FORM 5 CHEMISTRY TIME: 1h 45min · PDF file · 2016-09-274 Sodium bromide (NaBr)...
Transcript of FORM 5 CHEMISTRY TIME: 1h 45min · PDF file · 2016-09-274 Sodium bromide (NaBr)...
Chemistry – Form 5 Secondary – Track 2 – 2016 Page 1 of 12
DIRECTORATE FOR QUALITY AND STANDARDS IN EDUCATION
Department of Curriculum Management
Educational Assessment Unit
Annual Examinations for Secondary Schools 2016
FORM 5 CHEMISTRY TIME: 1h 45min
Name: _________________________ Class: _______________
Useful Data Atomic numbers and relative atomic masses are shown in the periodic table printed below.
One mole of any gas occupies 22.4 dm3 at standard temperature (0 °C / 273 K) and
pressure (1 atm. / 760 mmHg).
Faraday constant = 96500 C mol-1
Q = It
PERIODIC TABLE
1 2 3 4 5 6 7 0
1
1H
4
2He
7
3Li
9
4Be
11
5B
12
6C
14
7N
16
8O
19
9F
20
10Ne
23
11Na
24
12
Mg
27
13Al
28
14Si
31
15P
32
16S
5.35
17Cl
40
18Ar
39
19K
40
20Ca
45
21Sc
48
22Ti
51
23V
52
24Cr
55
25Mn
56
26Fe
59
27Co
59
28Ni
5.63
29Cu
65
30Zn
70
31Ga
73
32Ge
75
33As
79
34Se
80
35Br
84
36Kr
85
37Rb
88
38Sr
89
39Y
91
40Zr
93
41Nb
96
42Mo
99
43Tc
101
44Ru
103
45Rh
106
46Pd
108
47
Ag 112
48Cd
115
49In
119
50Sn
122
51Sb
128
52Te
23
11Na
127
53I
23
11Na
131
54Xe
133
55Cs
223
87Fr
137
56Ba
139
57La
178
72Hf
181
73Ta
184
74W
186
75Re
190
76O s
192
77Ir
195
78Pt
197
79Au
201
80
Hg 204
81Tl
207
82Pb
209
83Bi
210
84Po
210
85At
222
86Rn
Key: a
bX
relative atomic mass
symbol atomic number
Marks Grid [ For Examiner’s use only ]
Question
No.
Section A Section B
1 2 3 4 5 6 7 8 9
Max
Mark 10 10 10 10 10 10 20 20 20
Theory
Total
Actual
Mark
Theory Paper: 85% Practical: 15% Final Score: 100%
Track 2
Page 2 of 12 Chemistry – Form 5 Secondary – Track 2 – 2016
SECTION A – Answer ALL questions. This section carries 60 marks.
1 Earth’s atmosphere is made up of a mixture of gases.
a) Name the two most abundant gases in Earth’s atmosphere.
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b) Give the percentage amount for each of the gases mentioned above.
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c) Describe, in terms of the kinetic theory of matter, the behaviour of particles in a gas.
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d) Carbon dioxide is a gas that is found in Earth’s atmosphere. Draw a dot cross
diagram of a molecule of carbon dioxide showing outer shells only.
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e) What is the name of the type of bond present in carbon dioxide?
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f) A component of the Earth’s atmosphere is made of elements that do not form
molecules. Name one of these elements.
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g) Name the process by which the gases present in air can be separated from each other.
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Chemistry – Form 5 Secondary – Track 2 – 2016 Page 3 of 12
2 Sea water is a solution of many salts dissolved in water. The main salt present in sea
water is sodium chloride, NaCl. When sea water evaporates, crystals of NaCl form.
a) In humid conditions NaCl crystals absorb water vapour from the air and dissolve to
form a concentrated solution. What is the name of this process?
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b) Sea water is not suitable to drink. Describe how fresh water can be obtained from sea
water by reverse osmosis.
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c) The graph below shows the solubility of sodium chloride against temperature.
i) How much NaCl, in grams, is required to produce a saturated solution at 90 °C
if 1000 g of water are used? ________________________________________
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ii) What would happen if a saturated solution at 90 °C is allowed to cool to room
temperature?
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d) Draw a dot cross diagram of sodium chloride.
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Solu
bil
ity –
gra
m N
aCl
100 g
H20
Temperature (°C)
Page 4 of 12 Chemistry – Form 5 Secondary – Track 2 – 2016
3 Acids are a group of substances that have similar chemical properties. They react with
many materials and are corrosive. Hydrochloric acid is an example of a mineral acid.
a) For each of the materials below, write a balanced chemical equation to show what
happens when the material and hydrochloric acid are mixed together.
i) calcium oxide
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ii) sodium carbonate
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b) When acids react with metals such as magnesium, hydrogen gas is generated. Draw a
diagram of the apparatus in the space provided below, to show how hydrogen gas can
be produced and collected in the lab.
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c) Describe how hydrogen gas can be tested and state the expected result for this test.
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d) Most crops prefer soil conditions that are not too acidic. A farmer needs to have his
field checked before he plants it. He needs it to be at a pH of around 7.
i) What would you do to check that the soil has an acceptable pH value?
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ii) If the above test shows that the field is too acidic, what should the farmer do to
neutralise the acidity in the soil?
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Chemistry – Form 5 Secondary – Track 2 – 2016 Page 5 of 12
4 Sodium bromide (NaBr) is a salt that does not conduct electricity when it is in the solid
state. However, it conducts electricity either when molten or when dissolved in water.
a) Explain why NaBr does not conduct electricity when it is in the solid state.
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If NaBr is in the liquid state, it will conduct a current of electricity and decompose. The
diagram below shows the setup that would be used.
b) Name the substance formed at the cathode.
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c) Write the half equation that happens at the anode.
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The electrolysis of NaBr is a redox reaction.
d) In the electrolytic cell, does oxidation happen at the cathode or the anode?
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e) Explain, in terms of electrons, what happens at the cathode.
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When NaBr is dissolved in water to make a very dilute solution, it will also conduct a
current of electricity.
f) Name the substance formed at the anode, giving a reason for your answer.
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g) Write the half equation that happens at the cathode.
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Page 6 of 12 Chemistry – Form 5 Secondary – Track 2 – 2016
5 During an experiment to identify two white crystalline substances, a student noted the
following observations:
a) When substance A was heated in a blue Bunsen flame, using a nichrome wire, a lilac
colour was observed.
When a sample of substance A was dissolved in distilled water and mixed with
acidified silver nitrate solution a cream precipitate was formed. On mixing another
sample of substance A with lead(II) nitrate, a canary yellow precipitate formed.
Substance A is: ________________________________________________________
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b) When a solution of substance B was mixed with a solution of sodium hydroxide, a
white precipitate was obtained. A flame test gave a brick red colour.
When dilute hydrochloric acid was added to a sample of substance B, a gas that
smells of burning sulfur was produced. Furthermore, a solution of substance B
decolorizes aqueous potassium permanganate.
Substance B is: ________________________________________________________
2
During another experiment to determine the concentration of a solution of sodium
hydroxide, another student decided to perform a titration.
c) The diagrams show two items of the equipment needed to perform a titration. Label
the diagrams in the spaces provided.
1
d) 25 cm3 of sulfuric acid solution whose concentration was 1 mol dm
-3 was used to
neutralise the alkali.
i) Write a balanced chemical equation for the reaction that happens between
sulfuric acid and sodium hydroxide. Do not include state symbols.
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ii) After performing the titration, the average titre value of sodium hydroxide was
found to be 20.5 cm3. Calculate the concentration of this solution.
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Chemistry – Form 5 Secondary – Track 2 – 2016 Page 7 of 12
6 The laboratory preparation of ammonia involves mixing and heating two solid substances,
ammonium chloride and calcium hydroxide.
a) Write a balanced chemical equation including state symbols for this reaction.
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b) The following diagram is a typical setup that is used in the laboratory for the
preparation of ammonia.
i) The diagram shows ammonia being collected in a particular way. What is the
name of this technique?
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ii) Why is ammonia collected in this manner?
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iii) The drying agent used is calcium oxide. Can any drying agent be used to dry
ammonia? Explain your reasoning.
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c) Provided that 5 g of ammonium chloride reacted with excess calcium hydroxide,
calculate the volume of ammonia, in dm3, that would be produced at STP.
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Page 8 of 12 Chemistry – Form 5 Secondary – Track 2 – 2016
SECTION B – Answer TWO questions only. This section carries 40 marks.
7 Ethanol can be obtained either naturally or synthetically.
a) Provided that the molecular formula of ethanol is C2H5OH, draw the display formula
of ethanol showing all bonds.
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b) What is the name of the homologous series which ethanol is a member of?
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1
c) The general formula for alkanes is CnH2n+2. Write the general formula of the
homologous series mentioned in b).
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1
d) Give the name of another member of this homologous series mentioned in b) which
has 4 carbon atoms.
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Ethanol is a basic material in all alcoholic drinks where it is produced naturally. 93% of
the world’s ethanol is produced by this natural process.
e) What is the name of the natural process that produces ethanol?
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f) Describe briefly how this natural process can be performed in a laboratory and label
the apparatus shown below.
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Chemistry – Form 5 Secondary – Track 2 – 2016 Page 9 of 12
7% of the world’s ethanol production is produced synthetically. It is an important
substance because it has many uses.
g) Apart from the use in alcoholic drinks, mention two uses of ethanol.
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h) Complete the following balanced chemical equation including state symbols for the
synthetic production of ethanol.
C _ H _ ( _ ) + H2O( _ ) ⇌ C _ H _ OH(g) 3
The synthetic production of ethanol is a chemical process which reaches equilibrium.
Phosphoric acid, a temperature of 300 °C and a pressure of 60 atmospheres are used to
increase the yield of ethanol.
i) What is the function of phosphoric acid and why is it used?
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j) What does the phrase “increase the yield of ethanol” mean?
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k) Explain why a pressure of 60 atm. is required to increase the yield of ethanol.
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Please turn overleaf.
Page 10 of 12 Chemistry – Form 5 Secondary – Track 2 – 2016
8 During an experiment to investigate the effect of surface area on the rate of chemical
reactions of heterogeneous reactions, a student decided to react calcium carbonate
granules with hydrochloric acid. The following table shows the data of the student’s
experiment.
Time / min 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Volume of CO2 / cm3 0 15 24 28 31 33 35 35 35
a) On the graph below, plot the volume of CO2 against time and label it X.
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b) At which point in time would you say that the reaction came to an end?
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c) When was the rate of reaction at its highest value?
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d) From your graph or otherwise, determine:
i) the time at which the volume of CO2 reached 33 cm3.
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ii) the volume of CO2 that was collected at 1.0 minutes.
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e) What is a heterogeneous reaction?
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f) Complete the following chemical equation, including state symbols, and balance it.
CaCO _ (s) + _ HCl( _ ) ⟶ CaCl _ ( _ ) + H2O( _ ) + CO2(g) 3
Chemistry – Form 5 Secondary – Track 2 – 2016 Page 11 of 12
g) If the reagent bottle holding the acid was to be placed in a refrigerator, its temperature
would be lowered from 20 °C to 4 °C. Given that everything else remained the same,
draw a sketch labelled Y, on the graph plotted in a), to show the rate curve you would
expect.
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h) Explain how changing the temperature of the acid affects the rate of the chemical
reaction.
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The student repeated the original experiment with the same amount of calcium carbonate
and hydrochloric acid. But this time round, the student crushed the calcium carbonate
granules into smaller pieces.
i) On your graph plotted in a), draw a sketch labelled Z, to show the graph expected
when the surface area of the calcium carbonate changes.
1
j) Explain how changing the surface area of calcium carbonate affects the rate of the
chemical reaction.
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9 The Haber process was invented in 1905 by Fritz Haber to solve
the problem of the lack of reactivity of nitrogen. The process
involves reacting nitrogen and hydrogen to form ammonia in
liquid form. Ammonia is mainly used in the production of
fertilizers and explosives.
a) Why do you think that nitrogen is so unreactive?
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b) Complete and balance the following chemical equation, including state symbols, for
the production of ammonia by the Haber process.
N2( _ ) + _ H2( _ ) ⇌ _ NH _ ( _ ) 3
Page 12 of 12 Chemistry – Form 5 Secondary – Track 2 – 2016
c) This process is one that requires special conditions. List these conditions with respect
to:
the catalyst used - ______________________,
temperature - _________________________,
and pressure - ________________________.
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d) Would the use of a catalyst produce more ammonia? Explain.
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e) What would happen to the amount of ammonia produced if the pressure on the system
increases? Explain.
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f) Apart from using temperature or pressure to change the equilibrium, what can be
done to increase the production of ammonia? Explain.
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g) Compare the rate of reaction of the forward and backward reactions when this system
is in equilibrium.
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h) 100 cm3 of ammonia gas were stored at STP. Calculate the volume this gas would
occupy if the conditions were changed to a temperature of 38 °C and a pressure of 0.8
atmospheres.
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