Page 41 - ACE YR IGCSE A TOP APPROACH TO CHEM

7 A (c) (i)
Increasing the concentration of reactants increases the
particles per unit volume. The particles collide more
frequently. or
8 B
The forward reaction is endothermic. Increasing
the temperature favours the endothermic reaction. [1]
Therefore, increasing the temperature increases the
yield of products. (ii)
9 D
Oxidation = gaining oxygen, losing electrons, increase in Volume of gas / cm 3
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oxidation number
Reduction = losing oxygen, gaining electrons, decrease in
oxidation number Time / s
[1]
2Mg(s) + O (g) ➞ 2Mg O (s)
2–
2+
2 (iii) The flask is heated:
Oxidation number: 0 –2 More particles have enough energy to
The oxidation number decreases from 0 to –2.
react. [1]
10 A Collision rate increases. [1]
Reduction is a process that shows a decrease in oxidation More successful collisions / The energy
number. gained is greater than the activation
H + O ➞ H O energy. [1]
2 2 2 2
Oxidation number: 0 –1
11 D
The sum of the oxidation numbers in an ion is the same
as the charge on the ion.

Part 2: Structured Questions

1 (a) Carbon dioxide escapes from the flask. [1]
Carbon dioxide is a gas. It will escape through the Powdered calcium carbonate is used:
cotton wool. More particles are exposed for the reaction.
[1]
(b) (i) Mass of flask Collision rate increases. [1]
and contents / g
More successful collisions / The energy
gained is greater than the activation
energy. [1]
T 2 cm 1 cm
Time / s
2 cm
At the end of the line when the line stays 1 cm
stagnant. [1]
2 cm 1 cm
(ii) Mass of flask Surface area Surface area
and contents / g = 6 × (2 × 2) cm 2 = 8 × (6 × (1 × 1)) cm 2
= 24 cm 2 = 48 cm 2
2 (a) Measure the initial weight. [1]
Measure the final weight at the end of the
Time / s reaction. [1]
Its weight is unchanged. [1]
Above the original line [1] (b) The line is above the original line. [1]
Ends at the original line [1] Stop at the same volume of gas collected. [1]
When the concentration of the reactant
decreases by half, the rate of reaction (c) The rate of reaction decreases. [1]
decreases by half too. So, the mass of flask and Less surface area available for the reaction. [1]
its contents decreases slower. Collision rate decreases. [1]
But the amount of products formed does not
change. So, the line will end at the same line. (d) Use a glowing splint [1]
Relit the splint [1]

Answers 153

Answers.indd 153 3/4/22 3:54 PM