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F.5 CHEMISTRY
SUMMER ASSIGNMENT
Time allowed: 2 hr 30 minutes
This paper must be answered in English.
Class :_______
1.
2.
3.
Name: ___________________________(
)
Score:
/120
There are TWO sections, A and B, in this paper. Section A carries 36 marks and Section B carries 84
marks. You are advised to finish Section A in about 45 minutes and Section B in about 105 minutes.
Section A consists of multiple-choice questions, while Section B contains conventional questions.
Answers to Section A should be marked on the Multiple-Choice Answer Sheet while answers to Section B
should be written in the spaces provided in Question-Answer Book. The Answer Sheet for Section A and
4.
the Question-Answer Book for Section B must be handed in separately at the end of the
examination.
Part of the Periodic Table and Avogadro constant can be found below.
Periodic Table
Atomic number
Relative atomic mass
Avogadro constant = 6.02 x 1023
F5/ Chemistry/ Summer Assignment/ P. 1
Section A: Multiple-Choice Questions
INSTRUCTIONS
1. ANSWER ALL QUESTIONS.
2.
3.
You should mark only ONE answer for each question. If you mark more than one answer, you will
receive NO MARKS for that question.
All questions carry equal marks. No marks will be deducted for wrong answers.
1. X is an element in the Periodic Table and X+ ion has an electronic arrangement of 2, 8, 8,
A. X is a halogen.
B. X is a transition element.
C. X is a group 0 element.
D. X is a period 4 element.
2. M is an element in the Periodic Table. M2– ion possesses 45 neutrons and 36 electrons. What is M?
A. Se
B. Kr
C. Sr
D. Rb
3. What is the formula of titanium(II) oxide?
A.
B.
C.
D.
TiO
TiO2
Ti2O
Ti2O3
4. Ag+ reacts spontaneously with Ru but not with Pd. Rank the metals in terms of their strength as reducing
agents.
A.
B.
C.
D.
strongest → weakest
Pd > Ag > Ru
Pd > Ru > Ag
Ru > Pd > Ag
Ru > Ag > Pd
5. Which of the following properties is considered the most important one when choosing an alloy for making
fuse in electric plugs?
A. low melting point
B. good ductility
C. high electrical conductivity
D. high mechanical strength
F5/ Chemistry/ Summer Assignment/ P. 2
6. Which of the following hazard warning labels should be displayed on the reagent bottle of methanol?
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
7. Which of the following molecules is the most polar?
A. CHCl3
B. SF6
C. BF3
D. CO2
8. Which one of the following hydrocarbons exhibits geometrical isomerism?
A. CH3CH2CH=CH2
B. (CH3)2C=CHCH3
C. CH3CH=CHCH2CH3
D. CH2=C(CH3)2
9. 0.8 mole of a liquid X was found to contain 19.2 g carbon, 3.2 g hydrogen and 56.8 g chlorine. What is the
molecular formula of X?
A.
B.
C.
D.
CH2Cl
C2H2Cl
C2H4Cl
C2H4Cl2
10. 14.8 g of butan-1-ol (molar mass = 74) were refluxed with sodium bromide and sulphuric acid, after which
17.8 g of 1-bromobutane (molar mass = 137) were collected. What is the percentage yield of this
conversion?
A. 54%
B. 65%
C. 78%
D. 83%
11. Which equation represents an oxidation reduction reaction?
A. HCl + KOH → KCl + H2O
B. 4HCl + MnO2 → MnCl2 + 2 H2O + Cl2
C. 2HCl + CaCO3 → CaCl2 + H2O + CO2
D. 2HCl + FeS → FeCl2 + H2S
F5/ Chemistry/ Summer Assignment/ P. 3
12. Consider the following equation:
6PbO(s) + O2(g)  2Pb3O4(s) ΔHr
H f [PbO(s)] = ΔH1
H f [Pb3O4(s)] = ΔH2
Calculate the standard enthalpy change of the above reaction, ΔHr ?
Given that:
A.
B.
ΔH1  ΔH2
ΔH1 + ΔH2
C.
D.
6ΔH1  2ΔH2
2ΔH2  6ΔH1
13. The graph on the right shows the variation of concentration of a reactant with time as a reaction proceeds.
What is the average reaction rate during the first 20 s?
A. 0.0025 mol dm-3 s–1
B. 0.0050 mol dm-3 s–1
C. 0.0075 mol dm-3 s–1
D. 0.0150 mol dm-3 s–1
Concentration/
mol dm-3
14. The equation for the complete combustion of propane is:
C3H8(g) +
+
2
2(g)
2O(l)
30 cm3 of propane is mixed with 250 cm3 of oxygen and the mixture is ignited.
What is the volume of the resulting gas mixture? (All volumes are measured at the same temperature and
pressure.)
A. 140 cm3
B. 170 cm3
C. 190 cm3
D. 260 cm3
15. What is the name of the compound shown on the right?
A. 5-methylpent-1-en-4-ol
B. 1-methylpent-4-en-2-ol
C. hex-1-en-4-ol
D. hex-5-en-3-ol
F5/ Chemistry/ Summer Assignment/ P. 4
OH
CH2-CH-CH2-CH=CH2
CH3
16. Which of the following changes will cause the equilibrium position to shift to the left?
Ni (s) + 4CO (g)
Ni(CO)4 (l) ΔH° = - 160.8 kJ
A. increasing temperature
B. removing some Ni
C. removing some Ni(CO)4
D. decreasing volume
17. Consider the following chemical equation:
x VO2+(aq) + y H+(aq) + 2 I–(aq) → x VO2+ (aq) + z H2O(l) + I2(aq)
(V is the symbol for the element vanadium.)
Which of the following combinations is correct?
x y z
A. 1 2 1
B. 1
C. 2
D. 3
4 2
4 2
6 3
18. Gas X is bubbled into solution Y as shown below:
Which of the following combinations would give no visible change in the test tube?
A.
B.
C.
D.
X
sulphur dioxide
chlorine
ethene
carbon dioxide
Y
sodium hydroxide solution
sodium iodide solution
acidified potassium permanganate solution
calcium hydroxide solution
19. There are two unlabelled bottles in the laboratory. One of the bottles contains an aqueous solution of
common salt and the other contains antiseptic alcohol. Which of the following methods can be used to
distinguish the substances in the bottles?
(1) adding a small amount of water
(2) detecting their odour
(3) measuring their electrical conductivity
A. (1) and (2) only
B. (1) and (3) only
F5/ Chemistry/ Summer Assignment/ P. 5
C. (2) and (3) only
D. (1), (2) and (3)
20. Consider the redox reaction represented by the equation below:
2 S2O32–(aq) + I2(aq) → S4O62–(aq) + 2 I– (aq)
Which of the following statements is / are correct?
(1) The oxidation number of sulphur in S2O32–(aq) is +3.
(2) One of the half equations of this reaction is 2 S2O32–(aq) → S4O62–(aq) + 2e–.
(3) I2(aq) is oxidized by S2O32–(aq) in the reaction.
A. (1) only
B. (2) only
C. (1) and (3) only
D. (2) and (3) only
21. Which of the following statements concerning a zinc-carbon cell are correct?
(1) Manganese(IV) oxide acts as the anode.
(2) Ammonium chloride acts as an electrolyte.
(3) Zinc acts as the negative electrode.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
22. Using carbon as electrodes, which of the following solutions would give hydrogen upon electrolysis?
(1) 1 M silver nitrate solution
(2) 2 M sodium hydroxide solution
(3) 5 M calcium chloride solution
A. (1) only
B. (2) only
C. (1) and (3) only
D. (2) and (3) only
23. A certain form of solid carbon is composed of C60 molecules. Each C60 molecule is formed by 60 carbon
atoms bonded together like a football as shown in the diagram below:
Which of the following statements is / are correct?
(1) The molar mass of C60 is 12.0 g.
(2) C60 dissolves well in non-polar solvent.
(3) The melting point of the solid is higher than that of diamond.
A. (1) only
B. (2) only
F5/ Chemistry/ Summer Assignment/ P. 6
C. (1) and (3) only
D. (2) and (3) only
24. The polymer formed from the polymerization of 1,1-dichloroethene is commonly used in making food wrap
for microwave cooking. Which of the following can represent a part of the structure of the polymer?
A.
B.
C.
D.
25. Which of the following substances is commonly used to make feeding bottles?
A. Low-density polyethene
B. Polystyrene
C. Expanded polystyrene
D. Polyvinyl chloride
26. Sodium hydroxide reacts with acids. Which of the following solutions would give the highest initial rate?
A. 60 cm3 of 1.5 M NaOH(aq) and 60 cm3 of 1.5 M HCl(aq) at 30C.
B. 20 cm3 of 2.0 M NaOH(aq) and 20 cm3 of 2.0 M HCl(aq) at 30C.
C. 50 cm3 of 2.0 M NaOH(aq) and 50 cm3 of 2.0 M HCl(aq) at 20C.
D. 40 cm3 of 1.5 M NaOH(aq) and 40 cm3 of 2.0 M CH3COOH(aq) at 25C.
27. Compound E rapidly decolourises cold acidified potassium permanganate solution. When E is added to
sodium hydrogencarbonate solution, effervescence occurs. Which of the following compounds may E be?
A.
B.
C.
F5/ Chemistry/ Summer Assignment/ P. 7
D.
28. In the structure of X shown below, certain bond angles are marked.

CH3
H
N(a)
C
CH3
H
C(b)


CH3
C(c)
O
H
CH3
Compound X
Which of the following shows the correct values of bond angles ,  and .

A.
B.
C.
D.

o
180
120o
107o
109o

o
180o
109o
105o
105o
90
120o
120o
120o
29. A student directly poured concentrated sulphuric acid into a sink, which was connected to a catch pot made
of PVC. After sometimes, the catch pot deformed. Which of the following explanations for the deformation
of the catch pot is/ are correct?
(1) Concentrated sulphuric acid oxidized the PVC.
(2) Concentrated sulphuric acid mixed with water to produce large amount of heat to soften and melt PVC.
(3) Concentrated sulphuric acid catalyzed the decomposition of PVC.
A. (1) only
B. (2) only
C. (1) and (3) only
D. (2) and (3) only
30. In an experiment, a copper rod and an iron rod are dipped into dilute sulphuric acid, with their top ends
touching each other. Hydrogen bubbles are found around the copper rod.
iron rod
dilute sulphuric
acid
copper rod
hydrogen
gas bubbles
Which of the following statements about the experiment is correct?
A.
B.
C.
D.
Electrons flow from copper rod to iron rod.
Iron is more reactive than copper.
The iron rod becomes coated with copper.
Copper reacts with the acid.
F5/ Chemistry/ Summer Assignment/ P. 8
31. Which of the following are the functions of porous nickel electrodes in the hydrogen-oxygen fuel cells?
(1) They act as electrical conductors that connect the fuel cell to the external circuit.
(2) They act as catalysts for the reactions.
(3) They increase the surface area for the reactions.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
32. Which of the following statements concerning the electrolysis of concentrated sodium bromide solution
using graphite electrodes are correct?
(1) The main product at the anode is O2(g).
(2) H+(aq) ions are preferentially discharged at the cathode to form H2(g).
(3) The solution becomes sodium hydroxide solution after electrolysis.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
Directions:
Each question below (Questions 33 to 36) consists of two separate statements. Decide whether
each of the two statements is true or false; if both are true, then decide whether or not the second
statement is a correct explanation of the first statement. Then select one option from A to D
according to the following table:
A. Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
B. Both statements are true and the 2nd statement is NOT a correct explanation of the 1st statement.
C. The 1st statement is false but the 2nd statement is true.
D. Both statements are false.
33.
D
1st statement
Carbon dioxide and silicon dioxide have
similar physical properties.
2nd statement
Both carbon dioxide and silicon dioxide have
simple molecular structures.
34.
C
Use of catalyst increases the product yield of
chemical reaction.
Catalyst speeds up both the forward and
backward reaction.
35.
C
For the equilibrium system:
4 HCl(g) + O2(g)
2 Cl2(g) + 2 H2O(g)
An increase in volume of reaction vessel
Kc remains unchanged when the volume of the
reaction vessel is increased.
shifts the equilibrium position to the right.
36.
A
Concentrated sulphuric acid cannot be used
to dry hydrogen bromide gas.
Concentrated sulphuric acid can oxidize
hydrogen bromide to bromine.
~ End of Section A ~
F5/ Chemistry/ Summer Assignment/ P. 9
Class :_______
Name: ___________________________(
)
Section B: Question-Answer Book
Answer ALL questions.
1.
(a) A ship’s hull is made from iron. Blocks of another metal are attached to the hull to prevent the iron from
rusting.
(i) Suggest what this metal might be.
[1 mark]
Zinc/ magnesium [1]
(ii) Explain how the metal named in (a) (i) protects iron from rusting.
[1 mark]
Zn/ Mg is more reactive than iron [0.5] and will be corroded instead of Fe/ will prevent rusting
of iron by sacrificial protection [0.5].
(b) The frames of greenhouses are often made of aluminium. Although they are not painted, they last for
many years.
Aluminium frame
(i)
Explain why aluminium is resistant to corrosion despite its high reactivity.
[2 marks]
Al reacts with oxygen to form aluminium oxide [0.5] which forms a non-porous coating [0.5]
impervious to water and oxygen [1], hence prevent further carrion from taking place.
(ii) Knowing that aluminium is highly abundant in the earth’s crust, a student remarked, “Recycling of
used aluminium objects is economically unsound.”
Do you agree with the student? Explain.
[1 mark]
No. The extraction of Al from its ore involves electrolysis and a huge amount of energy is
required/ aluminium objects do not contain much impurities, cost of removal of impurities is
low [1].
[5 marks]
2. Phosphorus compounds have many uses.
(a) (i)
About 250 000 tonnes of phosphorus trichloride, PCl3, are produced each year. PCl3 is made by
the reaction of phosphorus, P4, with chlorine, Cl2.
The word equation for this reaction is shown below.
phosphorus + chlorine → phosphorus trichloride
Write a balanced chemical equation for this reaction.
P4 + 6 Cl2 → 4 PCl3
F5/ Chemistry/ Summer Assignment/ P. 10
[1 mark]
(ii) Draw the electron diagram of phosphorus trichloride (showing the outermost electron shell only).
[1 mark]
[1]
(iii) Draw a three-dimensional diagram to show the shape of phosphorus trichloride.
[1 mark]
[1]
(b) Phosphorus reacts with zinc to form a compound that is used as a rat poison.
A sample of this compound was found to contain 1.95 g of zinc and 0.62 g of phosphorus.
Calculate the formula of this compound.
[2 marks]
Zn
P
No. of moles:
1.95 / 65.4
0.62/ 31
= 0.0298 = 0.02
Simplest ratio:
3
2
The formula of rat poison is Zn3P2 (s)
[1]
[0.5]
[0.5]
[5 marks]
3.
Consider the formulation of a chromium bath for electroplating given below:
Formulation
CrO3
250 g dm-3
H2SO4
2.5 g dm-3
----------
-----------------
(a) Name one object which is usually plated with chromium.
[1 mark]
Car bumper/ faucet [1]
(b) Before electroplating, the items to be plated are often cleaned by organic cleaning agents. Explain
why it is necessary.
[1 mark]
To remove grease [0.5] which hinders smooth/ firm coating [0.5].
(c) The function of H2SO4 in the bath is to convert CrO3 (s) into chromic acid (H2CrO4).
Complete and balance the half-equation below to show the reaction taking place at the cathode during
electroplating.
[1 mark]
H2CrO4 + ___________
→ _________________________________
+
H2CrO4 + 6 H + 6 e → Cr + 4 H2O [1]
(d) In electroplating industry, the waste solution may further be treated by adding iron powder. Why?
To recover precious metals/ chromium [1]
[1 mark]
F5/ Chemistry/ Summer Assignment/ P. 11
[4. In the 1970s, the effects of pollutants from power stations were being seen in the lakes of Britain and
Scandinavia. The problem was due to sulphur dioxide produced, form acid rain, which contains sulphuric
acid. The problem became so great that in many lakes all the fish died.
In North Wales, the water company treated the acidic lakes with thousands of tones of powdered limestone
(mainly calcium carbonate).
(a) Write chemical equation to show how sulphuric acid can be removed by limestone.
[1 mark]
CaCO3 (s) + H2SO4 (aq) → CaSO4 (s) + CO2 (g) + H2O (l)
(b) If large lumps of limestone are used, most of the limestone would remain unreacted even though the
lake is still acidic. Explain why.
[2 marks]
As the CaSO4 formed is insoluble and forms a protecting coating [1] over the surface of the lumps,
preventing further reaction with the acid [1].
(c) Sodium carbonate solution is alkaline and has a pH of approximately 10. A student suggested using
excess sodium carbonate to remove acidity in acidic lakes. Comment on this suggestion. [1 mark]
Inappropriate as the excess sodium carbonate will dissolve [0.5] and makes the lake water too
alkaline for the survival of aquatic lives [0.5].
(d) Suggest TWO ways to reduce the emission of sulphur dioxide from power stations.
Burn low-sulphur coal [1] and install scrubber [1]
[2 marks]
(e) Other than sulphur dioxide, nitrogen oxides and carbon dioxide are also produced in power stations.
(i)
Describe how nitrogen oxides are formed.
[2 marks]
In the furnance, where the temperature is high [0.5], nitrogen gas in the atmosphere reacts
with oxygen [0.5] to give nitrogen monoxide [0.5]. Nitrogen monoxide further reacts with
oxygen to give nitrogen dioxides [0.5].
(ii)
Explain why the emission of carbon dioxide arouses a great concern though it is harmless.
[1 mark]
Carbon dioxide may lead to global warming.
[9 marks]
5.
Sodium thiosulphate solution reacts with dilute hydrochloric acid according to the following equation.
Na2S2O3 (aq) + 2 HCl (aq) 
 2NaCl (aq) + SO2 (g) + S (s) + H2O (l)
(a)
In order to test for the gas released, a filter paper soaked with acidified dichromate solution is
brought near the reaction mixture.
Write an equation for the reaction involved.
[1 mark]
2+
3+
2Cr2O7 (aq) + 3SO2 (g) + 2H (aq) 2Cr (aq) + 3SO4 (aq) + H2O (l) [1]
(b)
A student proposed to study the effect of concentration of HCl on reaction rate by measuring the
volume of gas released. Explain why this method is NOT appropriate.
[1 mark]
SO2 (g) dissolves well in water [1].
F5/ Chemistry/ Summer Assignment/ P. 12
(c)
Describe an alternative method to study the effect of concentration of HCl on reaction rate for
the reaction.
[9 marks]
In your answer, you are expected to


outline the experimental procedure
give the expected outcome, with explanation in terms of particles.
(Diagrams are NOT required)
For this question, you are required to give answers in paragraph form. 6 of the marks will
be awarded for chemical knowledge and 3 of the marks will be awarded for effective
communication.
Keep a 1M Na2S2O3 and 2M HCl in a water bath at fixed temperature for 5 minutes [0.5].
Transfer a fixed volume [0.5] of 1M Na2S2O3 into a conical flask.
Put the conical flask over a paper with a black “X” mark [0.5].
Transfer fixed volume of 2M HCl [0.5] into Na2S2O3. Start the stop-watch upon mixing.
Observe the “X” through the reaction mixture from above [0.5].
Record the time taken for the “X” to become completely invisible [0.5].
The above procedure is repeated using HCl solutions of different concentration [0.5] while
keeping all other conditions e.g. temperature, volume of solutions, the same [0.5]
The more concentrated the HCl used, the shorter the time taken for the black cross to be masked,
[0.5].
When concentration increases, reactant particles are more crowded [0.5] and collide with one
another more frequently [0.5]. This leads to a higher frequency of effective collisions [0.5],
hence, a faster reaction.
[11 marks]
F5/ Chemistry/ Summer Assignment/ P. 13
6.
(a) The viscosity of engine oil can be improved by the addition of certain medium-chain length polymers.
A portion of the chain of one such polymer is shown below.
On average, the molecules of the medium-chain polymer contain 40 carbon atoms.
(i) Suggest the structure of the monomer.
CH2=CHCH2CH2CH3
[1]
[1 mark]
(ii) How many monomer units are incorporated into the average molecule of the polymer?[1 mark]
40/5 = 8
[1]
(b) Used car engine oil can be recycled for use as a fuel by the processes of distillation and cracking.
(i) Assuming a typical molecule of engine oil has the formula C40H82, suggest an equation for a
cracking reaction that could produce diesel fuel with the formula C16H34 and other hydrocarbons
only.
C40H82 → C16H34 + C24H48 [1]
[1 mark]
(ii) Draw a labeled diagram for the set-up used to crack car engine oil and collect the gaseous
products formed.
[3 marks]
[1 for catalyst; 1 for correct position of heating; 1 for collection of gaseous prodects]
(c) Hithane is a mixture of hydrogen and methane. Explain why hithane is a more desirable fuel than
petrol.
[1 mark]
Compare with petrol, hydrogen and methane burns more completely [0.5] and yields less carbon
monoxide/ unburnt carbon particles [0.5].
[7 marks]
F5/ Chemistry/ Summer Assignment/ P. 14
7.
Nescafé has recently launched a self-heating can of coffee. To heat up the coffee, a button is pressed
which mixes the heating ingredients – a very dilute solution of sodium / potassium hydroxide and calcium
oxide. The can then warms up 210 cm3 of coffee by approximately 40 °C.
(a) Write an equation for the reaction between calcium oxide and water.
CaO + H2O → Ca(OH)2
[1 mark]
(b) The rate of the heating may be controlled by altering the pH of the solution. How would you expect
the rate of heating to vary with pH? Briefly explain your answer.
[1 mark]
As pH decreases, the rate of heating will increase [0.5] because
 the acid present further neutralize Ca(OH)2 to give more heat; or
 the neutralization reaction between CaO and acid is more exothermic than the reaction with
water. [0.5]
(c) By drawing an enthalpy change cycle, calculate the standard molar enthalpy change for the reaction
in (a). Given the standard enthalpies of formation of calcium hydroxide, calcium oxide and water
are –1003, –635 and –286 kJ mol–1 respectively.
[2 marks]
CaO (s) + H2O (l) → Ca(OH)2 (s)
Ca (s) + H2 (g) + O2 (g)
Enthalpy change of reaction = +635 + 286 + (-1003)
[1]
= -82 kJ mol-1
[1]
(d) Assuming that the heat capacity for the coffee is the same as that of water, 4.18 J K–1 g–1, calculate
the minimum mass of calcium oxide needed in the can to warm 210 cm3 of coffee by 40 °C.
[2 marks]
Energy required = 210 x 4.18 x 40 = 35112 J
1 mole of CaO yields 82000 J
No. of moles of CaO required to yield 35112 J = 35112 / 82000 = 0.428
Mass of CaO needed = 0.428 x (40.1+16) g = 24 g
6 marks]
F5/ Chemistry/ Summer Assignment/ P. 15
[1]
[0.5]
[0.5]
8. The following two methods can be used to convert copper metal into copper (II) nitrate solution:
Method 1:
Cu (s)
Method 2:
Cu (s)
CuO (s)
dilute HNO3 (aq)
Cu (NO3)2 (aq)
dilute HNO3 (aq)
Cu (NO3)2 (aq)
(a) Refer to Method 1.
(i) Suggest how copper metal can be converted into copper (II) oxide. State the expected
observation in the reaction that you have suggested.
[2 marks]
Heating copper in air [1]. The brown solid gradually turns black [1].
(ii) Name the type of reaction that occurs between copper (II) oxide and dilute nitric acid.[0.5 mark]
Neutralization [0.5].
(b) In Method 2, copper metal with dilute nitric acid to give a colourless gas.
(i) Name this gas.
Nitrogen monoxide [0.5]
(ii) Write the chemical equation for this reaction.
3Cu (s) + 2NO3¯ (aq) + 8H+ (aq) 3Cu2+ (aq) + 2NO (g) + 4 H2O (l)
[1]
3Cu (s) + 8HNO3 (aq) 3Cu(NO3)2 (aq) + 2NO (g) + 4 H2O (l)
[1]
(c) Which of these methods would you recommend for the conversion of copper metal into
copper (II) nitrate solution? Justify your answer with TWO reasons.
Method 1 because
(1) No toxic nitrogen monoxide is evolved in method 1.
[0.5 mark]
[1 mark]
[2 marks]
(2) More HNO3 is required to produce same amount of Cu(NO3)2 in method 2 than method 1.
9.
In an experiment to determine the concentration of ammonia in a sample of window cleaner, 25.0 cm3 of
the sample was diluted to 250.0 cm3 in a volumetric flask. 25.0 cm3 of the dilute sample was transferred to
a conical flask and was then titrated against 0.23 M sulphuric acid using methyl orange as indicator.
15.8 cm3 of the acid was required to reach end-point.
(a) Predict the colour change at the end-point.
Yellow [0.5] to orange [0.5]
(b) Calculate the molarity of the ammonia in the sample of window cleaner.
[1 mark]
[2 marks]
(You may assume that ammonia is the only substance in the sample that reacts with sulphuric acid.)
H2SO4 + 2NH3 → (NH4)2SO4
No. of moles of H2SO4 = 0.23 x 15.8 / 1000 = 3.634 x 10-3
No. of moles of NH3 present in 25.0 cm3 = 7.260 x 10-3
No. of moles of NH3 present in 250 cm3 = 7.260 x 10-2 (0.0726)
Molarity of NH3= 0.0726/ 0.025 = 2.9072 M
F5/ Chemistry/ Summer Assignment/ P. 16
[0.5]
[0.5]
[0.5]
[0.5]
(c) Arrange the following substances according to their melting points in ascending order. Explain your
answer.
NH3;
NCl3;
NH4Cl
[3 marks]
NH4Cl has giant ionic structure in which ions are held by strong ionic bond [0.5] whereas the other
three exist as simple molecules and are held by weaker [0.5] intermolecular forces [0.5]. NH4Cl thus
has the highest melting point.
NH3 are held by H-bond [0.5] where as NCl3 are held by relatively weaker [0.5] van der Waals forces
[0.5], NCl3 thus has a lower melting point.
Melting point:
NCl3
< NH3<
NH4Cl
[6 marks]
10. The diagram below shows a gas syringe containing a pale brown mixture of N2O4 (g) and NO2 (g) at
equilibrium at room temperature:
N2O4 (g)
colourless
2 NO2 (g)
brown
rubber cap
plunger
A B
a mixture of N2O4 (g) and NO2 (g)
The plunger is quickly pushed from position A to position B at time t1 while the temperature of the mixture
is kept constant.
State the expected observation, with reason(s). Sketch on the given graph to show the expected variation in
the concentration of NO2 (g) in the mixture until the attainment of a new equilibrium.
[3 marks]
Expected observation(s):
Reasons(s):
turns darker brown [0.5], then turns pale [0.5]
As volume decreases, the mixture becomes more concentrated in
N2O4 (g) and NO2 (g) [0.5], therefore turns darker. Decrease in volumes
leads to an increase in pressure. The equilibrium shifts to left to reduce the
Graph:
[NO2 (g)]
[3 marks]
t1
F5/ Chemistry/ Summer Assignment/ P. 17
time
11. Consider the following sequence of reactions for compounds A to C.
HBr (g)
A
( C4H8 )
Step 1
B
( C4H9Br )
NaOH (aq)
C
K2Cr2O7/ H2SO4
Step 2
(C4H10O)
Step 3
no reaction
Deduce the structures of compounds A to C. Give reasons.
[3 marks]
A undergoes addition reaction to give B. A is an alkene/ has C=C bond [0.5].
B undergoes substitution reaction to give C. C is an alcohol [0.5].
C is resistant to oxidation. C is thus a tertiary structure [0.5].
A:
B:
[0.5]
C:
[0.5]
[0.5]
[3 marks]
12. The diagram on the right shows a set-up for preparing
methyl ethanoate from two compounds, A and B.
(a) Write the structural formula of methyl ethanoate.
[1 mark]
(b) Name compounds A and B.
[1 mark]
Ethanoic acid [0.5] and methanol [0.5]
(c) Write an equation for the reaction involved.
Mixture of A and
B with a few
drops of
concentrated
sulphuric acid
(d) State TWO functions of concentrated sulphuric acid in the reaction.
[1 mark]
[1 mark]
As catalyst [0.5]
To remove water so that the equilibrium position lies towards the right, hence , hence improving the
product yield [0.5]
(e) State and explain the function of apparatus X.
To condense the vapour [0.5] and prevent loss of volatile components [0.5]
[5 marks]
F5/ Chemistry/ Summer Assignment/ P. 18
[1 mark]
13. (a) Suggest a synthetic route for the following conversion. For each step, give the reagent(s),
condition(s) and structure of the organic product formed.
[3 marks]
O
CH3CH2
C
CH3CH=CH2
NH2
Step 1: H+ (aq), heat => CH3CH2COOH
Step 2: (i). LiAlH4 in dry ether (ii) H+=> CH3CH2CH2OH [0.5]
Step 3: conc. H2SO4, 180oC
[3 full marks; deduct 0.5 for each missing/ wrong reagent (or structures)]
(b) Ester of 2,3-dibromopropan-1-ol with phosphoric acid are useful flame retardants used in plastics and
fibres.
2,3-dibromopropan-1-ol can be made from propenal by the following two-stages process.
Step 1
Step 2
intermediate A
(i)
Draw the structure of intermediate A.
CH2=CHCH2OH
or
(ii) Suggest reagents and conditions for step 1 and 2 respectively.
Step 1: 1. LiAlH4 in dry ether 2.H+
Step 2: Br2
The steps can be reversed
(iii) 2,3-dibromopropan-1-ol exists as two isomeric forms.
I. Draw diagrams to show the difference between them.
II.
Name a method by which the two forms can be distinguished.
F5/ Chemistry/ Summer Assignment/ P. 19
[1 mark]
[2 marks]
[1 mark]
[1 mark]
14. In the Haber process, ammonia is synthesized by the exothermic reaction of nitrogen and hydrogen at
around 723 K.
N2(g) + 3H2(g)
ΔH° = negative
2NH3(g)
In a simulation of the process, a mixture of nitrogen and hydrogen was placed in a closed container. The
initial concentration of nitrogen and hydrogen were 0.50 mol dm -3and 1.50 mol dm-3 respectively. When
the equilibrium was attained at 723 K, 25.0% of the original nitrogen was consumed.
(a) Calculate the respective concentrations of nitrogen, hydrogen and ammonia in the equilibrium
mixture.
[3 marks]
Ini. Conc.
N2(g)
0.5
+
Change
-0.5 x 0.25
Conc. At eqm 0.375
[1]
3H2(g)
1.5
2NH3(g)
/
-0.5 x 0.25 x 3
1.125
[1]
+0.5 x 0.25 x 2
0.25
[1]
(b) Calculate Kc for the reaction at 723 K.
Kc = (0.25)2/ (0.375)(1.125)3
[0.5]
= 0.117 mol-2dm6
(c) (i)
[1 mark]
[0.5]
State the effect of an increase in temperature on Kc for the reaction.
Kc becomes smaller with an increase in temperature.
[1 mark]
(ii) Explain why the Haber process is not operated at temperatures much higher or much lower than
723 K.
[1 mark]
At a much higher temperature, product yield is low. At a much lower temperature, the rate is
slow.
[6 marks]
~ End of the Paper ~
F5/ Chemistry/ Summer Assignment/ P. 20