A student tests a white solid and concludes that it is pure potassium sulfate. Her results are:
| Test | Result |
|---|---|
| flame test | lilac flame |
| excess dilute hydrochloric acid added | effervescence; the gas turns limewater milky |
| barium chloride solution then added | white precipitate |
Which is the best evaluation of her conclusion?
Not supported: carbonate ions are also present, so it is not pure potassium sulfate
Supported: the precipitate confirms sulfate ions and the flame confirms potassium
Not supported: the precipitate was barium carbonate, so no sulfate ions are present
Supported: the gas formed when the acid reacted with the sulfate ions present
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.