A rack of tubes, a shelf of reagents. Name the ions.
Every 9701 Paper 3 ends with a qualitative analysis question, and the marks go to precise observations. By hand, pour each unknown into a clean tube, carry a dropper over it and squeeze a few drops, look, then hold the bulb for excess. Warm tubes in the water bath and hold damp red litmus paper or limewater at the mouth to test gases. The bench shows what happens; you write it down in exam wording, identify the ions and devise a test of your own. The unknowns change every attempt. Allow about 35 minutes.
Past-paper referenceOriginal experiment, wording and numbers, written in the style of Cambridge AS & A Level Chemistry 9701 Paper 3 (Advanced Practical Skills), Question 3. It is not copied from a past paper.This type of experiment has come up 45 times in the past papers we checked. Show the list
Checked: Cambridge 9701 Paper 3, February/March 2023 to May/June 2026. Only the papers in our collection are listed, so the real number may be higher. Question papers are available from Cambridge.
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How this question is marked
Observations (a)
One mark for each box of the results table. Your answer is compared with what actually happened in your own tube, so a test you never finished (no excess added, or no look after the first few drops) cannot score.
Identifying the ions (b)
One mark for each of the four ions: the right ion, and a test that really shows it. Test 1 alone cannot tell magnesium from calcium, for example, so it needs both tests.
Devising a test (c)
A test that gives different results for the two possible ions, the observation you actually made with FA 9, and a conclusion that follows from it.
Exam wording
Colour plus “ppt”, what happens in excess (soluble or insoluble, and the colour of the solution formed), effervescence, and a gas test with its result.
Habits that save marks
A few drops first, then excess: pour in excess at once and you never see the precipitate that dissolves.
Acidify with nitric acid, not hydrochloric acid, before silver nitrate: hydrochloric acid brings its own chloride ions.
A gas needs its test and result: “turns damp red litmus paper blue”, not just “ammonia”.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.