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S4 Chemistry: Ion Tests, Flame Tests and Precipitation (Paper 4: Misconception Drill)
S4 Chemistry: Ion Tests, Flame Tests and Precipitation (Paper 4: Misconception Drill)
Ten items targeting the commonest ion test misconceptions about flame colours, precipitate colours and which acid to use.
Direct answers Answers in order: no, it is green, no, warming is needed, no, yes, volatile chlorides form, 0.015 mol, it dissolves to deep blue, no.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S4 Chemistry: Ion Tests, Flame Tests and Precipitation |
| Level | S4 |
02 Questions (10 items)
- FoundationCan a flame test identify an anion?
- FoundationIs the precipitate from iron(II) ions with sodium hydroxide reddish-brown?
- FoundationCan dilute sulphuric acid be used to acidify before testing for sulphate ions?
- IntermediateIs warming unnecessary when testing ammonium ions with sodium hydroxide?
- IntermediateDoes a carbonate release carbon dioxide when sodium hydroxide solution is added?
- IntermediateDoes silver chloride dissolve in dilute ammonia solution?
- ChallengeWhy is the wire moistened with concentrated hydrochloric acid before a flame test?
- ChallengeWhat is the minimum number of moles of hydroxide ions needed to precipitate 0.005 mol of aluminium ions completely?
- ChallengeWhat happens when copper(II) hydroxide precipitate is treated with excess ammonia solution?
- Error redoDo all metal ions give a precipitate with sodium hydroxide?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | No, the flame colour reports the metal ion only. | The characteristic colour comes from electron transitions in metal ions and says nothing about anions. |
| 2 | No, it is green; the reddish-brown precipitate comes from iron(III). | The two oxidation states give differently coloured hydroxides, and mixing them up ruins the identification. |
| 3 | No, it would introduce sulphate ions and give a false positive. | Acidifying only removes interferences, so the acid used must not contain the ion being tested for. |
| 4 | Warming is needed; without it too little ammonia escapes. | At room temperature very little ammonia is released, so the litmus change is unreliable. |
| 5 | No, an acid is needed to release carbon dioxide from a carbonate. | Hydroxide is not an acid and does not react with carbonate to give a gas. |
| 6 | Yes, silver chloride dissolves in dilute ammonia. | This difference in solubility is the key to telling chloride, bromide and iodide apart. |
| 7 | It forms volatile metal chlorides that give a clearer colour and also cleans the wire. | Chlorides vaporise more readily, so the characteristic colour appears clearly in the flame. |
| 8 | 0.015 mol | Each aluminium ion needs three hydroxide ions, so 0.005 times 3 gives 0.015 mol. |
| 9 | The precipitate dissolves to give a deep blue solution. | Copper ions form a deep blue complex with ammonia, which is another characteristic test. |
| 10 | No, sodium and potassium ions do not give a precipitate. | Sodium and potassium hydroxides are soluble, so their solutions show no precipitate with sodium hydroxide. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Turn every wrong item today into one sentence: I thought this, but actually that.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.