Page 1 of 15 ST STITHIANS COLLEGE
DEPARTMENT OF PHYSICAL SCIENCE
PRELIMINARY EXAMINATIONS 2012
GRADE 12 PHYSICAL SCIENCE: PAPER 2
Examiners
Moderators:
Miss S Nargaroo (Girls’ College), Mr SB Lambson
Mr SB Lambson
Maximum time:
3 hours (+ 10 minutes reading time)
Marks:
200
INSTRUCTIONS
1. This paper consists of FIFTEEN (15) pages. Please ensure that you have all of them
2. Read the questions carefully.
3. Answer the questions in the answer booklet provided
4. Graph paper is provided
5. It is in your own interest to write legibly and to present your work neatly.
6. Ensure that the numbering of the questions is correct.
7. Show all your workings, where necessary.
8. A data sheet is provided which may be used to assist you in answering the questions Page 2 of 15 QUESTION ONE - Multiple Choice
In each of the following questions 4 possible answers are provided. Write down only the number
of the question and the letter of the corresponding answer.
1.1.
Compound X is mixed with bromine water. The brown colour of the bromine disappears
almost immediately. Which one of the following represents compound X?
A.
B.
C.
D.
1.2.
Which one of the following is not a property or characteristic of the hydrocarbons?
A.
B.
C.
D.
1.3.
C2 H4
C 3 H8
CH3OH
C2 H 6
They can undergo combustion reactions
They comprise of only two different types of elements.
They are non polar molecules.
They are reactive molecules.
What is the IUPAC name of the following compound?
H
A.
B.
C.
D.
.
H
H
C
C
C
CH3
H
CH3
2,4-dimethyl but-1-ene
1,3-dimethyl but-1-ene
1,3-methyl but-1-ene
2-methyl pentene
H
C
H
Page 3 of 15 1.4.
In a series of experiments 0,05g samples of magnesium were added separately to
100cm3 volumes of hydrochloric acid. The table below summarises the experimental
conditions:
Expt
Mg(s)
i
ii
iii
iv
v
ribbon
ribbon
powder
powder
powder
HCl(aq)
(mol.dm3)
0,1
0,5
0,1
0,5
0,1
Temp of acid(°C)
25
25
70
25
20
Which of the combination of experiments would magnesium be expected to take the least
amount of time to completely react with the excess hydrochloric acid?
A.
B.
C.
D.
1.5.
I and ii
iii and iv
iii and v
ii and iv
The rate of the reaction between zinc granules and dilute sulphuric acid can be increased
by adding a solution of copper sulphate. The reason for this is that the……
A.
B.
C.
D.
1.6.
Zinc displaces the copper from the copper sulphate.
Sulphuric acid reacts more vigorously with the copper.
Concentration of the sulphate ions increases.
Copper ions act as a catalyst.
One of the stages in the industrial preparation of iron from its ore is represented by the
equation below:
Fe2O3(s) + 3CO (g)
2Fe (l)
+ 3CO2 (g)
ΔH<0
The following possible disturbances can be made to the equilibrium system:
(i)
(ii)
(iii)
Pressure may be increased.
CO2 may be removed.
Temperature may be increased
Which of the changes mentioned above will favour the forward reaction?
A.
B.
C.
D.
(i), (ii) and (iii)
(i) and (ii) only
(ii) only
(iii) only
Page 4 of 15 1.7.
Consider the following reactions with a metal M.
(i)
(ii)
M reacts with a solution of AgNO3 , causing a deposit of metallic Ag to
form.
M does not react with a solution of ZnSO4.
The correct way to list the metals M, Ag and Zn in order of decreasing strength as
reducing agents is:
A.
B.
C.
D.
1.8.
M, Ag, Zn
Zn, M, Ag
Ag, M, Zn
Ag, Zn, M
The most common filling for tooth cavities is “dental amalgam” – a solid solution of tin
and silver in mercury. If you bite on a piece of aluminium foil that is in contact with a
dental filling in your mouth, you may feel a painful sensation because………
A. the aluminium foil is hard.
B. a temporary galvanic cell has been set up whilst the aluminium and filling are in
contact.
C. electrons are being transferred to the aluminium.
D. a temporary electrolytic cell has been set up whilst the aluminium and filling are in
contact.
1.9
Consider the following redox reaction:
Br2 (l) + 2I – (aq) → 2Br – (aq) + I2 (s)
Which one of the following deductions about this reaction is correct?
A.
B.
C.
D.
bromine is oxidised.
bromine acts as a reducing agent.
the iodide ions are oxidised.
iodine acts as a reducing agent.
Page 5 of 15 1.10
The diagram below shows the energy distribution curves for molecules of a sample of a
liquid at two different temperatures.
Which of the following statements about the graph is incorrect?
A
At T2 the number of molecules with greater Ek is decreased.
B
At T1 the number of molecules with greater Ek is decreased.
C
The shaded area represents the number of molecules with enough energy to
react.
D Temperature of a substance is related to the kinetic energy of the molecules. 20 marks
Page 6 of 15 QUESTION TWO
2.1
2.2
2.3
Provide definitions for the following:
2.1.1 homologous series.
(2)
2.1.2 hydrogenation.
(2)
Draw structures for the following organic compounds:
2.2.1 3 dimethyl, pent-1-yne.
(structural formula)
(2)
2.2.2 propan-1,2,3-triol.
(condensed formula)
(2)
2.2.3 methyl pentanoate.
(semi-structural formula)
(2)
Propane and butane are used as propellants in spray cans in place of chloflourocarbons
(CFCs).
2.3.1 Name the homologous series to which both propane and butane belong
and give the general formula of this series.
(2)
2.3.2 The molecule butane can be found in nature in another isomeric form
(a)
What is meant by the term ‘isomeric form’ ?
(2)
(b)
Draw the semi-structural formula and name the other isomeric
form of butane.
(3)
The two isomers will have distinctly different boiling points.
Which isomer will have the greater boiling point ? Explain your
reasoning.
(4)
(c)
Page 7 of 15 2.3.3
Both propane and butane are able to undergo combustion reactions.
Below is the combustion reaction of propane
C 3 H8
5O2
3CO2
+
4H2O
(a)
What is meant by the term ‘combustion’ ?
(2)
(b)
If 39,2dm3 of propane gas reacts completely, what volume of
CO2 gas would be formed ? (assume all gases are at STP)
(3)
If butane gas has to now react, what mass of butane would be
required to react completely with 53,9dm3 of oxygen gas at STP ?
(5)
(c)
2.4
+
Nowadays newer alternatives to CFC’s are hydrochloroflourocarbons (HCFCs) and
hydroflourocarbons(HFCs) such as CH2FCH3.
2.4.1 Draw the structural formula for CH2FCH3 and give the IUPAC name
for this compound.
(3)
2.4.2 CFC’s have been totally banned from use in society. Briefly explain
why this ban was introduced.
(2)
36 marks
QUESTION THREE
Consider the following organic compounds, all of which contain oxygen in their
structure.
A. CH3COCH3
B. CH3CH2COOH
C. CH3CH2CHO
D. CH3CH2CH2OH
3.1.
Name the homologous series to which compound A belongs
(1)
3.2.
Which compound is an isomer of A?
(1)
3.3
What name is given to the functional group of compound B?
(1)
3.4
Compounds B and D can react together to form an ester.
3.4.1
Name the ester that is formed.
(2)
3.4.2
Name the substance that is added to the reaction which
acts as a dehydrating agent in the reaction.
(1)
3.4.3
Why is it important to add a dehydrating agent in this reaction ?
(3)
3.4.4
Explain why an esterification reaction should always be performed
in a hot water bath and never over an open flame.
(2)
11
marks
Page 8 of 15 QUESTION FOUR
4.1
Polymers are formed by either addition or condensation type reactions. Consider
the semi structural formula of the polymer below:
4.1.1
Define the term polymer
(2)
4.1.2
Would this be an addition or condensation type polymer?
Explain you answer
(3)
4.1.3
Identify the homologous series to which the individual monomers belong
(2)
4.1.4
In terms of propagation of this polymer, what is significant about the
structure of the monomer units that are used in this type polymerisation
reaction ?
(4)
Study the structure of the polymer given above and write down the
semi structural formula of one repeating unit.
(2)
What molecule would be released every time a repeating unit is formed?
(1)
4.1.5.
4.1.6
4.2
Plastics are man made macromolecules and they are divided into two groups,
namely thermosets and thermoplastics. Briefly explain the structural differences
between these two types of plastics.
18 marks
(4)
Page 9 of 15 QUESTION FIVE
A number of basic organic reactions are shown in the flow diagram below.
B
X
C 3 H6
C
Y
+ F2
A
+ Br2
C3H7Br
D
C3H7OH
5.1
Name the type of reactions shown by A, B C and D.
(4)
5.2
Write down the molecular formula for compound X.
(1)
5.3
Using structural formulae, show the product of reaction C.
(2)
5.4
Write down the IUPAC name for compound Y.
(2)
5.5
What homologous series does compound Y belong to?
(1)
10 MARKS
Page 10 of 15 QUESTION 6
Antacids are used to relieve indigestion (the condition when the stomach produces too much
acid resulting in an uncomfortable and painful feeling). A certain antacid tablet dissolves in
water and reacts with the acid in the stomach to release carbon dioxide gas .A group of learners
want to investigate the effect of temperature on the rate of dissolving of this antacid tablet in
water.
Design an investigation that the group of learners can conduct by answering the questions that
follow:
6.1.
State a hypothesis for this investigation.
(2)
6.2
Is it better to take the antacid tablet with warm water or cold water. Give a
reason for your answer.
(2)
6.3.
The active ingredient in most antacid tablets is calcium carbonate which reacts
with the hydrochloric acid in the stomach according to the reaction:
CaCO3(s)
+ 2 HCl (aq)
CaCl2 (aq) + H2O (l) + CO2 (g)
Some students set up an experiment that collected the carbon dioxide gas released and
measured the volume of gas collected every half minute. The results of the experiment
are shown in the table below.
Time (minutes)
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
5,5
Volume of gas(cm3)
0
5
18
24
28
31
33
34
35
35,5
36
36
6.3.1.
Name the independent variable in this experiment.
(1)
6.3.2.
Identify 2 variables that need to be controlled.
(2)
6.3.3.
Plot a graph of gas production versus time on the graph paper provided.
(6)
6.3.4.
At what time did the reaction run to completion?
(1)
Page 11 of 15 6.3.5
6.3.6.
Using molecular collision theory, explain the shape of the graph
between t = 0 and t = 3 minutes.
(4)
If the mass of calcium carbonate in one antacid tablet is 700mg,
calculate the volume of 0,1 mol.dm-3 hydrochloric acid that would be
neutralised by one tablet.
(5)
23 marks
QUESTION SEVEN
Sulphuric acid is made using the industrial process known as the Contact process at 430oC.
This process allows sulphur dioxide to react with oxygen forming sulphur trioxide according
to the equilibrium reaction shown below :
2SO2 (g) + O2 (g)
7.1.
7.2
7.3
2SO3 (g)
∆H= -192kJ.
Does the forward reaction represent an exothermic or endothermic
reaction ? Give a reason for your answer
(2)
Draw a neat energy profile for the forward reaction. Include the following
labels on your profile :
activation energy
energy of products
energy of reactants
activated complex
heat of reaction
energy of product formation
(5)
The Contact process gets its name due the contact that the reactant molecules
make with the surface of a catalyst that is added at the start of the reaction.
7.3.1
Define the term ‘catalyst’
(2)
7.3.2
Using the energy profile drawn in 6.2, draw and explain how the addition
of a catalyst will affect the shape of the profile.
(3)
7.4
Define the term ‘dynamic chemical equilibrium’
7.5
By writing down only the words INCREASE, DECREASE or STAYS THE SAME,
state the effect the following changes will have on the amount of SO2 produced
when the system is at equilibrium.
7.5.1.
SO3 is removed from the reaction vessel
7.5.2.
The temperature of the system is decreased
7.5.3.
The pressure in the system is decreased
7.5.4
More catalyst is added to the system
(3)
(4)
Page 12 of 15 7.6
7.7
7.8
When equilibrium is reached at 4300C, it was found that 0, 2 mol of SO2,
0,4mol of O2 and 0,2mol SO3 were formed in a 2dm3 container.
Calculate the equilibrium constant for this reaction at this temperature.
(4)
By considering the reaction, the best conditions to produce high yields of SO3 are
at low temperatures and high pressures .
7.7.1
Explain why will these conditions are considered to be ideal ?
(4)
7.7.2
Practically, the reaction takes place at the relatively high temperature
of 4300C and a relatively low pressure of 2 atmospheres. Explain why
these less than ideal conditions are actually used in industry.
(4)
Consider the graph shown below which illustrates how the rate of formation of SO3
changes with time in the Contact process.
12 This graph shows the changes in reaction rates for a period of 14 minutes.
7.8.1
What do the solid and broken lies represent on this graph ?
(2)
7.8.2
Why do these lines have the curved shapes as seen on the graph ?
(2)
7.8.3
When does the reaction reach equilibrium for the first time?
(1)
7.8.4
Explain what has happened to the reaction between t = 8 and
t = 12 minutes
(4)
How will the equilibrium constant, Kc be affected by this disturbance ?
Use INCREASE, DECREASE or STAYS THE SAME.
(2)
7.8.5
42 marks
Page 13 of 15 QUESTION EIGHT
V
Chromium electrode Copper electrode X
Copper (II) sulphate solution Cotton wool
plugs
Chromium (III) sulphate solution Consider the diagram of a copper – chromium Galvanic cell above. The copper electrode is
placed in a copper(II) sulphate solution while the chromium electrode is placed in a solution
of chromium(III)sulphate.
8.2.1
Write down the chemical formula of chromium(III) sulphate
(1)
8.2.2
Define the term oxidation
(1)
8.2.3
Write down the chemical half reactions for the two redox processes that
occur in each half cell.
(2)
8.2.4
Which electrode acts as the anode ? ( write down only Cu or Cr)
(1)
8.2.5
Write down the net ionic equation that occurs in this cell.
(2)
8.2.6
What are the standard electrochemical conditions under which this cell
was set up ?
(2)
8.2.7
Calculate the cell emf under these standard conditions.
(2)
8.2.8
Is the reaction that occurs in this cell spontaneous ? Explain your answer
by referring to your calculation above.
(2)
Page 14 of 15 8.2.9
Consider the component labelled X in the diagram
(a)
Name the component X
(1)
(b)
Suggest a suitable chemical reagent that might
(1)
be used in X
(c)
8.2.10
Give two possible functions of component X
(2)
Write down the cell notation for this Galvanic cell.
(4)
21 marks
QUESTION NINE
Consider the diagram below of an electrolytic cell involving the electrolysis of a concentrated
silver chloride solution
+
-­‐ Power source Graphite
electrodes
AgCl (aq)
9.1
Explain the difference between a Galvanic and an electrolytic cell ?
(2)
9.2
Which electrode would be the cathode in this cell ?
(1)
9.3
What would be observed at the anode when the power source is switched on ?
Write down the half reaction to explain this observation.
(2)
Page 15 of 15 9.4
Calculate the mass of silver deposited if a current of 1,5A is allowed to flow
through the circuit for 2 minutes .
( charge on e- = 1,6 x 10-19C
9.5
9.6
(6)
NA = 6,02 x 1023 )
It is important to ensure that the AgCl solution is concentrated during this
electrolytic process.
9.5.1
What would be observed if a dilute solution of AgCl was used ?
(2)
9.5.2
Write down the half reaction to support this observation.
(2)
The silver chloride solution is now replaced with a concentrated solution of
sodium chloride. Instead of the expected sodium metal being formed, it was
observed that hydrogen gas was seen bubbling at the electrode. Using half
reactions, explain why this has happened.
19 marks
(4)