A student tests a solution for sulfate ions. She adds dilute sulfuric acid to the solution and then adds barium chloride solution. A white precipitate forms.
Which is the best evaluation of her method?
Valid, because the acid removes carbonate ions that would also give a white precipitate
Valid, because the white precipitate can only be barium sulfate from the sample
Not valid, because the acid itself adds sulfate ions, so a precipitate forms anyway
Not valid, because the acid must be added after the barium chloride, not before
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.