Topic 7.1.3: Reactions of Ammonium Salts
Cambridge IGCSE Chemistry 0620 · Papers 2 & 4 · 15 Questions · 30 Marks
Section A: The Reaction
5 questions · 12 marks
Write the word equation for the reaction between calcium hydroxide and ammonium chloride.
Write the balanced chemical equation, including state symbols, for the reaction between calcium hydroxide and ammonium chloride when heated.
Name the three products formed when calcium hydroxide reacts with ammonium chloride.
This reaction is described as a base reacting with an ammonium salt. Identify the base and the ammonium salt in the reaction between calcium hydroxide and ammonium chloride.
Describe, at the ionic level, what happens to the ammonium ion (NH₄⁺) during this reaction.
Section B: Conditions & Tests
5 questions · 7 marks
What condition is required for a base to react with an ammonium salt?
Describe the test for ammonia gas and state the result that confirms its presence.
Apart from the litmus test, describe ONE other observable property of ammonia gas that helps identify it.
A student performs the ammonia test incorrectly and uses DRY red litmus paper instead of damp paper. What result would they observe?
Write an ionic equation to show why ammonia solution is alkaline.
Section C: Agricultural Context
5 questions · 12 marks
Explain why farmers should NOT add calcium hydroxide (lime) and ammonium nitrate fertilizers to soil at the same time.
Farmers sometimes add calcium hydroxide (lime) to acidic soils. Explain why lime is added and identify what type of chemical reaction occurs.
A farmer uses ammonium sulfate as a nitrogen fertilizer. He plans to add lime (calcium hydroxide) the following week. What advice should be given?
Write a balanced equation for the reaction between calcium hydroxide and ammonium nitrate, a common fertilizer, when heated.
A student heats a white solid with calcium hydroxide. A gas is produced that turns damp red litmus paper blue. (a) Name the gas produced. (b) What does this tell you about the identity of the white solid? (c) Name a specific compound that could be the white solid.
🔑 Core Knowledge Summary
The Key Reaction:
Ca(OH)₂(s) + 2NH₄Cl(s) → CaCl₂(s) + 2H₂O(l) + 2NH₃(g)
Conditions:
Must be HEATED. Base + ammonium salt → salt + water + ammonia
Ammonia Test:
DAMP RED litmus paper → turns BLUE. (All three words must appear in your answer)
Agricultural Warning:
Never mix lime + ammonium fertilizer → NH₃ escapes → nitrogen LOST from soil
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