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CIE iGCSE Co-Ordinated Science C4.2 Hydrogen–oxygen fuel cells Exam Style Questions Paper 2

CIE iGCSE Co-Ordinated Science Paper 2 - All Chapters

Question

X is an oxide. When solid X is added to dilute hydrochloric acid, the pH of the solution increases.
When solid X is added to aqueous sodium hydroxide, the pH of the solution decreases.

Which type of oxide is X?

A. acidic
B. amphoteric
C. basic
D. neutral

▶️ Answer/Explanation
A rise in pH when X is added to hydrochloric acid shows X is neutralising the acid, which is basic behaviour.
A fall in pH when X is added to sodium hydroxide shows X is neutralising the base, which is acidic behaviour.
An oxide reacting with both an acid and a base like this is described as amphoteric.
✅ Answer: (B)

Question

Zinc oxide is an insoluble base. It reacts with dilute hydrochloric acid to produce zinc chloride. Zinc chloride is soluble in water.

Which statement about the preparation of zinc chloride crystals is correct?

A. Once the reaction is complete there is no need to filter the reaction mixture.
B. The reaction mixture is neutral at the point that no more zinc oxide reacts.
C. Zinc chloride crystals are obtained by evaporation to dryness.
D. Zinc chloride precipitates when the solution becomes neutral.

▶️ Answer/Explanation
Zinc oxide, a base, keeps reacting with the acid until no more will dissolve, and at that point the mixture is neutral.
Excess unreacted zinc oxide must still be filtered off (ruling out A), since zinc chloride itself is soluble and stays dissolved, not precipitated (ruling out D).
Crystals are obtained by gently evaporating some water and letting the solution cool, not by evaporating fully to dryness, which would just give a powder (ruling out C).
✅ Answer: (B)

Question

Three methods for investigating rates of reaction are listed.

  1. Observe a colour change.
  2. Use a gas syringe.
  3. Use a balance.

The equation for the reaction of magnesium and dilute hydrochloric acid is shown.

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

Which of the methods can be used to investigate the rate of this reaction?

A. 2 only
B. 1 and 2
C. 1 and 3
D. 2 and 3

▶️ Answer/Explanation
This reaction produces hydrogen gas but involves no colour change, so method 1 (observing a colour change) cannot be used.
A gas syringe can track the volume of hydrogen gas collected over time, giving a direct measure of reaction progress.
A balance can track the loss in mass of the flask as hydrogen gas escapes, giving an equally valid measure.
✅ Answer: (D)
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