Home / iGCSE Chemistry (0620) Core:7.1 The characteristic properties of acids and bases: Exam Style Questions Paper 1

iGCSE Chemistry (0620) Core:7.1 The characteristic properties of acids and bases: Exam Style Questions Paper 1- New Syllabus

iGCSE Chemistry (0620) Core Paper 1 - All Chapters

Question

A mixture of two substances, R and S, is heated gently.
The damp red litmus paper turns blue.
What are R and S?
▶️ Answer/Explanation
Correct Option: A

Detailed solution:

Damp red litmus paper turning blue indicates the presence of an alkaline gas, which is ammonia (NH₃). Ammonia is produced when a base reacts with an ammonium salt upon heating. Therefore, one substance must be a base (a basic oxide) and the other must be an ammonium salt (ammonium chloride, NH₄Cl). The basic oxide reacts with ammonium chloride to release ammonia gas, which then turns the red litmus paper blue.

Question

A solution containing hydroxide ions, $\text{OH}^-\text{(aq)}$, is added to a solution containing hydrogen ions, $\text{H}^+\text{(aq)}$. An equation representing the reaction is shown.
\[\text{H}^+\text{(aq) + OH}^-\text{(aq) → H}_2\text{O(l)}\]
Which statement about the reaction is correct?
A. The hydrogen ions represent an alkali.
B. The reaction is a neutralisation reaction.
C. The reaction is a reduction.
D. As the $\text{OH}^-$ ions are added, the pH of the reaction mixture falls.
▶️ Answer/Explanation
Correct Option: B

Detailed solution:

This equation shows hydrogen ions (from an acid) reacting with hydroxide ions (from an alkali) to form water. That’s the classic definition of a neutralisation reaction. Hydrogen ions represent an acid, not an alkali. Adding OH⁻ ions neutralises the acid, causing the pH to rise, not fall. It’s not a reduction because no electrons are transferred in this specific neutralisation.

Question

Three compounds are listed.
  1. aluminium nitrate
  2. ammonium chloride
  3. ammonium nitrate
All three compounds are heated with aqueous sodium hydroxide.
Which compounds produce ammonia?
A. 1 and 3
B. 1 only
C. 2 and 3
D. 2 only
▶️ Answer/Explanation
Correct Option: C

Detailed solution:

When a base like sodium hydroxide is heated with an ammonium salt, ammonia gas is produced. Both ammonium chloride and ammonium nitrate contain the ammonium ion ($\text{NH}_4^+$), so they release ammonia. Aluminium nitrate does not contain ammonium ions, so it won’t produce ammonia in this reaction. That means compounds 2 and 3 produce ammonia.

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