Choose a chemical test, inspect the result, then decide which ions are present. You get a different soluble salt each time. The tests follow AQA and Edexcel GCSE Separate Chemistry.
Flame tests help identify certain metal ions. Sodium hydroxide gives characteristic precipitates with some others. A white hydroxide precipitate on its own is inconclusive: aluminium, calcium and (for AQA) magnesium can give one. Excess sodium hydroxide dissolves the aluminium precipitate.
Carbonate ions release carbon dioxide when dilute acid is added. Confirm the gas using limewater. Sulfate ions produce a white precipitate with barium chloride after acidifying with dilute hydrochloric acid. For halides, acidify with dilute nitric acid, then add silver nitrate: chloride gives white, bromide cream and iodide yellow.
Edexcel also specifies ammonium ions. Warming an ammonium salt with sodium hydroxide produces ammonia; the gas turns damp red litmus paper blue. The AQA ion-identification list does not include ammonium.
Worked example
You see a white precipitate after adding a few drops of sodium hydroxide. That alone does not distinguish all the possible cations. Add excess reagent to a fresh prepared portion of the same test mixture: if the precipitate dissolves, aluminium ions are supported. If it remains, you need more evidence to distinguish the other candidates.
Specification references
AQA 8462, sections 4.8.3.1–4.8.3.5 and required practical 7. Edexcel 1CH0, sections 9.1C–9.7C and core practical 9.6C. See the AQA specification and Edexcel specification.
Investigate an unknown salt
The sample contains one soluble ionic compound. You have clean solid for a flame test and separate portions of its solution for other tests. Each chemical test uses a fresh portion unless stated otherwise.
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Observations
What does your evidence show?
Only the ions listed for the chosen course are considered. A test can be useful without immediately identifying an ion.
Safety and limits
This is a simulation, not a laboratory method sheet. In school, use eye protection, avoid skin contact with chemicals and handle flames, hot solutions and barium salts only under supervision. The virtual tests use idealised observations for single soluble salts. Impurities, mixed ions, concentrations and interfering reactions can make real samples more complicated.
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Practise explaining the tests
Exams also ask you to write methods, give precise observations and explain why a result can be misleading. Write your answer first, then compare it with the points to look for. These are original revision questions, not official exam-board mark schemes.
Check your answer
Select each point you included in your own words.
Example answer:
This is a self-check, not automatic examination marking. Scientifically equivalent wording can also be correct.
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