Page 53 - ACE YR IGCSE A TOP APPROACH TO CHEM

(iii) Magnesium, zinc, lead, copper [1] (g) A regular arrangement [1]
of positive ions [1]
(iv) 1.60 V [1]
2.23 V – 0.63 V = 1.60 V and a sea of electrons [1]
9 (a) Zinc is more reactive. [1]
It loses electrons more readily to form zinc 10 Chemistry of the Environment
ions. [1]
Zinc ions react with oxygen and water instead Part 1: Multiple-choice Questions
of iron. [1] 1 B
Iron does not oxidise. [1] The burning of hydrocarbons produces carbon dioxide.
(b) (i) Oxidising agent [1] In a car engine, the temperature is high. Nitrogen and
(ii) Reducing agent [1] oxygen react to form nitrogen dioxide. Hydrocarbons
may contain sulfur. The burning of hydrocarbons
(iii) Iron(III) / Fe [1] containing sulfur produces sulfur dioxide.
3+
2+
(iv) Iron(II) / Fe [1] 2 D
10 (a) Aluminium oxide is dissolved in molten Sulfur dioxide can only be removed through
cryolite. [1] desulfurisation by using limestone.
Cryolite lowers the melting temperature. [1] 3 D
Molten aluminium forms. [1] N – Nitrogen
Anode: P – Phosphorus
K – Potassium
2O ➞ O + 4e [1]
2–
2 4 A
Cathode: Filtration is used to remove the particles. Chlorination is
Al + 3e ➞ Al [1] used to kill bacteria.
3+
(b) Carbon [1] 5 D
reacts with oxygen [1] Gas X is sulfur dioxide. Treating sulfur dioxide with
(c) Any one from: calcium carbonate is called desulfurisation.
Gas Y is carbon monoxide. In a catalytic converter,
Use: Manufacturing aircrafts [1] carbon monoxide reacts with oxygen to form carbon
Reason: Low density / Light [1] dioxide which is less harmful.
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Or
Gas Z is methane. Methane is a greenhouse gas.

Use: Food container [1]
Reason: Resistant to corrosion [1] 6 B
In combustion, oxygen is needed.
(d) (i) 2Al + Fe O ➞ 2Fe + Al O [1] Example: CH + 2O ➞ CO + 2H O
2
3
3
2
2
2
2
4
(ii) Molten iron runs into the cracks and In rusting, oxygen is needed. 4Fe + 3O ➞ 2Fe O 3
2
2
gaps, [1] In extracting aluminium, oxygen is being removed.
and harden [1] 7 B
During photosynthesis, plants take in carbon dioxide and
11 (a) Al O [1] release oxygen.
2
3
(b) Decreases the melting point of alumina [1] During respiration, the lungs take in oxygen.
Alumina melts at 2045°C. Burning needs oxygen. In combustion, a hydrocarbon
Increases the conductivity [1] reacts with oxygen. Therefore, this is the oxidation of
As a solvent / save cost [1] hydrocarbon.
(c) Al + 3e ➞ Al [1] 8 D
3+
There is 21% of oxygen in the air. The amount of oxygen

2O ➞ O + 4e [1]
2–
3
2 is 31.5 cm . Dry air is 100%.
(d) Carbon reacts with oxygen [1] 100 3
Carbon electrodes get eaten away through the Amount of dry air = 21 × 31.5 cm
oxidation of carbon. = 150 cm 3
to form carbon dioxide [1] 9 A
Nitrogen gas is not an air pollutant. Carbon dioxide only
(e) (i) A good conductor of electricity [1] becomes harmful when its concentration is high in the
(ii) Strong [1] air.
Strong steel prevents overhead cables from Carbon monoxide, nitrogen oxide and sulfur dioxide are
sagging. air pollutants.
(f) Any one from: [1] 10 C
• Save energy Desulfurisation is a process for the removal of sulfur
• Reduce carbon dioxide emissions dioxide, but not nitrogen dioxide.
Answers 165

Answers.indd 165 3/4/22 3:54 PM