AQA A-Level Chemistry AS Paper 1, June 2025: Question 17
1 mark · Easy difficulty · Multiple Choice
Identify which silver halide(s) react with concentrated ammonia solution to form a colourless solution.
Practise this questionQuestion
Question text
17 Which silver halide(s) react(s) with concentrated ammonia solution to form a
colourless solution?
[1 mark]
A silver chloride only
B silver chloride and silver bromide
C silver bromide and silver iodide
D silver iodide only
Mark scheme
Show the mark scheme
17 B 1 (AO1) silver chloride and silver bromide
How to answer it
Solubility of Silver Halides in Ammonia
This question assesses knowledge of Group 7 (halide ion) qualitative tests, specifically the differential solubility of silver halide precipitates (AgCl, AgBr, AgI) in dilute and concentrated aqueous ammonia solution.
- Recalling the solubility trends of silver halides in ammonia.
- Distinguishing between behaviour in dilute versus concentrated NH₃(aq).
- Identifying the complex ion formed when silver halides dissolve ( [Ag(NH₃)₂]⁺ ).
Question 17 Analysis
Multiple Choice: Halide Confirmatory Test
✅ Correct Answer
B: silver chloride and silver bromide
Both AgCl and AgBr dissolve in concentrated aqueous ammonia to form the colourless diamminesilver(I) complex ion:
AgX(s) + 2NH₃(aq) → [Ag(NH₃)₂]⁺(aq) + X⁻(aq)
Because AgCl dissolves even in dilute ammonia, it also readily dissolves in concentrated ammonia. AgBr requires concentrated ammonia to dissolve.
💡 Key Knowledge
Because the colours of AgCl (white), AgBr (cream), and AgI (yellow) can be hard to differentiate by eye, aqueous ammonia is used as a confirmatory test:
| Silver Halide | Dilute NH₃(aq) | Conc. NH₃(aq) |
|---|---|---|
| AgCl (white) | Dissolves | Dissolves |
| AgBr (cream) | Insoluble | Dissolves |
| AgI (yellow) | Insoluble | Insoluble |
Silver iodide is completely insoluble even in concentrated NH₃ because its ionic lattice is too strong relative to the hydration and complexation enthalpy.
❌ Common Errors & Pitfalls
- Selecting Option A (AgCl only): Candidates often confuse the condition in the question (concentrated ammonia) with dilute ammonia. Silver chloride is the only one that dissolves in dilute NH₃.
- Assuming AgCl does not dissolve in concentrated NH₃: A false assumption that if something dissolves in dilute, it somehow reacts differently or fails to dissolve in concentrated ammonia. If it dissolves in dilute, it will definitely dissolve in concentrated!
- Thinking AgI dissolves in concentrated NH₃ (Option C): Forgetting that AgI does not dissolve in ammonia at any concentration.
🧠 Exam Technique & Examiner Insight
- Highlight key conditions: Always underline whether the question states dilute or concentrated ammonia.
- Use a 2-step mental checklist:
1. Does AgCl dissolve in conc. NH₃? Yes (it dissolves in dilute too).
2. Does AgBr dissolve in conc. NH₃? Yes.
3. Does AgI dissolve in conc. NH₃? No.
Conclusion: AgCl and AgBr (Option B). - Formula knowledge: In written papers, examiners frequently ask for the formula of the dissolved complex ion: [Ag(NH₃)₂]⁺ (linear geometry, silver oxidation state +1).
Topics
Inorganic Chemistry · 3.2.3 Group 7(17), The Halogens
Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.