A technician tests rinse water from a chemical process. The rinse water contains one of the following metal ions: aluminium ions, calcium ions or magnesium ions.
The technician adds sodium hydroxide solution to equal volumes of the rinse water in two test tubes. Test tube B had previously contained a solution of magnesium ions and had been emptied but not washed.
| Test tube | Observation after adding a few drops of sodium hydroxide solution | Observation after adding excess sodium hydroxide solution |
|---|---|---|
| A | A white precipitate forms | The precipitate dissolves |
| B | A white precipitate forms | Some white precipitate remains |
Explain how the observations in test tube A identify the metal ion in the rinse water.
Explain the observations in test tube B and predict the incorrect conclusion the technician could make if only test tube B were used.
93 exam-style questions on AQA GCSE Chemistry 8.3 Identification of ions by chemical and spectroscopic means, covering 8.3.1 Flame tests, 8.3.2 Metal hydroxides, 8.3.3 Carbonates, 8.3.4 Halides, 8.3.5 Sulfates, 8.3.6 Instrumental methods, and 8.3.7 Flame emission spectroscopy. Each one has a worked solution and a mark scheme showing where the marks go.