A laboratory adds sodium hydroxide solution to separate portions of two wastewater samples, P and Q. The observations are recorded in the table.
| Sample | Observation just after adding sodium hydroxide | Observation after 10 minutes |
|---|---|---|
| P | Blue precipitate | Blue precipitate |
| Q | Green precipitate | Orange-brown colour develops at the surface of the precipitate |
Identify the metal ion in each sample.
Explain why the appearance of the precipitate from Q changes.
107 exam-style questions on OCR GCSE Chemistry 4.2 Identifying the products of chemical reactions, covering 4.2.1 Tests to identify gases, 4.2.2 Tests for aqueous ions and flame tests, and 4.2.3 Instrumental methods of analysis. Each one has a worked solution and a mark scheme showing where the marks go.