Daughters of Mary Help of Christians
Siu Ming Catholic Secondary School
Test on Electrochemical Cell
Form Four Chemistry
Time : 35 minutes
Write down the answers of the following questions on SINGLE-LINE PAPERS
Section A : Multiple Choice
1. In which of the following equations does the
underlined reactant undergo reduction?
A. PbO(s) + CO(g) → Pb(s) + CO2(g)
B. Ca(OH)2(g) + CO2(g)
→ CaCO3(s) + H2O(l)
C. 2H2S(g) + SO2(g) → 3S(s) + 2H2O(l)
D. KClO(aq) + SO2(g) + H2O(l)
→ KCl(aq) + H2SO4(aq)
6. In which of the following compounds does
nitrogen have th HIGHEST oxidation number?
A. N2H4
C. HNO2
B. NO
D. N2O5
7. Sulphur dioxide acts as an oxidising agent in
which of the following reactions?
A. SO2(g) + 2Mg(s) → 2MgO(s) + S(s)
B. SO2(g) + 2KOH(aq) →
K2SO3(aq) + H2O(l)
C. SO2(g) + Cl2(g) + H2O(l) →
H2SO4(aq) + 2HCl(aq)
D. 5SO2(g) + 2KMnO4(aq) + 2H2O(l) →
K2SO4(aq) + 2MnSO4(aq) + 2H2SO4(aq)
2. A simple salt bridge can be made by using the
FILTER paper soaked in a solution of
A. sodium nitrate.
B. hydrochloric acid.
C. potassium hydroxide.
D. glucose.
8. Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)
Which of the following statements about the
above equation is incorrect?
A. Iron(III) oxide is reduced.
B. Carbon monoxide is the reducing agent.
C. Carbon monoxide is reduced.
D. Iron(III) oxide is an oxidising agen.
3. Which of the following is/are true about the
zinc-carbon dry cell?
(1) Zinc is used up as the cell operates.
(2) The cell is rechargeable.
(3) The cell does not deliver a steady
reliable current.
A. (1) only
C. (1) and (3) only
B. (3) only
D. (2) and (3) only
9. The pair of metals which would produce the
largest voltage if used as the electrodes of a
chemical cell is
A. copper and lead.
B. lead and iron.
C. iron and magnesium.
D. magnesium and copper.
4. Which of the following cells is best used in a
digital watch?
A. zinc-carbon cell
B. alkaline manganese cell
C. silver oxide cell
D. nickel-cadmium cell
10. The cathode of a chemical cell is
(1) the positive pole.
(2) the negative pole.
(3) the electrode where oxidation takes
place.
(4) the electrode where reduction takes
place.
A. (1) and (3) only C. (2) and (3) only
B. (1) and (4) only D. (2) and (4) only
5. The action of dilute nitric acid on copper is
represented by the following reaction:
aCu(s) + bHNO3(aq) →
cCu(NO3)2(aq) + dH2O(l) + eNO(g)
The values of a, b, c, d and e in a balanced
equation are
a
b
c
d
e
A.
1
4
1
2
2
B.
3
8
3
4
2
C.
3
4
3
2
2
D.
1
3
1
2
2
Direction: Each question below (Questions 11-12) 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 her
1
2
second statement is a correct explanation of the first statement. Then select one option from A
to D according to the following table:
A.
B.
C.
D.
Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.
The 1st statement is false but the 2nd statement is true.
Both statements are false.
2nd Statement
1st Statement
11.
12.
The electrolyte of zinc-carbon cell is
anhydrous.
Copper is a stronger oxidizing agent than
zinc.
Section B :
Zinc-carbon cell is called dry cell.
Zinc loss electrons more readily than copper.
Structured Questions
1. (a) (i) Give the oxidation state of manganese in each of the following;
(1) MnSO4
(2) MnO2
(3) KMnO4
(ii) For each of the following reactions, explain whether manganese is oxidized or
reduced.
(1) 4KMnO4(aq) + 12HNO3(aq) + 5C(s)
→ 4Mn(NO3)2(aq) + 4KNO3(aq) + 5CO2(g) + 6H2O(l)
−
+
2+
2−
2−
(2) 2Mn (aq ) + 5S 2 O 8 (aq ) + 8H 2 O(l) → 10SO 4 (aq ) + 2MnO 4 (aq ) + 16H (aq )
(3) K2MnO4(aq) + C2H5OH(aq) → K2MnO3 + CH3CHO(aq) + H2O(l)
(6 marks)
(b) (i) What would be observed when dilute sulphuric acid is added to
(1) Iron, followed by warming?
(2) Copper, followed by warming?
(ii) Write equations for any reactions which occur. State the role of sulphuric acid.
(6 marks)
2. (a) The following diagram shows the longitudinal section of a dry cell:
(i) Name the material commonly used to make
(1) rod P, and
(2) case Q.
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(ii) State the oxidising agent.
What is its function in the cell?
Explain with the aid of chemical equations.
(iii) (1) A dry cell often leaks after prolonged use. Explain the cause of leakage based on
the reaction taking place at Q with the aid of chemical equations.
(2) Name one type of cell which is leak-proof.
(9 marks)
2. (b) The apparatus below was used to compare the reactivity of four metal A, B, C and D.
The metal strips were placed in turn onto the moist filter paper as shown:
The results were as follows:
Metal under test
A
B
C
D
Direction of electron flow in
the external circuit
A to Cu
Cu to B
C to Cu
D to Cu
Voltage recorded (V)
+0.8
-2.2
+1.4
+0.3
(i) Why were the metal strips and the copper sheet first cleaned with sand paper?
(ii) Which of these metals is / are less reactive than copper?
Explain your choice.
(iii) With reference to the results, arrange the four metals in order of decreasing reactivity.
(iv) What would happen to the voltmeter reading if the experiment is repeated using a filter
paper soaked in tetrachloromethane? Explain.
(v) Estimate the recorded voltage if A is coupled to C.
(7 marks)
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DMHC Siu Ming Catholic Secondary School
Form Four Chemistry First Term Test 2
Suggested answer
Section A : Multiple choice (40%)
1.
2.
3.
4.
5.
C
A
C
C
B
6.
7.
8.
9.
10.
D
A
C
D
B
11.
12.
C
C
[12× 1]
Section B : Structured question (60%)
1. a)
(i) (1) +2
(2) +4
(3) +7
(ii) (1) Manganate(VII) ion is reduced to Manganese(II) ion.
Decrease in oxidation number
(2) Manganese(II) ion is oxidised to manganate(VII) ion.
Increase in oxidation number.
(3) Mangnate(VI) ion is reduced to manganate(IV) ion.
Decrease in oxidation number.
(1) Iron gradually dissolves to give a green solution.
Hydrogen gas bubbles are given off at metal surface.
(2) No apparant observation/reaction.
(ii) For reaction of iron with acid:
Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)
OR
Fe(s) + 2H+(aq) → Fe2+(aq) + H2(g)
Sulphuric acid acts as an oxidising agent.
b) (i)
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[1]
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[1+1]
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2. (a) (i) (1) graphite / carbon
[1]
(2) Zinc
[1]
(ii) manganese(IV) oxide / manganese dioxide / MnO
[1]
2
It is used to remove (or oxidise) the hydrogen produced
at the graphite electrode (rod P)
[1]
2MnO2(s) + H2(g) → Mn2O3(s) + H2O(l)
[1]
(iii) (1) Zinc metal is oxidised to zinc(II) ion in the outercasing
[1]
[1]
Zn(s) → Zn2+(aq) + 2eThe metal casing becomes thinner in a used dry cell and it leaks eventually.
[1]
(2) Alkaline manganese cell / Silver oxide cell / Nickel cadmium cell
[1]
2 (b) (i) To ensure better electrical conductivity /
To remove oxides or other impurities on the metal surface.
(ii) B
When B is in contact with the filter paper, electrons flow from copper to B,
showing that B is less likely to lose electrons relative to copper.
(iii) C > A > D > B
(iv) The voltmeter reading would be 0V in each case.
Tetrachloromethane, being a covalent solvent (or non-polar liquid),
does not conduct electricity.
(v) 0.6 V
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