1 SECONDARY SCHOOL IMPROVEMENT PROGRAMME
(SSIP) 2014
GRADE 12
SUBJECT:
PHYSICAL SCIENCE
LEARNER EXTRA SESSIONS
(Page 1 of 50)
© Gauteng Department of Education
2 TABLE OF CONTENTS
SESSION NO
TOPIC
EXAM TIPS
3
1
CIRCUIT DIAGRAMS
4 - 14
2
MOMENTUM AND PROJECTILE MOTION
14 - 24
3
ACIDS AND BASES / ELECTROCHEMISTRY
25 - 32
4
ORGANIC CHEMISTRY
32 - 41
5
REACTION RATES AND CHEMICAL
EQUILIBRIUM
42 - 50
PAGE
© Gauteng Department of Education
3 PHYSICAL SCIENCE EXAM TIPS
Ø
USE THE PHYSICAL SCIENCE EXAMINATION GUIDELINE 2014 AS A CHECKLIST
Ø
READ THE INSTRUCTIONS BEFORE YOU START ANSWERING THE QUESTIONS
Ø
Use your 10 minute reading time effectively – you will receive the question paper at
least 10 minutes before the start time
Ø
Do not spend more than 20 minutes on Section A – if you do not know the answer to a
one word question leave it out – sometimes in the body of the long questions , the
examiners may inadvertently refer to it and then you can go back and insert it. Also, use
the information sheet with its formulae to help with answering the questions from
Section A. Never leave a multiple choice question unanswered – if you do not know the
answer even after trying the process of elimination – then take a guess.
Ø
If you learn your scientific definitions well, this will help you with answering Section A
as well.
Ø
Answer the questions first that you feel you know the content the best. Just number your
questions clearly and start a new question on a new page.
Ø
Use your data sheets – they are there to help you. Make a list of all the physical
quantities given, and then try and identify the equation that needs to be used in
answering the question. Sometimes two calculations may be required to answer a
question.
Ø
WITH PHYSICS ALWAYS THINK WITH YOUR PENCIL!!! Make a sketch of the situation
– many times when we visualize a problem, it becomes clearer as to what needs to be
done to arrive at the answer.
Ø
REMEMBER YOUR UNITS AND DIRECTION!!!!
Ø
If you are required to draw a graph, label the axes correctly with the physical quantity
and its corresponding units and give your graph a heading. Remember, the
independent variable goes on the x-axis and the dependent variable on the y-axis.
Ø
Watch your time – remember to use the rule “a mark a minute” so that you will have
time to go back to check your work and to complete a question that you have left out!!
Ø
PREPARATION IS THE KEY TO SUCCESS!!! Make sure that you have given
yourself every opportunity of reaching your potential and of achieving the marks
you feel you deserve. Practice, practice, practice. You need to learn the theory
but you need to apply it as well.
Ø
Try to understand what a formula says and means, and what each symbol represents
and its units. If you understand the physical concepts underlying the formulae, deriving
them or remembering them and using them are easy.
Ø
When doing a calculation, always write down the formula as given on the
information sheet. Substitute the values into the formula and then manipulate the
equation and answer the question. Remember your unit and direction.
Ø
BE WELL PREPARED, REMEMBER YOUR STATIONERY AND CALCULATOR AND
LEAVE HOME EARLY IN ORDER TO GET TO SCHOOL ON TIME!!!
Ø
GOOD LUCK!!
© Gauteng Department of Education
4 EXTRA SESSION NO: 1
TOPIC: CIRCUIT DIAGRAMS
Please ensure that you know the following as per the Physical Science Examination
Guidelines 2014:
Ohm's law
• State Ohm's law in words: The potential difference across a conductor is directly
proportional to the current in the conductor at constant temperature.
• Determine the relationship between current, potential difference and resistance at constant
temperature using a simple circuit.
• State the difference between ohmic conductors and non-ohmic conductors and give an
example of each.
• Solve problems using V = IR for series and parallel circuits (maximum four resistors).
Power, energy
• Define power as the rate at which work is done.
• Solve problems using W = p∆t
• Solve problems using P = VI ,P = I2R
• Solve circuit problems involving the concepts of power and electrical energy.
• Deduce that the kilowatt hour (kWh) refers to the use of 1 kilowatt of electricity for
1 hour.
• Calculate the cost of electricity usage given the power specifications of the appliances
used, the duration and the cost of 1 kWh.
Internal resistance, series and parallel networks
• Solve problems involving current, voltage and resistance for circuits containing
arrangements of resistors in series and in parallel (maximum four resistors).
• Explain the term internal resistance.
• Solve circuit problems using ε = Vload + Vinternal resistance or ε =IRext+ Ir.
• Solve circuit problems, with internal resistance, involving series-parallel networks of
resistors (maximum four resistors).
TYPICAL EXAM QUESTIONS
MULTIPLE CHOICE QUESTIONS: 20 minutes (ADAPTED FROM FINAL DoE QUESTION
PAPERS)
1. The circuit represented below is used to investigate the relationship between the
current passing through and the potential difference across resistor P.
© Gauteng Department of Education
5 S A P V The results obtained are used to draw the graph below.
Current (A) Graph of current versus potential difference
0 , 8 0 , 6 0 4 , 0 , 2 1 0 0 , 5 1 , 5 2 2 5 , Potential difference (V)
1.1
1.2
Write down the independent variable.
A. current
B. potential difference
C. resistance
D. temperature
Write down the variable that must be controlled.
A. current
B. potential difference
C. resistance
D. temperature
1.3 Write down the conclusion that can be obtained from the graph.
A. The potential difference across the ends of a resistor is directly proportional to the
current through it, provided the temperature remains constant.
B. The potential difference across the ends of a resistor is inversely proportional to the
current through it, provided the temperature remains constant.
C. The resistance of a conductor is directly proportional to the current through it,
provided the temperature remains constant.
© Gauteng Department of Education
6 D. The resistance in a conductor is inversely proportional to the potential difference
across the conductor, provided the temperature remains constant.
1.4 Using the gradient of the graph, calculate the resistance of resistor P.
A. 1,24 Ω
B. 2,25 Ω
C. 2,78 Ω
D. 3,35 Ω
2.
In the circuit represented below, a battery of emf 30 V and unknown internal resistance r
are connected to resistors, as shown. Ignore the resistance of the ammeter and the
connecting wires.
r 8 Ω A 5 Ω V 6 Ω 10 Ω The current passing through the 10 Ω resistor is 0,6 A.
Calculate the:
2.1
Equivalent resistance of the two resistors in parallel.
A. 2,45 Ω
B. 2,89 Ω
C. 3,25 Ω
D. 3,75 Ω
2.2
Current through the 8 Ω resistor.
A. 1,6 A
B. 2,4 A
C. 3,2 A
D. 4,5 A
Internal resistance of the battery.
A. 1,5 Ω
B. 1,25 Ω
C. 2 Ω
D. 3,2 A
2.3
3.
In the circuit diagram below, the battery has an emf of 12 V and an internal
resistance of 0,8 Ω. The resistance of the ammeter and connecting wires may
be ignored.
© Gauteng Department of Education
7 12 V 0 ,8 Ω 2 Ω A 4 Ω 8 Ω 8 Ω V Calculate the:
3.1
3.2
3.3
Effective resistance of the circuit
A. 2,5 Ω
B. 4 Ω
C. 6 Ω
D. 7 Ω
Reading on the ammeter
A. 2 A
B. 3 A
C. 4,5 A
D. 5,2 A
Reading on the voltmeter
A. 0,8 V
B. 3,2 V
C. 4,5 V
D. 5.5 V
(10 X 2) = [20]
LONG QUESTIONS
QUESTION 1: 15 minutes (Taken from the DoE Feb–March 2010)
The circuit diagram below shows a battery, with an internal resistance r, connected to three
resistors, M, N to Y. The resistance of N is 2Ω and the reading on voltmeter V is 14V. The
reading on ammeter A1 is 2A and the reading on ammeter A2 is 1A. (The resistance of the
ammeters and the connecting wires may be ignored.)
© Gauteng Department of Education
8 1.1.
1.2.
State Ohm’s law in words.
(2)
How does the resistance of M compare with that of N? Explain how you arrived at
the answer.
(2)
1.3.
If the emf of the battery is 17V, calculate the internal resistance of the battery.
(5)
1.4.
Calculate the potential difference across resistor N.
(3)
1.5.
Calculate the resistance of Y.
(4)
[16]
QUESTION 2: 15 Minutes (Taken from the DOE Physical Sciences Exemplar 2008)
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.
2.1
2.1.1
2.2.2
2.2.3
Planning
What is the investigative question for this investigation?
(2)
Write down a possible hypothesis for this investigation.
(2)
Write down ONE variable that the learners must control during this investigation. (1)
2.2
2.2.1
2.2.2
2.2.3
Design
List ALL the apparatus that the learners will need for this investigation.
Draw a circuit diagram that they can use to assemble the apparatus.
Describe, in not more than four lines, how the learners must use this apparatus
to take the required measurements.
© Gauteng Department of Education
(3)
(3)
(3)
[14]
9 QUESTION 3: 15 Minutes
(PRACTICE QUESTIONS - Questions taken from various DBE Exemplars and Final
Examinations)
The headlights of a car are connected in parallel to a 12 V battery, as shown in the
simplified circuit diagram below. The internal resistance of the battery is 0,1 Ω and
each headlight has a resistance of 1,4 Ω. The starter motor is connected in parallel with
the headlights and controlled by the ignition switch, S2. The resistance of the
connecting wires may be ignored.
emf = 12 V
0,1 Ω
1,4 Ω
1,4 Ω
  S1
  S2
3.1
3.2
3.3
State Ohm's law in words.
With only switch S1 closed, calculate the following:
3.2.1 Effective resistance of the two headlights
3.2.2 Potential difference across the two headlights
3.2.3 Power dissipated by one of the headlights
(3)
(4)
(3)
Ignition switch S2 is now closed (whilst S1 is also closed) for a short time and
the starter motor, with VERY LOW RESISTANCE, rotates. How will the
brightness of the headlights be affected while switch S2 is closed? Write
down only INCREASES, DECREASES or REMAINS THE SAME.
Explain how you arrived at the answer.
(4)
[16]
(2)
© Gauteng Department of Education
10 QUESTION 4: 16 Minutes (Taken from SUNDAY TIMES EXEMPLAR)
Arnold and Mary construct a circuit as shown in the circuit diagram below. The circuit contains
a fresh, fully charged, 24 V battery with an internal resistance of 1 Ω.
24 V; 1 Ω S V2 A1 3 Ω
V1 R A 2 12 Ω When the switch S is closed, Mary reads the ammeter A1 and records a current of 3 A.
4.1 Using this value of the reading on A1, i.e. 3A, calculate the
4.1.1 Value of the unknown resistance R
4.1.2 The reading on the voltmeter V1
4.1.3 The reading on the voltmeter V2
4.1.4 The reading on the ammeter A2
4.1.5 The energy dissipated per second in the battery when charge is flowing in the
circuit.
4.2
(3)
The switch S remains closed and charge is allowed to flow in the circuit for a long time.
State whether the following readings will INCREASE, DECREASE or REMAIN
UNCHANGED:
4.2.1 A1
(1)
4.2.2 A2
(1)
4.2.3 V1
(1)
4.2.4 V2
(1)
[20]
(4)
(3)
(3)
(3)
© Gauteng Department of Education
11 QUESTION 5: 12 Minutes (Taken from DoE 2009 Prelim)
The following circuit shows a battery consisting of four 1.5 V cells connected in series. An
ammeter with negligible resistance is connected in series to the battery. The reading on the
ammeter is 0.5 A when the switch is closed. The connectors have negligible resistance and
the voltmeters have very high resistance. Voltmeter V1 has a reading of 5.5 V when the
switch is closed.
V
5Ω
A
6Ω
4Ω
15 Ω
V
Calculate the value of the internal resistance of a single cell.
Calculate the value of the resistance of the external circuit.
Calculate the value of the reading on voltmeter V2
5.1.1
5.1.2
5.1.3
(4)
(4)
(4)
[12]
QUESTION 6: 12 Minutes (Taken from DoE – UNUSED NOVEMBER 2009)
When both switches are open, the voltmeter across the battery reads 9 V.
Three resistors, R1, R2 and R3, are connected to a battery, as shown in the circuit
diagram below. The internal resistance of the battery is 0,3 Ω. The resistance of R2 and
R3 is equal. The resistance of R1 is half that of R2.
© Gauteng Department of Education
12 9 V S 1 r 0 ,3 Ω V 1 R 1 = R N S 2 R 2 = 2R R 3 = 2R A 6.1 What is the value of the emf of the battery? Give a reason a reason for your answer. (2)
6.2 When only switch S1 is closed, the reading on the ammeter is 3 A. Calculate the
resistance of R1.
(5)
6.3 Both the switches are now closed.
6.3.1 How will the resistance of the circuit change? Write down only INCREASE,
DECREASE or REMAINS THE SAME
(1)
6.3.2 A conducting wire of negligible resistance is connected between points Q and N.
What effect will this have on the “lost volts”? Explain your answer.
(3)
[11]
QUESTION 7: 10 Minutes (Taken from DoE ADDITIONAL EXEMPLAR 2008)
© Gauteng Department of Education
13 Four resistors of different resistances are connected in a circuit. The battery has an emf of 30
V and an internal resistance of 2 Ω. The resistance of the connecting wires is negligible.
7.1 Define the concept emf of a battery.
(2)
7.2 Calculate the potential difference between points X and Y.
(7)
[9]
QUESTION 8: 15 MIN (TAKEN FROM DoE FEB/MARCH 2011)
The circuit diagram below represents a combination of resistors in series and parallel.
The battery has an emf of 12 V and an unknown internal resistance r. A is 1.2A.
= 12
V
r
A
P• S
• • 8
6
8.1
8.2
8.3
8.4
• Q
3,6
Calculate the total resistance of the circuit.
Calculate the internal resistance of the battery.
Calculate the energy dissipated in the 6 Ω resistor in 3 minutes.
Switch S is now CLOSED.
8.4.1
What is the total resistance of the circuit?
8.4.2
What is the reading on ammeter A
8.5
A conducting wire of negligible resistance is now connected between points P
and Q. What effect will this have on the temperature of the battery?
© Gauteng Department of Education
(3)
(4)
(3)
(1)
(1)
14 Write down only INCREASES, DECREASES or REMAINS THE SAME.
Explain how you arrived at the answer.
(4)
[16]
EXTRA SESSION NO: 2
TOPIC: MOMENTUM AND PROJECTILE MOTION
Please ensure that you know the following as per the Physical Science Examination
Guidelines 2014:
Momentum
•
Define momentum as the product of an object's mass and its velocity.
•
Describe the linear momentum of an object as a vector quantity with the same direction
as the velocity of the object.
•
Calculate the momentum of a moving object using p = mv.
•
Describe the vector nature of momentum and illustrate it with some simple examples.
•
Draw vector diagrams to illustrate the relationship between the initial momentum, the
final momentum and the change in momentum for each of the above examples.
Newton's second law of motion in terms of momentum
State Newton's second law of motion in terms of momentum: The resultant/net force
acting on an object is equal to the rate of change of momentum of the object in the
direction of the resultant/net force.
•
Express Newton's second law of motion in symbols: Fnet= ∆p ∆t .
•
Calculate the change in momentum when a resultant/net force acts on an object and its
velocity:
o
Increases in the direction of motion, e.g. 2nd stage rocket engine fires
o
Decreases, e.g. brakes are applied
o
Reverses its direction of motion, e.g. a soccer ball kicked back in the
direction it came from
•
Impulse
•
Define impulse as the product of the resultant/net force acting on an object and the
time the resultant/net force acts on the object.
•
Deduce the impulse-momentum theorem: FnetΔt = mΔv.
•
Use the impulse-momentum theorem to calculate the force exerted, the time for which
the force is applied and the change in momentum for a variety of situations involving
the motion of an object in one dimension.
•
Explain how the concept of impulse applies to safety considerations in everyday life,
e.g. airbags, seatbelts and arrestor beds.
Conservation of momentum and elastic and inelastic collisions
•
Explain what is meant by a closed / an isolated system (in Physics), i.e. a system on
which the resultant/net external force is zero.
•
A closed / an isolated system excludes external forces that originate outside the
colliding bodies, e.g. friction. Only internal forces, e.g. contact forces between the
colliding objects, are considered.
© Gauteng Department of Education
•
15 State the principle of conservation of linear momentum: The total linear momentum of
a closed system remains constant (is conserved).
You must be able to:
Ø Explain what is meant by a projectile, i.e.: an object upon which the only force acting is the
force of gravity.
Ø Use equations of motion to determine the position, velocity and displacement of a
projectile at any given time.
Ø Sketch position versus time (x vs. t), velocity versus time (v vs. t) and acceleration versus
time (a vs. t) graphs for:
•
A free-falling object
•
An object thrown vertically upwards
•
An object thrown vertically downwards
•
Bouncing objects (restricted to balls)
For a given x vs. t, v vs. t or a vs. t graph, determine:
• Position
• Displacement
• Velocity or acceleration at any time t
For a given x vs. t, v vs. t or a vs. t graph, describe the motion of the object:
• Bouncing
• Thrown vertically upwards
• Thrown vertically downward
Ø Apply the conservation of momentum to the collision of two objects moving in one
dimension (along a straight line) with the aid of an appropriate sign convention.
Ø Distinguish between elastic collisions and inelastic collisions by calculation.
Ø Explain what is meant by a projectile, i.e. an object upon which the only force acting is the
force of gravity.
TYPICAL EXAM QUESTIONS
QUESTION 1: 15 Minutes (Taken from DoE 2008 ADDITIONAL EXEMPLAR)
New cars have a crumple zone to help minimise injuries during accidents. In addition seat
belts, air bags and padded interiors can reduce the chance of death or serious injury.
1.1 Use principles in Physics to explain how air bags can reduce the chance of death or
injury.
(3)
1.2 In a crash test, a car of mass 1,2 x 103 kg collides with a wall and rebounds as
illustrated below. The initial and final velocities of the car are 12 m·s-1 to the left and 2
m·s-1 to the right respectively. The collision lasts 0,1 s.
© Gauteng Department of Education
16 -­‐1
12 m·s -­‐ 1
2 m·s Calculate the:
1.2.1 Impulse of the car during the accident
1.2.2 Average force exerted on the car
(4)
(3)
1.3 How will the magnitude of the force exerted on the car be affected if the time interval of
the collision remains 0,1 s, but the car does not bounce off the wall? Write down only
INCREASES, DECREASES or REMAINS THE SAME. Explain your answer. (2)
[12]
QUESTION 2: 15 Minutes (Taken from DoE 2008 EXEMPLAR)
Collisions happen on the roads in our country daily. In one of these collisions, a car
of mass 1 600 kg, travelling at a speed of 30 m·s-1 to the left, collides head-on with a
minibus of mass 3 000 kg, travelling at 20 m·s-1 to the right. The two vehicles move
together as a unit in a straight line after the collision.
3 000 1 600 20 m
·s-­‐1 2.1
2.2
2.3
30 m
·s-­‐1 Calculate the velocity of the two vehicles after the collision.
Do the necessary calculations to show that the collision was inelastic.
The billboard below advertises a car from a certain manufacturer.
Safety Both in one first! package! Airbag Crumple zone Before After impact impact © Gauteng Department of Education
(6)
(6)
17 Use your knowledge of momentum and impulse to justify how the safety features mentioned
in the advertisement contribute to the safety of passengers.
(3)
[15]
QUESTION 3: 10 Minutes (Taken from DoE NOVEMBER 2008)
The most common reasons for rear-end collisions are too short a following distance,
speeding and failing brakes. The sketch below represents one such collision.
Car A of mass 1 000 kg, stationary at a traffic light, is hit from behind by Car B of mass
1 200 kg, travelling at 18 m·s-1. Immediately after the collision Car A moves forward at 12
m·s-1.
Before A fte r Car A -­‐ 1 12 m·s Car A ? -­‐1 18 m·s Car B Car B 3.1
Assume that linear momentum is conserved during this collision. Calculate the
speed of Car B immediately after the collision.
(4)
3.2 Modern cars are designed to crumple partially on impact. Explain why the assumption
made in QUESTION 3.1 may NOT be valid in this case.
(2)
3.3
A traffic officer appears at the scene of the accident and mentions the dangers of a
head-on collision. He mentions that for cars involved in a head- on collision, the risk of
injury for passengers in a heavier car would be less than for passengers in a lighter car.
Use principles of Physics to explain why the statement made by the traffic
officer is correct.
(3)
[9]
QUESTION 4: 15 Minutes (TAKEN FROM DoE NOVEMBER FINAL – 2009)
A man of mass 87 kg on roller skates, moving horizontally at constant speed in a straight line,
sees a boy of mass 22 kg standing directly in his path. The man grabs the boy and they both
continue in a straight line at 2,4m·s-1.
4.1
4.2
Calculate the man's speed just before he grabs the boy. Ignore the effects of friction.
(4)
Is the collision elastic? Use a calculation to support your answer.
(6)
After grabbing the boy, they both continue at a velocity of 2,4 m·s-1 along a
straight line, until they arrive at a loose gravel surface near the end of the path.
They now move at constant acceleration in a straight line through the loose
gravel for 2 m before coming to rest.
4.3
© Gauteng Department of Education
18 Calculate the magnitude of the force exerted by the gravel surface on the
man and the boy.
(5)
[15]
QUESTION 5: 10 Minutes (Taken from DoE NOVEMBER 2009)
Tarzan, of mass 80 kg, swings from rest on a rope of length 10 m that is horizontal
when he starts, as shown in the diagram below. At the bottom of his swing, he picks
up Jane, sitting on the ground, in an inelastic collision. Jane has a mass of 50 kg.
They then swing upwards as one unit.
The mass of the rope and the effects of air friction may be ignored.
Tarzan – 80 kg  10 m 5.1
5.2
90 ° Jane – 50 kg State the principle of conservation of linear momentum in words.
Calculate the combined speed of Tarzan and Jane just after he picks her up.
QUESTION 6:
20 Minutes (Taken from DoE PRE-LIM 2009)
Two boys Franck and Mandla have masses of 50 kg and 80 kg respectively. They stand
on a stationary trolley of mass 180 kg. The trolley is free to move in a horizontal plane
either to the left or to the right. The boys simultaneously jump off the trolley in opposite
directions from each end of the trolley. Both the boys leave the trolley with an initial
speed of 3 m·s-1 relative to the ground.
© Gauteng Department of Education
(2)
(8)
[10]
19 Franck Mass: 50 kg Speed before jump: 0 m·s-­‐1 Speed after jump: 3 m ·s-­‐1 Trolley 6.1
6.2
6.3
6.4
6.5
Mandla Mass: 80 kg Speed before jump: 0 m·s-­‐1 Speed after jump: 3 m ·s-­‐1 Mass: 180 kg Calculate the magnitude and direction of the velocity at which the trolley
starts to move immediately after the boys have jumped off the trolley.
Give a reason why the velocity of the trolley calculated in 5.1 does not
remain constant after the boys have jumped off.
Explain, using Newton’s second Law, why the trolley moves in the
direction as calculated in question 6.1 as above.
The time it takes for Mandla to push against the trolley with his legs is
0.2 s. During this time the trolley exerts a force on Mandla. Calculate the
magnitude of the force the trolley exerts on Mandla during the time it
takes for Mandla to push against the trolley.
Explain why Mandla accelerates towards the right if the force exerted on
Mandla by the trolley and the force Mandla exerts on the trolley has the
same magnitude but act in opposite directions to each other.
(6)
(2)
(4)
(3)
(2)
[17]
QUESTION 7: 20 Minutes (Taken from various DoE Exemplars to develop
practice papers)
The roof of a tall building is 25 m above the ground. A rigid ball of mass 0,3 kg falls freely
when dropped from the roof. It strikes the concrete floor on the ground with velocity v .
It bounces to a maximum vertical height of 6m.
The ball was in contact with the floor for 0,9 s. Ignore the effects of friction.
© Gauteng Department of Education
1
20 7.1
7.2
7.3
7.4
Calculate the velocity, v1 , when the ball first hits the floor.
Calculate the impulse of the ball as a result of the collision.
Calculate the magnitude of the net force exerted on the ball.
Using the ground as zero reference, draw a sketch graph of position
(displacement) versus time for the motion of the ball from its original height
until it reaches its second maximum height.
Indicate the relevant position values on the y-axis.
7.5 The rigid ball is now replaced with a softer ball of the same mass and volume
as the rigid ball. It is then dropped from the same height onto the concrete
(3)
(7)
(3)
(4)
floor. Will the ball reach the SAME, GREATER or LESSER height compared
to the previous ball? Use principles of physics to explain your answer.
(3)
[20]
QUESTION 8: 15 Minutes (TAKEN FROM THE SUNDAY TIMES EXEMPLARS)
A 400 g ball is thrown vertically into the air with a velocity of 28,69 m·s-1. The ball takes 5,84 s
to return to the ground. On striking the ground, the ball bounces and reaches a height that is
exactly half the maximum height attained in the throw.
8.1
8.2
8.3
8.4
Calculate the maximum height attained by the ball when thrown upwards.
Determine the velocity of the ball the instant before it strikes the ground.
Calculate the velocity of the ball the instant after bouncing off the ground.
If the average force exerted by the ground on the ball as it bounces is 103 N, for
how long are the ball and ground in contact? You may ignore the effects of friction.
(3)
(2)
(4)
(6)
[15]
© Gauteng Department of Education
21 QUESTION 9: 15 Minutes (TAKEN FROM DoE ADDITIONAL EXEMPLAR 2008)
Any falling object which is being acted upon only by the force of gravity is said to be in a
state of free fall.
9.1 Briefly describe how you can make use of a small free-falling stone to determine how
deep the water level is in a well (represented by y in the diagram below).
(3)
y WATER 9.2 Give ONE reason why the concept of free fall might not give a correct
answer.
(1)
9.3 A student is at the top of a building of height h. He throws a stone X upward
with a speed v. He then throws a second identical stone Y downward at the
same speed v.
Position (m) 9.3.1 Redraw the following set of axes in the ANSWER BOOK and sketch the graphs
of position versus time for each of the stones X and Y. Use the ground as the
point of zero position.
(4)
t(s)
9.3.2 How will the velocities of the two stones X and Y, compare when they reach the
ground? Explain your answer.
(4)
[9]
© Gauteng Department of Education
22 QUESTION 10: 10 Minutes (Taken from DoE EXEMPLAR 2008)
A hot-air balloon is rising vertically at constant velocity. When the balloon is at a
height of 88 m above the ground, a stone is released from it. The displacement-time
graph below represents the motion of the stone from the moment it is released from
the balloon until it strikes the ground. Ignore the effect of air resistance.
 100   Displacement (m) 80  60 40 20 0 10.1
10.2
1 2 3 4 5 6 Time (s)  Use information from the graph to answer the following questions:
Calculate the velocity of the hot-air balloon at the instant the stone is
released.
Draw a sketch graph of velocity versus time for the motion of the stone from
the moment it is released from the balloon until it strikes the ground.
Indicate the respective values of the intercepts on your velocity-time graph.
(6)
(3)
[9]
QUESTION 11: 15 Minutes (Taken from DoE NOVEMBER 2009)
A ball is released from a certain height. The velocity-time graph below represents the motion
of the ball as it bounces vertically on a concrete floor. The interaction time of the ball with the
floor is negligibly small and is thus ignored.
© Gauteng Department of Education
23 Graph of velocity versus time
v 4 ( m·s -­‐1) 2 0 -­‐2 -­‐4 11.1
11.2
11.3
0 ,2 0 ,4 0 ,6 0 ,8 1 ,0 1 ,2 1 ,4 t (s) Describe the changes, if any, in velocity and acceleration of the ball from
t = 0 s to t = 0,4 s.
(4)
Without using the equations of motion, calculate the height from which the ball has
been dropped initially.
(4)
Copy the set of axes below into your ANSWER BOOK.
y
(m)
0 ,2 0 ,4 0 ,6 0 ,7 t (s ) Use the given velocity versus time graph for the motion of the ball to sketch the
corresponding position-time graph for the time interval 0 s to 0,7 s.
(3)
11.4
Is the first collision of the ball with the floor elastic or inelastic? Give a reason for
your answer.
(2)
[13]
QUESTION 12: 10 Minutes (Taken from DoE FEB/MARCH 2010)
A supervisor who is 1,8 m tall, visits a construction site. A brick resting at the edge of a roof
50 m above the ground suddenly falls. At the instant when the brick has fallen 30 m the
supervisor sees the brick coming down directly towards him from above.
Ignore the effects of friction and take the downwards motion as positive.
12.1
Calculate the speed of the brick after it has fallen 30 m.
© Gauteng Department of Education
(3)
12.2
24 The average reaction time of a human being is 0,4 s. With the aid of a suitable
calculation, determine whether the supervisor will be able to avoid being hit by
the brick.
(6)
[9]
QUESTION 13: 20 Minutes (Taken from DoE FEB/MARCH 2010)
During an investigation a police officer fires a bullet of mass 15 g into a stationary wooden
block, of mass 5 kg, suspended from a long, strong cord. The bullet remains stuck in the
block and the block-bullet system swings to a height of 15 cm above the equilibrium
position, as shown below. (Effects of friction and the mass of the cord may be ignored.)
15 g 13.1
13.2
13.3
13.4
5 kg 15 cm State the law of conservation of momentum in words.
(2)
Use energy principles to show that the magnitude of the velocity of the
block- bullet system is 1,71 m·s-1 immediately after the bullet struck the block.
(3)
Calculate the magnitude of the velocity of the bullet just before it strikes the
block.
(4)
The police officer is pushed slightly backwards by the butt of the rifle, which
he is holding against his shoulder, whilst firing the rifle. Use the relevant law of motion
to explain why this happens.
(3)
[12]
© Gauteng Department of Education
25 EXTRA SESSION NO: 3
TOPIC: ACIDS AND BASES / ELECTROCHEMISTRY
TYPICAL EXAM QUESTIONS
MULTIPLE CHOICE QUESTIONS: (Taken from various DBE Exam Q Papers)
Four possible options are provided as answers to the following questions. Each
question has only ONE correct answer. Write only the letter (A to D) next to the
question number. (1 -20)
1.
Consider the reaction represented by the equation below:
H3PO4(aq) + HCO 3−(aq) ⇌ H2PO 4−(aq) + H2CO3(aq)
Ka > 1
The strongest base in the above reaction is:
A.
H2PO 4 B.
HCO 3−
C.
H3PO4
D.
H2CO3
2.
In the reaction between HCO3 – and OH- , a conjugate acid-base pair is:
A.
HCO3- and H2CO3
B.
HCO3- and OHC.
H2CO3 and H2O
D.
HCO3 – and CO32-
3.
A substance that ionises almost completed in water and donates protons. The
statement describes :
A.
A strong acid.
B.
A weak acid.
C.
A strong base.
D.
A weak base.
4.
Solutions of concentration 0,1 mol. dm-3 are compared for pH value. Which one will
have the highest pH value?
A.
HNO3
B.
CH3COOH
C.
KOH
D.
NH3
5.
A substance has a Ka value of 1,8 x 10-5. The substance could be:
A.
NH3
B.
HNO3
C.
CH3COOH
D.
KOH
© Gauteng Department of Education
26 6.
A solution has a pH > 11. The hydronium ion concentration in the in the solution (in
mol.dm-3) could be:
A.
1 x 10-11
B.
4 x 10-10
C.
5 x 10-3
D.
2,5 x 10-4
7.
The pH of a solution of nitric acid of concentration 0,02 mol.dm-3 is :
A.
1,70
B.
2,25
C.
8,90
D.
11,26
8.
The concentration of hydroxyl ions in a basic solution is 0,01 mol.dm-3. Determine the
pH of the solution.
A.
5
B.
7,6
C.
12
D.
13,8
9.
Propanoic acid (CH3CH2COOH) has a Ka value of 2,3 x 10-6. Is this a strong or weak
acid?
A.
strong
B.
weak
10.
Consider the following acid-base reaction:
H2SO4 + H2O à HSO4- + H3O+
10.1
Examples of ampholytes are:
A.
H2SO4 and H2O
B.
H2O and HSO4C.
H2SO4 and HSO4D.
H2O and H3O+
10.2
The TWO conjugate acid-base pairs are :
A.
H2SO4 and HSO4- ; H2O and H3O+
B.
H2SO4 and H2O ; H3O+ and HSO4-
11.
A certain metal X, can reduce Zn2+ ions to Zn , but not Ba2+ ions to Ba. The metal
could be :
A.
Ag
B.
Fe
C.
Mg
D.
Pb
12.
Consider an electrochemical cell consisting of a silver electrode and iron electrode.
The half-reaction taking place at the ANODE is :
A.
Ag à Ag+ + eB.
Fe
à Fe2+ + 2e-
© Gauteng Department of Education
27 C.
D.
Ag + + e- à Ag
Fe2+ + 2e- à Fe
13.
Sacrificial electrodes are used on the hulls of ships as protection against corrosion
and corrode before the iron does. Most of the metal making up the hull of a ship is iron
. Which one of the following metals would be most suitable for use as a sacrificial
anode on ships’ hulls?
A. Silver
B. Copper
C. Tin
D. Magnesium
14.
Standard electrode potentials are determined by comparison with the standard
hydrogen electrode. An Ag/Ag+ half-cell is connected to a standard hydrogen
electrode. The equation for the half-reaction that occurs at the anode of this cell is :
A.
2H+ + 2e- à H2
B.
H2 à 2H+ + 2eC.
Ag+ + e- à Ag
D.
Ag à Ag+ + e-
15.
The term ‘ redox reaction’ describes a chemical reaction in which :
A.
A transfer of electrons occurs.
B.
A transfer of protons occurs.
C.
Electrons are only given off.
D.
Electrons are only taken in.
16.
Which one of the following chemical reactions is NOT spontaneous?
A.
Zn + 2H+ à Zn2+ + H2
B.
Mg + Fe2+ à Mg2+ + Fe
C.
2Ag + Cu2+ à 2Ag+ + Cu
D.
Cu + H2 à Cu2+ + 2H+
17.
Which ONE of the following CANNOT act as a reducing agent?
A.
Mg
B.
Br−
C.
Fe2+
D.
MnO4−
18.
A sample of silver contains impurities of gold. During purification by electrolysis, the
impure silver is used as an electrode.
Which ONE of the following is the best choice of anode and cathode for this
process?
A.
B.
C.
D.
CATHODE
Pure gold
Impure silver
Pure silver
Impure silver
ANODE
Impure silver
Pure gold
Impure silver
Pure silver
© Gauteng Department of Education
19.
28 The net (overall) cell reaction taking place in a certain cell is
represented as follows:
2H2O(ℓ) + electrical energy → 2H2(g) + O2(g)
Which ONE of the following statements best describes this cell?
The cell is a/an …
A.
electrolytic cell in which an exothermic reaction occurs.
B.
electrolytic cell in which an endothermic reaction occurs.
C.
galvanic (voltaic) cell in which an exothermic reaction occurs.
D.
Galvanic (voltaic) cell in which an endothermic reaction occurs.
20.
When the net (overall) cell reaction in a galvanic (voltaic) cell reaches
equilibrium, the emf of the cell is equal to....
A. +2,00 V.
C. 0,00 V.
21.
B. +1,00 V.
D. -1,00 V.
Copper chloride solution undergoes electrolysis as represented in the simplified
diagram below.
Cu Cl2 Which ONE of the following statements is CORRECT for this process?
A.
Cu is oxidised at the negative electrode.
B.
Cu is reduced at the positive electrode.
C.
Cu2+ ions are reduced at the positive electrode.
D.
Cu2+ ions are reduced at the negative electrode.
22.
The major products formed in the chlor-alkali industry are ...
A.
chlorine gas and sodium hydroxide.
B.
chlorine gas and sodium chloride.
C.
hydrogen chloride gas and sodium hydroxide.
D.
chlorine gas and hydrogen chloride gas.
(22 x 2) = [44]
© Gauteng Department of Education
29 LONG QUESTIONS:
QUESTION 1: 21 minutes (Adapted from DBE Exemplar 2014 Paper 2)
A Grade 12 class wants to determine the percentage of ethanoic acid in a certain
bottle of vinegar. They titrate a sample taken from the bottle of vinegar with a
standard solution of sodium hydroxide. The equation for the reaction is:
CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(ℓ)
1.1
1.2
1.3
1.4
Define an acid in terms of the Arrhenius theory.
(2)
Give a reason why ethanoic acid is classified as a weak acid.
(2)
Explain the meaning of standard solution.
(2)
Write down the names of TWO items of apparatus needed to measure accurate
volumes of the acid and the base in this titration.
(2)
1.5
It is found that 40 mℓ of a 0,5 mol·dm-3 sodium hydroxide solution is needed to
neutralise 20 mℓ of the vinegar.
Calculate the:
1.5.1
pH of the sodium hydroxide solution.
1.5.2
Percentage of ethanoic acid by mass present in the vinegar
(Assume that 1 mℓ of vinegar has a mass of 1 g.)
(3)
(5)
[16]
QUESTION 2: 20 minutes
(Taken from IEB Prelim 2008 Paper 2)
A titration is performed to determine the percentage ethanoic acid per mass in
household vinegar. NaOH solution with a concentration of 0,1 mol.dm-3 is used. A
vinegar solution is prepared by dissolving 20 g vinegar in water, diluted to 100 cm3.
30 cm3 of this solution is neutralized by using 34 cm3 of the NaOH solution.
The balanced equation is as follows :
CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(ℓ)
2.1
2.2
2.3
Name a suitable indicator used for this titration.
Calculate the concentration of the acid solution in mol.dm-3.
Calculate the percentage of the ethanoic acid in household vinegar.
QUESTION 3: 23 minutes
( Taken from DBE March 2011 Paper 2)
The diagram below represents a galvanic (voltaic) cell functioning under standard
conditions with magnesium and silver as electrodes. A voltmeter connected across the
electrodes shows an initial reading of 3,17 V.
© Gauteng Department of Education
(1)
(3)
(5)
[9]
30 V Mg(s) Ag(s) salt bridge Mg2+(aq) 3.1
3.2
3.3
3.4
3.5.
3.6.
3.7
3.8
Ag+(aq
) State the energy conversion that takes place in this cell.
(2)
State TWO standard conditions under which this cell operates.
(2)
Identify the anode of this cell. Explain your answer.
(3)
+
How will an increase in the concentration of the Ag ions influence the
current that the cell delivers? Write down only INCREASES, DECREASES
or REMAINS THE SAME and explain the answer.
(3)
In which direction will electrons flow in this galvanic (voltaic) cell?
(2)
Name two functions of the salt bridge in this cell.
(2)
Write down the two half reactions taking place at the anode and cathode and
the complete cell reaction in this cell.
(6)
Calculate the cell’s emf.
(3)
[23]
QUESTION 4: 15 minutes ( DBE Nov 2012 Paper 2)
The electrochemical cell shown below functions at standard conditions.
V Cu Cu 2+ ( aq) 4.1
4.2
4.3
A ℓ salt bridge A ℓ 3 + ( aq) Which electrode (Cu or Aℓ) is the anode? Explain your choice.
What happens to the concentration of the Aℓ3+ ions in the one beaker?
Write only INCREASES / DECREASES or REMAINS THE SAME.
Explain your answer.
Calculate the emf of this cell.
© Gauteng Department of Education
(3)
(3)
(3)
4.4
4.5
31 The salt bridge is now removed.
What will the reading on the voltmeter be?
Explain your answer.
(3)
Write down the cell notation for this cell.
(3)
[15]
QUESTION 5 : 14 minutes ( DBE Nov 2012 Paper 2 )
The simplified diagram below shows an electrolytic cell used at an electroplating
company to coat iron spoons with silver.
DC power source 5.1
5.2
5.3
5.4
5.5
5.6
5.7
Electrode Y Electrolyte X Iron spoons Write down the energy conversion that takes place in this cell.
Give a reason why direct current (DC) is used in this process.
Which type of reaction (OXIDATION or REDUCTION) takes place at the
spoons?
Give NAME and FORMULA of electrolyte X .
Give a reason why the concentration of electrolyte X remains constant
during electroplating.
Apart from the income generated, write down ONE major reason why the
company electroplates the spoons.
What can be considered major expense(s) for the company during the
process.
(2)
(2)
(2)
(2)
(2)
(2)
(2)
[14]
QUESTION 6: 10 minutes ( DBE March 2011 Paper 2)
Aluminium is one of the most abundant metals on earth, yet it is expensive – largely
because of the amount of electricity needed to extract it. Aluminium ore is called
bauxite. The bauxite is purified to yield a white powder, aluminium oxide, from which
aluminium can be extracted.
The diagram below shows an electrolytic cell used for the extraction of aluminium at
temperatures as high as 1000 °C.
© Gauteng Department of Education
32 Fe container ─ ─ + + Purified aluminium oxide dissolved in molten cryolite (Na 3 AlF 6 ) Carbon electrode Drain Molten aluminium 6.1
6.2
6.3
6.4
6.5
State the energy conversion that takes place in this electrolytic cell.
Is aluminium formed at the positive or negative electrode?
Use the Table of Standard Reduction Potentials (Table 4A or 4B) to write
down the half-reaction for the formation of aluminium.
Explain why carbon dioxide gas is formed at one of the electrodes.
Why should the carbon electrodes be replaced regularly?
(2)
(2)
(2)
(2)
(2)
[10]
EXTRA SESSION NO: 4
TOPIC: ORGANIC CHEMISTRY.
TYPICAL EXAM QUESTIONS
MULTIPLE CHOICE QUESTIONS:
Four possible options are provided as answers to the following questions. Each
question has only ONE correct answer. Write only the letter (A to D) next to the
question number. (1 -20)
1.1
Prop-1-ene is a flammable alkene. Why is prop-1-ene considered to be a dangerous
compound?
A. It contains single bonds only.
B. It is highly flammable.
C. It is a saturated hydrocarbon.
D. It is an alkene.
Through addition reactions, prop-1-ene can be converted to other compounds, such
as alkanes and alcohols.
1.2
Which part of the structure of an alkene allows it to undergo addition reactions?
© Gauteng Department of Education
33 A. the double bond
C. a carbon atom.
B. a hydrogen atom.
D. a single bond.
In one type of addition reaction, prop-1-ene can be converted to an alcohol.
1.3
Name the type of addition reaction that takes place.
A. hydrogenation
B. halogenation
C. hydration
D. hydrohalogenation
1.4.
Write down the name of the catalyst used in this reaction.
A. Hydrochloric acid
B. sulphuric acid
C. platinum
D. copper.
1.5
Name the products formed for the complete combustion of prop-1-ene.
A. carbon dioxide
B. water
C. carbon dioxide and water. D. carbon and water.
1.6
Prop-1-ene can be produced from an alcohol by an elimination reaction.
Name the type of elimination reaction that takes place.
A. dehydrohalogenation
C. dehalogenation
2.
B. cracking
D. dehydration.
Five alcohols represented by the letters A – E are listed in the table below.
A
C
E
Methanol
Propan-1-ol
2-methylpropan-2-ol
B
D
Ethanol
Butan-2-ol
2.1
Which ONE of the above alcohols is a SECONDARY alcohol? Write down only the
LETTER that represents the alcohol.
A. B
B. C
C. D
D. E
2.2
The letter E represents 2-methylpropan-2-ol. For this alcohol, write down the
LETTER in the table that represents one of its structural isomers.
A. B
B. C
C. D
D. E
3.
Three hydrocarbons (A, B and C) with molecular formula C5H12 are used to
investigate the effect of BRANCHING on the BOILING POINTS of hydrocarbons.
The results obtained are shown in the table below.
HYDROCARBON BOILING POINT
(°C)
A
36
B
28
C
10
© Gauteng Department of Education
34 3.1
Write down the term used to describe compounds with the same molecular formula,
but with different structural formulae.
A. isotopes
B. isomers
C. functional groups
D. homologous series
3.2
Write down for this investigation the following:
3.2.1
Dependent variable
A. molecular mass
B. branching
C. boiling points.
Independent variable
A. molecular mass
B. branching
C. boiling points.
Controlled variable
A. molecular mass
B. branching
C. boiling points.
3.2.2
3.2.3
3.3
Are these hydrocarbons saturated or unsaturated?
A. saturated
B. unsaturated
3.4
One of the hydrocarbons (A, B or C) has a straight chain with no branches. Write
down the following:
3.4.1.
The letter (A, B or C) that represents this hydrocarbon
A. B
B. C
C. A
3.4.2
It’s IUPAC name
A. pent-1-ene
4.
5.
B.
pentane
C. pentan-2-ol
Which ONE of the following compounds has the highest melting point?
A.
CH3CH3
B.
CH3CH2CH3
C.
CH3CH2CH2CH3
D.
CH3CH2CH2CH2CH3
Some of the reactions of BUTAN-1-OL are represented in the flow diagram below.
P, Q and R represent the organic products formed.
P Concentrated H 2SO 4 HBr Q BUTAN -­‐ 1 -­‐ OL Ethanoic acid R D. pentanal
© Gauteng Department of Education
35 5.1
Is butan-1-ol a PRIMARY, SECONDARY or TERTIARY alcohol?
A. Primary
B. Secondary
C. Tertiary
5.2.
Product P is formed when butan-1-ol is heated in the presence of concentrated
sulphuric acid.
Write down the name of the type of reaction that takes place
A. dehydration
B. hydrolysis
C. hydration
D. hydrohalogenation
5.3
Product R is formed when butan-1-ol reacts with ethanoic acid in the presence of an
acid catalyst. Write down the name of the type of reaction that takes place.
A. esterification
B. addition
C. substitution
D. elimination
6.
7.
Consider the flow diagram below:
propene
H2
Compound X
Pt
The IUPAC name for compound X is:
A
propyne
B
propan-1-ol
C
propane
D
propan-2-ol
© Gauteng Department of Education
36 8.
23 x 2
= [46]
LONG QUESTIONS:
QUESTION : 1 Time: 13 ( Taken from DBE March 2014 Paper 2)
Petrol is a mixture of hydrocarbons, many of which have the molecular formula C8H18.
4.1 Write1.1
Write down the name of the homologous series to which hydrocarbons with this
molecular formula belong.
The structures of two compounds with molecular formula C8H18 are given below.
© Gauteng Department of Education
(1)
1.2
1.3
37 Why are compounds A and B structural isomers?
Which ONE of the above compounds (A or B) has a higher boiling point?
Refer to MOLECULAR STRUCTURE, INTERMOLECULAR FORCES and the
ENERGY NEEDED to explain the answer.
(2)
(4)
Compounds A and B can be used to prepare smaller hydrocarbons at high
temperatures in the presence of a catalyst. One such reaction is represented by the
incomplete equation below.
C8H18 → C5H12 + compound C
1.4
1.5
1.6.
Write down the:
Name of the reaction represented above.
Structural formula of compound C.
Balance the equation, using molecular formulae, for the complete combustion
of C5H12
(1)
(2)
(3)
[13]
QUESTION 2; Minutes 17 (Taken from DBE March 2014 Paper 2)
The flow diagram below shows the steps that a learner follows to convert but-1-ene to
but-2-ene:
But -­‐ 1 -­‐ ene Compound X ( Major product) Compound Z CH 3CH(OH)CH 2CH 3 But -­‐ 2 -­‐ ene 2.1
Write down the structural formula of the functional group of but-1-ene.
(1)
2.2
2.2.1
2.2.2.
Compound X is formed when but-1-ene reacts with HCℓ(g).
Name the type of reaction that takes place.
Write down the structural formula of compound X.
(1)
(2)
2.3
2.3 1
2.3.2
Compound X is converted to alcohol Z.
Name the type of reaction that takes place.
(1)
Write down the NAME or FORMULA of another reactant needed for this reaction. (3)
2.4
2.4.1
2.4.2
2.4.3
Compound Z is converted to but-2-ene in the presence of concentrated sulphuric acid.
Is compound Z a PRIMARY, SECONDARY or TERTIARY alcohol?
(1)
Name the type of reaction that takes place.
(1)
What is the role of sulphuric acid in this reaction?
(1)
© Gauteng Department of Education
2.5
38 Another learner discovers that but-2-ene can be prepared using the following
incomplete reaction below.
Compound X + (a) → but-2-ene + (b) + (c)
2.5.1
2.5.2
2.5.3
Write down the:
Type of reaction that takes place.
Conditions needed for this reaction to take place.
FORMULAE of the reactant and products represented by each of the letters
(a), (b) and (c) respectively.
(1)
(2)
(3)
[17]
QUESTION 3: 14 Minutes (Taken from DBE March 2008 Paper 2)
Some organic reactions are shown in the flow diagram below.
X Br2 A UV light C3H7 OH propan-­‐1-­‐ol B C3H7Br 1-­‐bromopropane D C C3H7OH propan-­‐1-­‐ol concentrated KOH(aq) heat Y 3.1
3.2
3.3
3.4
3.5
Name the type of reactions illustrated by A, B, C and D.
Use condensed structural formulae and write a balanced equation for reaction
C.
Write down the structural formula for compound X.
In order to obtain product Y, C3H7Br is heated with a concentrated solution of
KOH under reflux. Use condensed structural formulae to write a balanced
equation for the reaction.
A group of learners decided to heat C3H7Br with dilute sodium hydroxide,
instead of the concentrated potassium hydroxide, under reflux. Write down
the IUPAC name of the organic compound that they will obtain.
© Gauteng Department of Education
(4)
(3)
(2)
(3)
(2)
[14]
39 QUESTION 4:
12 Minutes (taken from DBE Nov 2012 paper 24.1.
The flow diagram below shows how three organic compounds can be prepared from
2-bromo-3-methylbutane:
Compound B Compound A Reaction 1 Reaction 2 2 -­‐ bromo -­‐ 3 -­‐ methylbutane Reaction 3 An alkene Write down:
Homologous series to which 2-bromo-3-methylbutane belongs
Structural formula of 2-bromo-3-methylbutane
(1)
(2)
4.2.1
4.2.2
Reaction 2 takes place in the presence of a dilute sodium hydroxide solution.
Write down the:
Name of the type of reaction which takes place.
Structural formula of compound B.
(1)
(2)
4.3
Reaction 1 takes place in the presence of concentrated sodium hydroxide.
4.3.1
4.3.2
4.3.3
Write down:
Another reaction condition needed for this reaction.
The name of the type of reaction which takes place.
The structural formula of compound A, the major product formed.
4.1.1
4.1.2
4.2
4.4
Reaction 3 takes place when compound B is heated in the presence of
concentrated sulphuric acid. Write down the IUPAC name of the major
product formed.
© Gauteng Department of Education
(1)
(1)
(2)
(2)
[12]
40 QUESTION 5: 14 Minutes (Taken from DBE Nov 2012 Paper 2)
During a practical investigation the boiling points of the first six straight-chain ALKANES were
determined and the results were recorded in the table below.
ALKANE
Methane
Ethane
Propane
Butane
Pentane
Hexane
MOLECULAR BOILING POINT
FORMULA
(°C)
CH4
−164
C2H6
−89
C3H8
−42
C4H10
−0,5
C5H12
36
C6H14
69
5.1
5.1.1
5.1.2
Write down the:
Most important use of the alkanes in the above table.
General formula of the alkanes.
(1)
(1)
5.2
5.2.1
5.2.2
5.2.3
For this investigation, write down the following:
Dependent variable
Independent variable
Conclusion that can be drawn from the above results
(1)
(1)
(2)
5.3
Write down the NAME of an alkane that is a liquid at 25 °C.
(1)
5.4
Alkanes burn readily in oxygen. Write down a balanced equation, using molecular
formulae, for the combustion of propane in excess oxygen.
(3)
5.5
Will the boiling points of the structural isomers of hexane be HIGHER THAN,
LOWER THAN or EQUAL TO that of hexane? Refer to MOLECULAR
STRUCTURE, INTERMOLECULAR FORCES and ENERGY NEEDED to
explain the answer.
(4)
[14]
QUESTION 6: 22 Minutes (Taken from DBE March 2011 Paper 2)
Prop-1-ene, an UNSATURATED hydrocarbon, and compound X, a SATURATED
hydrocarbon, react with chlorine, as represented by the incomplete equations below.
Reaction I:
Prop-1-ene + Cℓ2 →
Reaction II:
X + Cℓ2 → 2-chlorobutane + Y
6.1
6.1.1
Give a reason why prop-1-ene is classified as unsaturated.
© Gauteng Department of Education
(1)
6.1.2
41 What type of reaction (ADDITION or SUBSTITUTION) takes place in the following:
(a)
(b)
Reaction I
Reaction II
(1)
(1)
6.1.3
6.1.4
6.1.5
6.1.6
Write down the structural formula of the product formed in Reaction I.
Write down the reaction condition necessary for Reaction II to take place.
Write down the IUPAC name of reactant X.
Write down the name or formula of product Y.
6.2
2-chlorobutane can either undergo ELIMINATION or SUBSTITUTION in the presence
of a strong base such as sodium hydroxide.
6.2.1
Which reaction will preferably take place when 2-chlorobutane is heated in the
presence of CONCENTRATED sodium hydroxide in ethanol? Write down only
SUBSTITUTION or ELIMINATION.
(1)
Write down the IUPAC name of the major organic compound formed in
QUESTION 6.2.1.
(2)
Use structural formulae to write down a balanced equation for the reaction that
takes place when 2-chlorobutane reacts with a DILUTE sodium hydroxide solution.(6)
Write down the name of the type of substitution reaction that takes place in
QUESTION 6.2.3.
(1)
6.2.2
6.2.3
6.2.4
6.3
6.3.1
6.3.2
Haloalkanes are used in insecticides (insect killers).
Write down ONE POSITIVE impact of insecticides on human development.
Write down ONE NEGATIVE impact of insecticides on humans.
© Gauteng Department of Education
(2)
(1)
(1)
(1)
(2)
(2)
[22]
42 EXTRA SESSION NO: 5
TOPIC: REACTION RATES AND CHEMICAL EQUILIBRIUM.
TYPICAL EXAM QUESTIONS
MULTIPLE CHOICE QUESTIONS:
Four possible options are provided as answers to the following questions. Each
question has only ONE correct answer. Write only the letter (A to D) next to the
question number. (1 -20)
1.
The rate of reaction increases as the temperature increases. Which one of the
following statements provides the best explanation for this?
A.
At lower temperatures the particles do not collide with each other.
B.
At higher temperatures the particles have more kinetic energy, move
faster and collide more often.
C.
Increasing the temperature increases the number of particles, so they
collide more often.
D.
Increasing the temperature lowers the activation energy.
2.
Which one of the following statements about collisions is correct?
A.
All colliding particles have the same amount of energy.
B.
Only fast moving particles collide with each other.
C.
Chemical reactions can only occur if the colliding particles have enough
energy.
D.
Collisions depend on the type of chemicals reacting.
3.
Chemical reactions eventually stop. What is generally the reason for this?
A.
The catalyst has been used up.
B.
The particles have run out of energy.
C.
One or more of the reactants has been used up.
D.
Chemical equilibrium is reached.
4.
In the reaction with hydrochloric acid , powdered magnesium reacts faster than
the same mass of magnesium ribbon. Why is this?
A.
The powdered magnesium contains more atoms than the magnesium
ribbon.
B.
The powdered magnesium is hotter than the magnesium ribbon.
C.
The powered magnesium has a bigger surface area than the
magnesium ribbon.
D.
The concentration of the powered magnesium is greater.
5.
Marble reacts with HCl to produce CaCl2 , H2O and CO2. In which of these
mixtures is the rate of reaction likely to be the greatest?
A.
1 g of marble chips in 100 cm3 of HCl of concentration 1 mol.dm-3 at 20!
C.
B.
1 g of powered marble in 100 cm3 of HCl of concentration 1 mol.dm-3 at
30! C.
© Gauteng Department of Education
43 C.
D.
1 g of powered marble in 100 cm3 of HCl of concentration 1 mol.dm-3 at
20! C.
1 g of marble chips in 200 cm3 of HCl of concentration 1 mol.dm-3 at 20!
C.
6.
Manganese dioxide is a black powder that catalyses the breakdown of
hydrogen peroxide to water and oxygen. Which one of the following statements
is correct?
A.
The mass of magnesium dioxide will stay the same during the reaction.
B.
The catalysed reaction will produce more oxygen than the uncatalysed
reaction.
C.
The particles in the catalysed reaction will have more energy than in the
uncatalysed reaction.
D.
The mass of manganese dioxide will decrease during the reaction.
7.
Activation energy can best be described as the minimum energy required to
A.
cause effective collisions.
B.
make reactant molecules collide.
C.
increase the kinetic energy of reactant molecules.
D.
change the orientation of reactant molecules.
8.
The rate of a chemical reaction can be expressed in ………
A.
grams per mole.
B.
energy consumed per mole.
C.
volume of gas formed per unit time.
D.
moles of product formed per litre of solution.
9.
Which one of the following is NOT a factor that influence a chemical reaction
rate?
A.
Pressure
B.
Catalyst
C.
Temperature
D.
Concentration
10.
Consider the following reaction taking place in an open vessel at a certain
temperature:
2H2O2 (aq) à 2H2O (l) + O2 (g) ΔH < 0
A.
B.
C.
D.
E.
The initial reaction rate of the above reaction may be DECREASED by
A . adding O2 gas to the system.
B. adding MnO2 as a catalyst.
C. cooling the system.
D. increasing the pressure on the system.
11.
When the enthalpy of a chemical reaction increases……..
A.
ΔH is negative.
B.
the reaction is endothermic.
C.
the temperature in the reaction vessel will increase.
D.
the reaction cannot take place spontaneously.
© Gauteng Department of Education
44 12.
The addition of a catalyst to a chemical reaction lowers the…….
A.
activation energy required for the reaction to occur.
B.
chemical energy of the products.
C.
chemical energy of the reactants.
D.
value of the enthalpy change for the reaction.
13.
Which of the following changes in the table below will take place if the
temperature of a reaction mixture is increased?
(i)
(ii)
(iii)
The rate of the reaction increases
The frequency of the collisions increases
The average kinetic energy of particles in the reaction mixture increases
A.
B.
C.
D.
(i) and (ii) only
(ii) and (iii) only
(i) and (iii) only
(i) , (ii) and (iii)
14.
Phosphorus ignites spontaneous and releases large amounts of energy. This
reaction is …….
A.
Endothermic
B.
Exothermic
15.
Which ONE of the following graphs shows the relationship between activation
energy (Ea) of a reaction and temperature?
A E a
0 C E a 0 B E a
0 Temperature Temperature D E a Temperature Temperature 0 © Gauteng Department of Education
45 16.
Consider the chemical reaction represented by the equation below.
CaCO3(s) + 2HCℓ(aq) → CaCℓ2(aq) + CO2(g) + H2O(ℓ)
Which ONE of the following changes will increase the rate of production of
CO2(g)?
A.
B.
C.
D.
17.
Increase in pressure
Increase in mass of CaCO3
Increase in volume of HCℓ(aq)
Increase in concentration of HCℓ(aq)
The diagram below shows the change in potential energy for a hypothetical
reaction, represented by the following equation:
X2 (g) + 3Y2(g) → 2XY3
Potential energy (k) 180 kJ X 2 + 3Y 2 80 kJ 2 XY 3 reaction coordinates
The activation energy for the forward reaction is…
A.
- 80 kJ
B.
80 kJ
C. 100 kJ
D. 180 kJ
© Gauteng Department of Education
46 Kinetic energy
Number of particles 18. The energy distribution diagrams for particles in a fixed mass of gas at two
different temperatures, T1 and T2, are shown below.
T 1 T 2 Which ONE of the following is the correct nterpretation of the diagrams as the
temperature of the gas changes from T1 to T2?
Activation energy (EA)
Number of effective
collisions
A
Remains the same
Increases
B
Decreases
Decreases
C
Decreases
Increases
D
Remains the same
Decreases
19.
Which ONE of the following statements about the rate of reaction is
INCORRECT A.
Meat decays faster in a warm environment than in a fridge.
B.
Most industrial processes are cheaper to run when a catalyst is used.
C.
Zinc reacts faster with excess dilute hydrochloric acid that is not in
excess.
D.
Potatoes cook faster when sliced than when cooked whole.
20.
The equation below represents a chemical reaction at equilibrium in a closed
container.
H2(g) + I2(g) ⇌ 2HI(g) DH < 0
Which ONE of the following changes will increase the yield of HI(g) in the above
reaction?
A.
B.
Increase the temperature
Decrease the temperature
© Gauteng Department of Education
47 C.
D.
21.
Increase the pressure by decreasing the volume
Decrease the pressure by increasing the volume
The expression for the equilibrium constant (KC) of a hypothetical reaction is
given as follows:
KC = [C] [D]2
Which ONE of the following equations for a reaction at equilibrium matches the
above expression?
A.
B.
C.
D.
22.
A chemical reaction reaches equilibrium. Which ONE of the following
statements regarding this equilibrium is TRUE?
A.
B.
C.
D.
23.
3A(s) ⇌ C(g) + 2D(g)
3A(ℓ) ⇌ C(aq) + 2D(aq)
3A(aq) + B(s) ⇌ C(g) + D2(g)
3A() + B(s) ⇌ C(aq) + 2D(aq)
The concentrations of the individual reactants and products are
constant.
The concentrations of the individual reactants and products are equal.
The concentrations of the individual reactants are zero.
The concentrations of the individual products increase until the reaction
stops.
The reaction represented by the balanced equation below reaches equilibrium
in a closed container.
2NO2(g) ⇌ N2O4(g) ΔH < 0
Which ONE of the following changes will INCREASE the yield of N2O4(g)?
A. Add a catalyst.
24.
B.
Remove NO2 gas from the container.
C.
Increase the temperature of the system.
D.
Decrease the temperature of the system.
Initially, a certain amount of ICℓ(g) is sealed in an empty flask at a certain
temperature. The reaction that takes place is:
2ICℓ(g) ⇌ I2(g) + Cℓ2(g)
Which of the following statements describe(s) the change(s) occurring as the
system proceeds towards equilibrium?
© Gauteng Department of Education
48 i.
ii.
iii.
A.
B.
C.
D.
The rate of the reverse reaction increases.
The concentration of ICℓ(g) increases.
The concentration of Cℓ2(g) increases.
(i) only
(ii) only
(i) and (iii) only
(ii) and (iii) only
24 x (2) = [48]
LONG QUESTIONS:
QUESTION 1: 16 minutes (Taken from DBE March 2011 Paper 2)
Learners perform three investigations (A, B and C) to study three factors which affect
the rate of chemical reactions. They use the reaction between solid calcium carbonate
(CaCO3) and excess hydrochloric acid (HCℓ) solution, represented by the balanced
equation below, in all three investigations.
CaCO3(s) + 2HCℓ(aq) → CaCℓ2(aq) + H2O(ℓ) + CO2(g)
EXCESS HYDROCHLORIC ACID is used and the calcium carbonate is COMPLETELY
COVERED in all the investigations.
INVESTIGATION A:
The learners conduct two experiments using the conditions as shown in the table below.
Experiment 1
Experiment 2
Mass
of
CaCO3
(g)
2
2
State of
CaCO3
Concentration of
HCℓ (mol·dm-3)
Temperature
of HCℓ (°C)
powder
lumps
0,2
0,2
25
25
1.1. Which factor influencing reaction rate is investigated?
(1)
1.2. Write down an INVESTIGATIVE QUESTION for this investigation
(2)
1.3. The learners now repeat Experiment 1, but use 4 g of calcium carbonate in
excess acid, instead of 2 g. They find that the rate of the reaction
INCREASES.
Give a reason why the rate increases.
(2)
© Gauteng Department of Education
49 INVESTIGATION B:
The learners conduct two experiments using the conditions as shown in the table
below.
Mass of
CaCO3
(g)
2
2
Experiment 3
Experiment 4
State
of
CaCO3
lumps
lumps
Concentration
of HCℓ
(mol·dm-3)
0,2
1,0
Temperature
of HCℓ (°C)
25
25
1.4. Identify the independent variable in this investigation.
(1)
1.5. Write down a hypothesis for this investigation.
(2)
1.6. Is it fair to compare results obtained in Experiment 3 with that in Experiment
4? Give a reason for the answer.
(2)
1.7. The reactions in Experiments 3 and 4 both run to completion. How will the
yield of CO2(g) in Experiment 3 compare to that in Experiment 4? Write
down only LARGER THAN, SMALLER THAN or EQUAL TO and give a
reason for the answer.
(2)
INVESTIGATION C:
The learners conduct two experiments using the conditions as shown in the table
below.
Mass of
CaCO3 (g)
Experiment 5
Experiment 6
4
4
State of
CaCO3
powder
powder
Concentration
of HCℓ (mol·dm3
)
0,2
0,2
Temperature of
HCℓ (°C)
25
35
1.8. How does the average kinetic energy of the particles in the reaction in
Experiment 5 compare to that in Experiment 6? Write down only HIGHER
THAN, LOWER THAN or EQUAL TO.
(1)
1.9. On the same set of axes, draw sketch graphs of the number of molecules
versus the kinetic energy (Maxwell-Boltzmann distribution curves) for each of
Experiment 5 and Experiment 6.
Label the axes.
Clearly label each graph as Experiment 5 or Experiment 6
(3)
[16]
QUESTION 2: 16 minutes (Taken from DBE March 2011 Paper 2)
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 < 0
To 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.
© Gauteng Department of Education
50 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.
N2 H2 NH3 0 t1 t2 t3 2.1
Identify the changes made to the equilibrium mixture at each of the following
times:
2.1.2
t2
(2)
2.1.3
t3
(2)
2.1.4 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)
2.2.
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.
Calculate the value of the equilibrium constant (Kc) at 450 °C.
© Gauteng Department of Education
(9)
[ 17]