)5.3 Sulphuric acid is an important substance used in the manufacture of fertilisers.

The equation below represents one of the steps in the industrial preparation of sulphuric acid2 SO2(g) + O2(g)⇌2SO3(g),∆H< 05.3.1 Name the industrial process used to prepare sulphuric acid. (1)5.3.2 Write down the NAME or FORMULA of the catalyst used. (1)5.3.3 Sulphur trioxide (SO3) is dissolved in oleum to make concentrated

sulphuric acid. Write down the formula of oleum.(1)

5.3.4 Write down the FORMULA of the fertiliser formed when sulphuric acid reacts with ammonia.

(2)

5.3.5 Sulphuric acid also plays a role in turning phosphates into superphosphates.(a) Explain why this process is necessary? (1)(b) Name one natural (organic) source of phosphates. (1)

5.4 The reaction represented in QUESTION 5.3 reaches equilibrium at 350OC in a 2dm3 closed containers. On analysis, it is found to contain 0,8mol SO2, 0,5mol O2 and 0,6mol SO3.

108

5.4.1 Explain what is meant by the term “equilibrium”. (2)5.4.2 How must the pressure in the container be changed to increase the

yield of SO3? Write only INCREASED or DECREASED.(1)

5.4.3 Explain your answer to QUESTION 5.4.2 in terms of Le Chatelier’sPrinciple

(2)

5.4.4 The temperature is now increased to 500OC and the reaction is allowed to reach equilibrium again at the new temperature. On analysis, it is found that 0,3 mol of SO2 is present in the container. Calculate the equilibrium constant at 500OC.

7

5.4.5 At which temperature will the Kc value will be greater: 350OC or 500OC?

2

[23]

QUESTION 6: FREE STATE (Sept 2014)The reaction represented by the equation below reaches equilibrium in a closed container at a certain temperature.

CS2(g)+ 3Cℓ2(g)⇌S2Cℓ2(g)+ CCℓ4(g)(∆H<0)6.1 Is the above equilibrium a HOMOGENEOUS or a HETEROGENEOUS

equilibrium? Give a reason for the answer.(2)

6.2 Initially1,2 moles of CS2(g) and 4 moles of Cℓ2(g) are injected into a 2 dm3 sealed

container. Analysis of the equilibrium mixture shows that 138,6g of CCℓ4(g) is present. Calculate the equilibrium constant (Kc) at this temperature.

(8)

6.3 The pressure is now decreased by increasing the volume at constant temperature. How will this change influence the following?(Only write down INCREASES, DECREASES or REMAINSTHESAME.)

6.3.1 Concentration of CCℓ4(g) (1)6.3.1 Value of the equilibrium constant(Kc) (1)

The graph below shows the changes in rate of the reaction after further changes were made to the above equilibrium mixture.

6.4 Write down the disturbance responsible for the sudden change in reaction rate in the 5th minute.

(1)

6.5. Did the temperature INCREASE or DECREASE in the15th minute? (1)6.6. Fully explain the change in the rate of both forward and reverse reactions from

15th until the 22nd minute.(5)

109

[19]

QUESTION 7: WESTERN CAPE Winelands (Sept 2015)

Carbon monoxide gas (CO) and oxygen gas (O2) are placed in a closed container. They are allowed react to form carbon dioxide (CO2).The balanced equation for this reaction is:2CO(g) +O2(g)⇋2CO2(g)The graph below shows concentration changes of reactants and products for this reaction overtime. Use this information to answer the following questions:

7.1 Explain the term chemical equilibrium. (2)7.2 At which times interval(s) is/(are) the reaction at equilibrium? (2)

7.3 Does the FORWARD or the REVERSE reaction have the faster reaction rate during the interval t2 to t3?

(1)

7.4 The temperature is decreased at t4. Is the reaction EXOTHERMIC or ENDOTHERMIC?

(1)

7.5 Explain the answer to QUESTION 7.4 (3)

7.6 What change is made to the reaction at t2? (1)

7.7 How will the change made at t2 influence the value of Kc for this reaction? Write only INCREASE, DECREASE or REMAIN THESAME.

(1)

7.8Initially 63g of CO and 9,11g of O2 is placed in a 2dm3container. At equilibrium the concentration of CO2 is 0,15 mol∙dm-3. Calculate the value of Kc for this reaction.

(10)

[21]

110

UNIT 6: ACIDS AND BASES

QUESTION 1 GAUTENG (Sept 2014)You are given the following ionization reaction of ethanoic acid in water:CH3COOH (aq) ⇌ CH3COO-(aq) + H+(aq) Ka=1,8x10-5

1.1 What does the ionization constant indicate about the strength of the acid? (1)

1.2 What is meant by a concentrated acid? (2)1.3 H2PO4- is an ampholyte.

4

Write an equation to indicate its role as a base. (2)

1.4 Write down a conjugate acid/base pair from your equation in QUESTION 1.3. (1)

1.5 Milk of Magnesia has been used over the ages to relieve stomach ailments caused by excess stomach acid. The active ingredient in Milk of Magnesia is magnesium hydroxide(Mg(OH)2).

A group of learners prepare a solution of magnesium hydroxide.

1.5.1 What mass of Mg(OH)2 must be dissolved in distilled water to prepare

500cm3 of a solution with a concentration of 0,20mol∙dm-3?

(5)

1.5.2 What will the concentration of the hydroxide ions in the solution be?

Assume100%dissociation of magnesium hydroxideinwater. (2)

1.5.3 The pH of any medicine safe for human consumption must lie between pH =4and pH =9. Will this solution that the learners prepare be safe for human consumption? Show all calculations.

(5)

1.6 The learners now check the concentration of their solution that they made. They run a titration using hydrochloric acid of concentration 0,1 mol∙dm-3. They transfer 25cm3 of the magnesium hydroxide solution into a conical flask.The balanced chemical equation for this reaction is:Mg(OH)2(aq) + 2HCℓ (aq) → MgCℓ2(aq) + 2 H20(ℓ)

Determine what volume of HCℓ will be needed to fully neutralize the Milk ofMagnesia if the concentration is actually0,2 mol∙dm-3. (4)

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QUESTION 2: EASTERN CAPE (SEPT 2015)

0,28 g of potassium hydroxide is dissolved in water and titrated against a solution

of sulphuric acid. The end point is reached after adding exactly 20 cm3of a sulphuric acid solution.

The balanced equation for this reaction is:

2KOH(aq) +H2SO4(ℓ)→ K2SO4(aq)+ 2H2O (ℓ)

2.1 Define the term endpoint. (2)

2.2 Calculate the concentration of the sulphuric acid solution. (5)

2.3 AmmoniumnitrateisusedtolowerthepHofagriculturalsoil.Itisproducedby the reaction of ammonia (NH3) with nitric acid (HNO3).

2.3.1 Name the TYPE of reaction that takes place between ammonia and nitric acid.

(1)

2.3.2 Write down a balanced equation for the preparation of ammonium nitrate.

(3)

2.3.3 Is an aqueous solution of ammonium nitrate ACIDIC, ALKALINE orNEUTRAL?

(1)

2.3.4 Explain your answer to QUESTION2.3.3with the aid of a balanced equation.

(4)

[16]

DBE (Feb-Mar 2016)

QUESTION 5

5.1 Define an acid in terms of the Lowry-Brønsted theory. (2)

5.2 Carbonated water is an aqueous solution of carbonic acid, H2CO3. H2CO3(aq) ionises in two steps when it dissolves in water.

5.2.1 Write down the FORMULA of the conjugate base of H2CO3(aq). (1)

5.2.2 Write down a balanced equation for the first step in the ionisation of carbonic acid.

(3)

5.2.3 ThepHofacarbonicacidsolutionat25°C is3,4. Calculate the hydroxide ion concentration in the solution.

(5)

5.3 X is a mono protic acid.

5.3.1 State the meaning of the term monoprotic. (1)112

5.3.2 A sample of acid X is titrated with a standard sodium hydroxide solution using a suitable indicator.

At the endpoint it is found that 25cm3 of acid X is neutralised by

27,5cm3 of the sodium hydroxide solution ofconcentration0,1mol∙dm-3.

Calculate the concentration of acid X. (5)

5.3.3 The concentration of H3O+ ions in the sample of acid X is

2,4x10-4mol∙dm-3.

Is acid X a WEAK or a STRONG acid? (1)

Explain the answer by referring to the answer in Question 5.3.2. (3) [20]IT 7: ELECTROCHEMISTRY

PART 1: Galvanic Cells QUESTION 1: FREE STATE(Sept 2014)

The electrochemical cell represented below is made up of a standard Pb│Pb2+

half-cell and a standard unknown half-cell. The unknown half-cell consists of a metal electrode, X, dipped into a solution of a salt of the metal.

1.1 Which electrode (Pb or X) is the anode? (1)

1.2 Identify electrode X with the aid of a calculation. (5)

1.3 The Pb│Pb2+half-cell is now replaced with a standard Ag│Ag+electrode.

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1.3.1. How will the initial cell potential of this cell compare to that of the above cell? Write down HIGHER THAN LOWER THAN or EQUAL TO. Explain the answer by comparing the relative strengths of the oxidising agents.

(2)

1.3.2 Write down the cell notation for this cell. (3)

[11]

QUESTION 2: EASTERN CAPE (Sept 2015)

2.1 The chloro-alkali industry makes use of brine as electrolyte to produce sodium hydroxide, chlorine and hydrogen gas.

The unbalanced ionic equation for this reaction is:

Cℓ-(aq) + H2O (ℓ) →Cℓ2(g) +H2(g)+ OH-(aq)

2.1.1 Define the term electrolyte. (2)

2.1.2 Write down the FORMULA of the oxidising agent in the above reaction. Use oxidation numbers to explain the answer.

2.1.3 Balance the equation above using half-reactions.

2.2 The following diagram representsagalvaniccellthatfunctionsunder standard conditions.

2.2.1 Which electrode is theanode? (1)

114

2.2.2 Write down the equation for theoxidationhalf-reaction thattakes place.

(2)

2.2.3 Itis found thatthe voltmetergives an initial reading of1,61 V.

Would the voltmeter reading be HIGHER or LOWER if the nickel half- cell is replaced by a copper half-cell under the same conditions? Verify your answer with a calculation.

(5)

[17]

QUESTION 3: GAUTENG (Sept 2014)

The equations A and B below represent two redox reactions.

A: 2Aℓ2O3(s)+ 3C (s)→ 4Aℓ (ℓ) +3CO2(g)

B: Zn(s) + 2Ag+(aq) ⇌Zn2+(aq) +2Ag(s)

3.1 Define oxidation interms of electron transfer. (2)

3.2 Write down the FORMULA of the substance which is:

3.2.1 Reduced in reaction A. (1)

3.2.2 The reducing agent in reaction B. (1)

3.3 A Zn-Ag cell has a cell potential difference of 1,56 V under standard conditions.The cell is allowed to run for 3 hours and the cell potential drops to 1,45V. Using Le Chatelier’s principle, explain the drop in potential difference.

(3)

3.4 For reaction A, write down the half-reaction at cathode. (2)

3.5 What type of energy conversion occurs in a galvanic cell? (1)

[10]

QUESTION 4: EASTERN CAPE (Sept 2014)

4.1 Consider the following half reaction involving oxalic acid solution.2C 02+2H+¿+2e−¿⇌H2 C2O4 ,E°=−0,49V ¿¿

A solution of potassium dichromate (K2Cr2O7(aq)) is added to an oxalic acid(H2C2O4(aq))solution.

4.1.1 Explain why the reaction between the solution of oxalic acid and potassium dichromate will be spontaneous. Refer to the relative strengths of the oxidising and reducing agents in your answer. (3)

115

4.1.2 Use half-reactions to write down a balanced equation for the reaction between oxalic acid and potassium dichromate. Leave theanswer in ionic form without spectator ions. (4)

4.2 A learner sets up astandard electrochemical cell using the following half-cells:

Pt(s)/O2(g)/H+

(aq),H2O2(aq) and Cu2+(aq)/Cu(s)

Potassium chloride (KCℓ(aq)) solution is used in the salt bridge.

4.2.1 Which half cell (A orB) contains the cathode? (2)

4.2.2 Write down the oxidation half-reaction. (2)

4.2.3 Write down the cell notation for this cell. (3)

4.2.4 Calculate the potential difference of the cell (Eᶱcell). (4)4.2.5 After several days, the reading on the voltmeter is 0,00V. Explain

why this reading is obtained.(4)

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116

QUESTION 5: WESTERN CAPE METRO (Sept 2015)

Consider the electrochemical cells below:

In the first electrochemical cell, the Cr/Cr3+ half-cell is connected to a Ag/Ag+ half-cell. Both electrolytes are nitrates under standard conditions. The initial reading on the voltmeter is 1,54V.

5.1 What type of electrochemical cell is this? (1)

5.2 State the standard conditions under which this cell operates. (2)

5.3 Write down the half-reaction that occurs at the anode. (2)5.4 Write down the nett ionic cell reaction (make use of half-reactions.) (2)

5.5 How will the initial reading on the voltmeter change if…5.5.1. A larger Cr plate is used? (1)

5.5.2 The Ag+ solution concentration is doubled? (1)

5.5.3 the Ag/Ag+half-cell is replaced with an Sr/Sr2+half-cell? (1)

Write only INCREASE , DECREASE or NOCHANGE.5.6 The Ag/Ag+ half-cell is now replaced with an unknown electrode X in

its electrolyte. When operating under standard conditions, the initial reading on the voltmeter is 1,08V. After delivering current for a while, it is noticed that the Cr electrode has DECREASED in mass.

5.6.1 Which electrode is the anode :Cr or X? (2)5.6.2 Identify metal X by calculating the standard reduction potential for X.

(5)

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117

PART 2: Electrolytic CellsQUESTION 6: REE STATE (Sept 2014)

The simplified diagram ABOVE represents an electrochemical cell used for the electrolysis of a concentrated sodium chloride solution.

6.1 Is the above cell a GALVANIC or an ELECTROLYTIC cell? (1)6.2 Chlorine gas is released at electrode Q. Write down the:

6.2.1 Electrode (PorQ) at which reduction takes place (1)

6.2.2 Half-reaction that takes place at electrode P (2)

6.2.3 Direction (P to Q or Q to P) in which electrons flowing on the external circuit. (1)

6.2.4 NAME of the species that acts as reducing agent (1)

6.3 Write down the balanced net (overall) cell reaction taking place in this cell. (3)

[9]

QUESTION 7: WESTERN CAPE Winelands (Sept 2015)

7.1 Bauxite ore is dissolved in molten c r y o li t e and purified to Al2O3. From the bauxite, pure molten aluminium is obtained. The cell used for the extraction of aluminium is shown in the sketch below.

118

The net cell reaction for this cell is given as:

2Al2O3+3C →4Al+3CO2

7.1.1 Write down the reduction half reaction for this cell. (2)

7.1.2 Which one of electrode A or electrode B should be connected to thepositive terminal of the power source? (1)

7.1.3 Write down the formula of the oxidising agent in this reaction. (1)

7.2 What is the purpose of using the underlined substance? (2)

7.3 The anodes are regularly replaced during the process. Give a reason for that using an appropriate reaction. (3)

[9]

QUESTION 8: EASTERN CAPE (Sept 2015)

A learner sets up an electrolytic cell, represented in the diagram below, to purify copper which contains platinum and silver impurities.

During the purification of 28 g of the impure copper, 0,8mol of electrons were transferred from the anode to the cathode.

8.1 Calculate the number of copper atoms formed at the cathode. (3)

8.2 The copper used for electrical wiring and cables mustbe 99,99%pure. Determine by calculation whether the IMPURE copper sample is suitable for use in electrical wiring and cables.

(Assume that all the copper at anode has reacted.)

During the purification, a sludge containing the metals platinum and silver form sat the bottom of the container.

119

8.3 Use the relative strengths of reducing agents to explain why platinum and silver atoms are not oxidised during the purification of copper.

(3)

[11]

QUESTION 9: GAUTENG (Sept 2014)

Aluminium oxide is an ionic compound. It is found in the earth’s crust as an ore called bauxite. In order to obtain aluminium; the aluminium oxide is melted and then electricity is passed through it.

9.1 Define the term electrolytic cell. (2)

9.2 Write down the NAMES or FORMULAE of the ions present in the melt. (2)

9.3 Write down the half reaction that occurs at the anode. (2)

9.4 Write down the half reaction that occurs at the cathode. (2)

9.5 Calculate the cell potential for this electrolytic cell if the reaction occurring at the anode has an electrode potential of-0,56V.

(4)

9.6 Explain why the anodes have to be replaced on a regular basis. (1)

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120

QUESTION 10 DBE (Feb-Mar 2011)

Electroplating is one of the uses of electrolysis. The diagram below shows an electrolytic cell that can be used to plate a copper spoon with silver.

10.1

10.2

Define the term oxidation in terms of electron transfer.

What type of half-reaction takes place at the copper spoon? Write down only OXIDATION or REDUCTION

(2)

(1)

10.3

10.4

Write down a half-reaction that explains the change that occurs on the surface of the copper spoon during electrolysis.

Name the metal that is labelled 'electrode'.

(2)

(1)

10.5 Give a reason why the concentration of the AgNO3(aq) remains constant during electrolysis.

(2)

10.6 Write down the half reaction that occurs at the cathode. (2)

10.7 Calculate the cell potential for this electrolytic cell if the reaction occurring at the anode has an electrode potential of -0,56V.

(4)

10.8 Explain why the anodes have to be replaced on a regular basis. (1)

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121

CHEMICAL SYSTEMS

UNIT 8 - FERTILIZERS

QUESTION 1

1.1. A gardener needs a fertiliser with the highest percentage of the relevant nutrient to obtain a green lawn

Which ONE of the following NPK fertilisers will give the best results?A 8 : 1 : 5

B 7 : 1 : 1

C 3 : 2 : 3

D 3 : 1 : 5 (2)

1.2. Eutrophication involves the following stages:

(i) Increase in growth of algae (ii) Increase in nitrate concentration (iii) Death of fish (iv) Decrease in oxygen concentration

Which ONE of the following CORRECTLY represents the order in which these stages occur?

A (i) (ii) (iii) (iv)

B (i) (ii) (iv) (iii)

C (ii) (i) (iii) (iv)

D (ii) (i) (iv) (iii) (2)

1.3. Which ONE of the following is a primary nutrient for plants?

A. Oxygen B. Carbon C. Potassium D. Magnesium (2)

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QUESTION 2 (DBE MARCH 2013)

Different processes used in the preparation of fertilizers C and F are represented in the flow diagram below. 2.1 Write down the NAME or FORMULA of:

2.1.1 Gas A (1)

2.1.2 Gas B (1)

2.1.3 Fertiliser F (1)

2.2 Sulphuric acid is used to prepare fertilizer C.

Write down:

2.2.1 The name of the industrial process used to prepare sulphuric acid (1)

2.2.2 A balanced equation for the preparation of fertilizer C (3)

2.3 Gases D and E are prepared during the Ostwald process.

Write down the: 2.3.1 Name given to the preparation of gas D from ammonia (1) 2.3.2 Balanced equation for the preparation of gas D (3) 2.3.3 NAME or FORMULA of gas E (1)

[12]123

QUESTION 3 (DBE NOV2014)

3.1 The flow diagram below shows the processes involved in the industrial preparation of fertilizer Q.

Write down the:

3.1.1 NAMES or FORMULAE of the reactants used in the Haber process (2)

3.1.2 Balanced equation for the formation of fertilizer Q (3)

3.2 The diagram below shows a bag of NPK fertiliser.

Calculate the mass of nitrogen in the bag. (4) [9]

124

kg20

)6(35–1–3

QUESTION 4 (DBE NOV 2010)

Ammonia, ammonium nitrate and ammonium sulphate are three important

Nitrogen-containing fertilizers: the flow diagram below shows how these fertilizers are produced in industry.

4.1 Use the information in the flow diagram above and write down the following:

4.1.1 Name of Process 1 (1)

4.1.2 Balanced equation for Process 2 (3)

4.1.3 NAME or FORMULA of compound X (1)

4.1.4 Balanced equation for the preparation of ammonium sulphate using sulphuric acid and compound Y (3)

4.1.5 NAME or SYMBOL of the primary nutrient in ammonium sulphate (1)

4.2 Write down ONE positive impact of fertilisers on humans. (2)

4.3 Write down TWO negative impacts of the use of ammonium nitrate, as fertiliser, on humans. (4)

125

4SO2H

Nitrogen

Natural gasAir

Process 1

Hydrogen

Process 2

Compound X

Compound Y

processOstwald

Sulphur

3SO

NitrateAmmonium

sulphateAmmonium

Contact process

The reaction below represents the catalysed step in the contact process: 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH < 0

4.4 The reaction takes place in a closed container and reaches equilibrium at 427 °C. How will a HIGHER temperature affect each of the following? Write down only INCREASES, DECREASES or REMAINS THE SAME.

4.4.1 The rate of production of SO3(g) (2)

4.4.2 The yield of SO3(g) (2)

4.5 The reaction is investigated on a small scale in the laboratory. Initially 4 mol of SO2(g) and an unknown mass, x, of O2(g) are sealed in a 2 dm3 flask and allowed to reach equilibrium at a certain temperature. At equilibrium it is found that the concentration of SO3(g) present in the flask is 1,5 mol∙dm-3.

Calculate the mass of O2(g) initially present in the flask if the equilibrium constant (Kc) at this temperature is 4,5

[2]

126

QUESTION 5 (DBE MARCH 2015)

Reactions A, B, C and D in the flow diagram below represent the manufacturing of Fertilizer X.

5.1 Write down the name of the industrial preparation of sulphuric acid. (1)

5.2. Write down the:

5.2.1 NAME or FORMULA of the catalyst used in reaction A (1)

5.2.2 Balanced equation for reaction C (3)

5.3 Ammonia is one of the reactants used in reaction D to make Fertiliser X.

Write down:

5.3.1 A balanced equation for reaction D (3)

5.3.2 The NAME of Fertiliser X (1)

5.4 Two 50 kg bags, containing fertilizers P and Q respectively, are labelled as follows:

Fertiliser P: 5 : 2 : 3 (25) Fertiliser Q: 1 : 3 : 4 (20)

5.4.1 What do the numbers (25) and (20) on the labels represent? (1)

5.4.2 Using calculations, determine which fertiliser (P or Q) contains the greater mass of potassium. (4)

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127

QUESTION 6 (DBE MARCH 2011)

Fertilisers allow farmers to grow crops in the same soil year after year. However, environmental problems, such as eutrophication, are associated with the application of fertilisers.

6.1 State ONE PRECAUTION that a maize farmer can take to prevent eutrophication. (1)

Nitric acid is an important reactant in the production of ammonium nitrate, a nitrogen-based fertiliser.

6.2 Write down the name of the industrial process for the production of nitric acid. (1)

6.3 Write down a balanced equation for the preparation of ammonium nitrate from nitric acid. (3)A fertiliser company produces ammonia on a large scale at a temperature of 450 °C. The balanced equation below represents the reaction that takes place in a sealed container.

N2(g) + 3H2(g) ⇌ 2NH3(g) ∆H < 0To meet an increased demand for fertiliser, the management of the company instructs their engineer to make the necessary adjustments to increase the yield of ammonia.In a trial run on a small scale in the laboratory, the engineer makes adjustments to the TEMPERATURE, PRESSURE and CONCENTRATION of the equilibrium mixture. The graphs below represent the results obtained.

128

6.4 Identify the changes made to the equilibrium mixture at each of the following times:6.4.1. t1 (2)

6.4.2. t2 (2)

6.4.3. t3 (2)

6.5. At which of the above time(s) did the change made to the reaction mixture lead to a higher yield of ammonia? Write down only t1 and/or t2 and/or t3. (2)

6.6. The engineer now injects 5 mol N2 and 5 mol H2 into a 5 dm3 sealed empty container. Equilibrium is reached at 450 °C. Upon analysis of the equilibrium mixture, he finds that the mass of NH3 is 20,4 g. (9)

[22]

129

Time (minutes)

Concentration (mol∙dm-

3) 0 t1 t2 t3

QUESTION 07 – (DBE 2016)

Ammonium nitrate is an important fertilizer. It is produced by reacting nitric acid with ammonia. Both nitric acid and ammonia are prepared on a large scale in industry.

7.1 Write down the name of the industrial preparation of nitric acid. (1)

7.2 The catalytic oxidation of ammonia is one of the steps in the process named in QUESTION 7.1.

Write down the NAMES or FORMULAE of the TWO products formed in this step. (2)

7.3 Write down a balanced equation for the preparation of ammonium nitrate. (3)

7.4 Calculate the mass, in kilogram, of ammonium nitrate that can be made from 6,8 x 104 kg of ammonia and excess nitric acid.

(One mole of ammonia produces one mole of ammonium nitrate.) (3)

7.5 Ammonium nitrate is often mixed with potassium chloride and ammonium phosphate. Give a reason why it is mixed with these compounds. (1)

[10]

130

QUESTION 08 (DBE FEB 2010)

A learner who is revising for a test on fertilisers, summarises her notes as follows:

8.1 Write down the NAME of the industrial process in Step I used to extract nitrogen gas from the atmosphere. (1)

8.2 The Haber process, indicated in Step II, is represented by the following equation:

3H2(g) + N2⇌ 2NH3(g) ∆H < 0

In this process, high temperatures of approximately 450 °C are used. Explain in terms of reaction rate, equilibrium and temperature why such a high

temperature, and not a lower temperature, is used. (4)

8.3 Write a balanced chemical equation for the reaction that produces the Nitrogen fertiliser in Step IV. (3)

8.4 The learner decides to educate the community about the possible negative effects of the overuse of nitrogen fertilisers on the environment. Write down the main arguments that she will raise to convince the community to avoid excessive use of nitrogen fertilisers. (4)

8.5 The learner notes that fertiliser with an NPK ratio of 7:1:1 is needed for the growth of maize plants.

8.5.1 State what the term NPK ratio means. (2)

8.5.2 Will the fertiliser with this NPK ratio lead to a good crop yield? Explain the answer. (3)

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131

3NH

Step IV

IIIStep

Step II

IStep

NITRIC ACID (OSTWALD PROCESS)

(Industrial)2NSASOL) (production2H

NITROGEN FERTILISER