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2020 O Level Chem P1 Q22 — Ammonia / Reactions of Ammonium Salts Solution

Ammonia / Reactions of Ammonium Salts 2020 O Level Pure Chemistry · Paper 1 · Q22

Question

Ammonia can be displaced from its salts. Which equation is correct?

ACa(OH)₂(s) + NH₄Cl(s) →heat→ CaCl(s) + NH₃(g) + H₂O(g)
BCa(OH)₂(s) + (NH₄)₂SO₄(s) →heat→ CaSO₄(s) + 2NH₃(g) + 2H₂O(g)
CNaOH(s) + 2NH₄NO₃(s) →heat→ NaNO₃(s) + 2NH₃(g) + H₂O(g)
DNaOH(s) + (NH₄)₂SO₄(s) →heat→ NaSO₄(s) + 2NH₃(g) + 2H₂O(g)

Correct answer: B

Video Solution

Explanation

Answer: B (\(\text{Ca(OH)}_2 + \text{(NH}_4)_2\text{SO}_4 \to \text{CaSO}_4 + 2\text{NH}_3 + 2\text{H}_2\text{O}\)). Heating a base such as calcium hydroxide with an ammonium salt displaces ammonia gas. Checking equation B, every element balances: 1 Ca, 1 S, 2 N, 6 O and 10 H on each side, so it is correct.

Option A is wrong because it writes calcium chloride as CaCl, when calcium is +2 so the formula must be CaCl₂, and the equation does not balance. Option C does not balance — there are 4 nitrogen atoms on the left but only 3 on the right. Option D contains the impossible formula NaSO₄; since sodium is +1, sodium sulfate must be Na₂SO₄.

Only option B has correct formulae and balances fully, so the answer is B.

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