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S4 Chemistry: Ion Tests, Flame Tests and Precipitation (Paper 1: Basics)
S4 Chemistry: Ion Tests, Flame Tests and Precipitation (Paper 1: Basics)
Ten items building the basics of flame tests, hydroxide precipitates and the tests for carbonate, sulphate, chloride and ammonium ions.
Direct answers Answers in order: golden yellow, lilac, blue precipitate, green and reddish-brown, ammonia turns red litmus blue, limewater turns milky, white barium sulphate, white silver chloride, 0.0025 mol, 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)
- FoundationWhat colour is seen in the flame test for a sodium compound?
- FoundationWhat colour is seen in the flame test for a potassium compound?
- FoundationWhat colour precipitate forms when sodium hydroxide solution is added to copper(II) ions?
- IntermediateHow do the precipitates differ when sodium hydroxide is added to iron(II) and to iron(III) ions?
- IntermediateWhat gas is released when an ammonium salt is warmed with sodium hydroxide solution, and how is it tested?
- IntermediateWhat is observed when a carbonate is treated with dilute hydrochloric acid, and how is the gas confirmed?
- ChallengeHow do you test a solution for sulphate ions? Give the reagents and the observation.
- ChallengeHow do you test a solution for chloride ions?
- ChallengeHow many moles of silver ions are in 25.0 cm3 of 0.10 mol dm-3 silver nitrate solution?
- Error redoCan a flame test be used to identify anions in solution?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Golden yellow | Sodium ions are excited in the flame and emit golden yellow light, which makes sodium easy to identify. |
| 2 | Lilac (pale purple) | Potassium gives a lilac flame, usually viewed through blue cobalt glass to screen out any sodium yellow. |
| 3 | A blue precipitate | Copper(II) ions react with hydroxide ions to give a blue copper(II) hydroxide precipitate. |
| 4 | Iron(II) gives a green precipitate and iron(III) gives a reddish-brown precipitate. | The two oxidation states give hydroxides of clearly different colours, which allows them to be told apart. |
| 5 | Ammonia is released, and damp red litmus paper turns blue. | Ammonium ions react with hydroxide ions on warming to give ammonia, an alkaline gas that turns damp red litmus blue. |
| 6 | Bubbles of gas are given off and the gas turns limewater milky. | A carbonate with acid releases carbon dioxide, which turns calcium hydroxide solution milky. |
| 7 | Acidify with dilute hydrochloric acid, then add barium chloride solution: a white precipitate insoluble in dilute acid forms. | Sulphate ions give a white barium sulphate precipitate, and acidifying first removes interfering ions such as carbonate. |
| 8 | Acidify with dilute nitric acid, add silver nitrate solution: a white precipitate forms that dissolves in ammonia solution. | Silver chloride is a white precipitate that dissolves in dilute ammonia, which separates it from bromide and iodide. |
| 9 | 0.0025 mol | Moles equal concentration times volume: 0.10 times 0.0250 dm3 gives 0.0025 mol. |
| 10 | No, a flame test identifies metal cations only. | The flame colour comes from electron transitions in metal ions, so anions give no characteristic flame colour. |
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.
Write the reagent and the observation for each item before checking the answer.Tutor Registration →
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