An analyst is given four white or coloured solids, A, B, C and D. Each solid is a different salt that dissolves in water. The analyst dissolves each solid in distilled water and carries out four tests.
The table shows the results.
| Salt | Flame test | Add sodium hydroxide solution until in excess | Add dilute nitric acid, then silver nitrate solution | Add dilute hydrochloric acid, then barium chloride solution |
|---|---|---|---|---|
| A | lilac | no precipitate | cream precipitate | no change |
| B | no colour | white precipitate that dissolves in excess | no change | white precipitate |
| C | orange-red | white precipitate that does not dissolve in excess | white precipitate | no change |
| D | blue-green | blue precipitate | no change | white precipitate |
Name salt A and salt C.
Deduce the formula of salt B. Aluminium ions are Al3+\mathrm{Al^{3+}}Al3+.
Write the ionic equation, with state symbols, for the formation of the white precipitate when sodium hydroxide solution is added to a solution of salt B.
A second analyst tests salt D by adding dilute sulfuric acid and then barium chloride solution. She sees a white precipitate and concludes that D contains sulfate ions.
Explain why her method does not show that D contains sulfate ions.
A fifth solid, E, is a mixture of two of the salts A, B, C and D. A solution of E gives these results:
flame test: lilac
sodium hydroxide solution: white precipitate that dissolves in excess
dilute nitric acid, then silver nitrate solution: cream precipitate
dilute hydrochloric acid, then barium chloride solution: white precipitate
Deduce which two salts are in E. Explain how the results support your answer.
Another analyst says that E could instead be a mixture of potassium sulfate and aluminium bromide. Explain whether these four tests can tell the two possible mixtures apart.
35 exam-style questions on Edexcel GCSE Chemistry 10.1 Qualitative analysis: tests for ions, covering 10.1.1 Principles of ion tests and flame tests, 10.1.2 Tests for cations and for ammonia, 10.1.3 Tests for anions, 10.1.4 Identification of ions in unknown salts, and 10.1.5 Instrumental methods of analysis. Each one has a worked solution and a mark scheme showing where the marks go.