Baptist Lui Ming Choi Secondary School
Suggested Answers
SECTION A
1. D A
11. C D
21. A A
31. B A
B
D
C
C
A
C
A
C
Mock Examination (2018-19)
Form 6 Chemistry
D
B
B
C
6.
16.
26.
36.
C
D
B
A
D
A
C
A
B
C
B
B
A
Score: ______/ 120
Date: 29/01/2019
Time: 8:40-11:10 a.m.
C
D
D
SECTION B
1.
a.
b.
The reaction is a redox reaction. Since oxidation number of lithium change from 0 to +1. [1]
i.
[1]
ii.
[1]
iii.
iv.
Two bond pairs and two lone pairs [1]
V-shape [1]
i.
No change [1]. Since zinc is more reactive than iron/ It loses electrons more easily than
iron [1]
Blue colour forms [1]. Since tin is less reactive than iron/ Iron loses electrons more easily
than tin to form iron(II) ion [1]
Iron food cans should be plated with tin. Since tin ion is non-toxic but zinc ion is toxic. [1]
2.
a.
ii.
iii.
b.
i.
Colourless gas bubbles evolve/ magnesium dissolves/ heat is given out [1]
Mg + 2HCl  MgCl2 + H2/ Mg + 2H+  Mg2+ + H2 [1]
ii.
The reaction between magnesium and hydrochloric acid is exothermic/ increases the
temperature [1] and solubility of CO2 in carbonated water decreases as temperature
increases [1].
Electrolysis of molten magnesium oxide (or magnesium chloride). [1]
iii.
P.T.O.
1
3.
a.
b.
iii.
i.
2H+(aq) + OCl-(aq) + Cl-(aq)  Cl2(g) + H2O(l) [1]
(1) Chlorine should not be dried by calcium oxide because they will react. [1+1] OR
Chlorine gas should not be collected by upward delivery, because it is denser than
air. (1+1)
(2) Chorine gas should be dried by anhydrous calcium chloride or concentrated sulphuric
acid. [1] OR
Chlorine gas should be collected by downward delivery (or gas syringe). (1)
Do the experiment in fume cupboard (or a well ventilated room) [1].
NaOH +HNO3  NaNO3 + H2O
[1]
ii.
Set-up [1] & Label any TWO [1]
iii.
iv.
From pink to colourless.[1]
Add dilute nitric acid to 1M sodium hydroxide solution in the same volume ratio as that in
the titration result, without adding the indicator. (or repeat the titration without adding
indicator.) [1]
i.
To produce extra petrol for meeting the demands (or To produce alkenes which can be
used to make other chemicals). [1]
(1) CH3CH2CH=CH2 and but-1-ene [1+1]
or
i.
ii.
4.
a.
ii.
CH3CH=CHCH2 and but-2-ene
or
CH3C(CH3)=CH2 and (2-)methylpropene
Chemical test: 1 + observation: 1 (with comparison)
To Be Continued
2
4.
b.
i.
ii.
To keep the superglue in an air-tight container/ a dry place. [1]
Addition polymerization
[1]
iii.
iv.
[1]
CH2=C(CN)COOH and CH3OH [1+1]
i.
ii.
iii.
iv.
v.
i.
Electrons flow from magnesium to zinc, as magnesium is more reactive than zinc. [1]
Magnesium electrode: oxidation/ losing electrons
[1]
2+
Mg  Mg + 2e [1]
Interchange copper and zinc in cell X. [1]
Voltmeter reading drops to zero. [1]
Experiment 1 because sodium hydroxide solution with high purity can be obtained [1]. or
5.
a.
b.
Experiment 2 because sodium metal is very reactive/ it is very dangerous to carry out
experiment 1/ It is very difficult to control the reaction of experiment 1. (1)
ii.
P.T.O.
3
6.
a.
b.
CH3OH(l) + 3/2O2(g)  CO2(g) + 2H2O(l)
Hc = -715 kJmol-1 [1]
i.
E = m1c1T + m2c2T
[1M]
E = (50x4.2+400x2.1)x33.2
E = 34860J (or 34.86KJ)
[1A]
No. of mole of methanol burnt, n = 1.60/ (12+3+16+1) = 0.05 mol
ii.
c.
Hc = E/ n = 34.68/ 0.05
= -697 kJ mol-1
[1A]
Heat loss to the surroundings/ incomplete combustion of methanol/ the experiment was
not carried out under standard conditions/… (any ONE) [1]
Enthalpy change cycle [1]:
𝐻𝑓𝜃 [CaC𝑂3 (s)]
Ca(s) + C(graphite) +3/2O2(g) →
H1
CaCO3(s)
H2
CaO(s) + CO2(g)
Hf[CaCO3(s)]
Hf[CaCO3(s)]
7.
a.
=
=
=
=
H1 + H2
Hf[CaO(s)] + Hf[CO2(g)] + H2
(-635) + (-394) + (-178)
-1207 kJmol-1 [1A]
[1M]
HCl < HBr < HI < HF [1]
Intermolecular forces between HF molecules are hydrogen bonds as it contains highly
electronegative fluorine atom [1]. Since hydrogen bond is stronger than dipole-dipole
interactions, boiling point of HF is higher than that of other hydrides [1].
Intermolecular forces between HCl, HBr and HI molecules are van der Waals’ forces [1]. Since
molecular size increases from HCl to HBr and then HI, boiling point increases from HCl to HBr
and then HI [1].
*EC =1 (max = 5)
b.
i.
ii.
iii.
Measure volume of CO2 gas produced by using gas syringe over time. [1] or
Measure pressure of CO2 gas produced by using pressure sensor over time. Or
Measure decrease in mass of CO2 gas produced by using electronic balance over time.
Increased temperature increases the speed of reactant particles, hence increases the
number of collisions /collisions with energy greater than or equal to the activation
energy* / effective collisions. [1]
Increased surface area of MgCO3 provides a greater rate of reaction. [1]
To Be Continued
4
7.
b.
iv.
No. of mole of CO2 formed
= no. of mole of MgCO3 reacted
= 1/ (24.3+12+3x16) = 0.01186 mol
Volume of CO2 produced = 0.01186 x 24 = 0.285dm3 [1]
v.
[1]
8.
a.
b.
[𝐶𝑂𝐶𝑙2 (𝑔)]
[𝐶𝑂(𝑔)][𝐶𝑙2 (𝑔)]
= 1.67 mol-1dm3 // [1M+1A]
KC =
ii.
The decomposition of phosgene is endothermic. From the graph, COCl2 concentration
decreases while CO and Cl2 concentrations increase after the temperature increases [1],
showing that the decomposition is endothermic, which is favourable as temperature
increase. [1]
[𝐶𝑂(𝑔)][𝐻2 (𝑔)]3
[𝐶𝐻4 (𝑔)][𝐻2 𝑂(𝑔)]
=
0.2
i.
=
0.3×0.4
0.75 0.75 3
][
]
5
5
2.00 1.25
[
][
]
5
5
[
=
[0.15][0.15]3
[0.4][0.25]
= 5.06x10-3 mol2dm-6 // [1A]
i.
Q=
ii.
iii.
Since Q < KC, hence equilibrium position shifts to R.H.S. [1]
To decrease the pressure: Since there are less gaseous molecules on the LHS than that of
the RHS this will cause the equilibrium to shift to the right. [1]
ii.
Isomer I [1]. Since it has a higher symmetry than isomer II, its molecules are packed more
closely tegether in solid state. [1]
i.
2,3-dibromobutane (or structural formula:
9.
a.
b.
) [1]
P.T.O.
5
b.
ii. 3D structures of optical isomers of 1,3-dibromobutane (with mark “*” at the chiral centre)
[1+1]
c.
i.
ii.
Sodium hydroxide solution (or NaOH(aq)) [1].
Structure of butanedioic acid [1].
iii.
Set-up of refluxing [set-up: 1 + labels (any TWO): 1]
i.
(1) Initial reaction of oxide layer with the acid to give aluminium chloride.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
(2) Initial reaction of oxide layer with the alkali to give aluminate
Al2O3 + 2OH– + 3H2O → 2[Al(OH)4]–
Metal reacts with the acid/ alkali/ water and then hydrogen gas is evolved.
2Al + 6HCl → 2AlCl3 + 3H2
2Al + 6H2O → 2Al(OH)3 + 3H2
2Al + 6OH– + 6H2O → 2[Al(OH)6] 3– + 3H2
2ClO-(aq)  2Cl-(aq) + O2(g)
[1]
10.
a.
ii.
b.
i.
ii.
[1]
(1)
[1]
(1)
[1]
(1)
(1)
(1)
Co(OH)2(s) reduces ClO- to Cl- and itself is oxidized to Co(OH)3(s) in the presence of water
[1].
6