This document discusses reagents used to test for cations and identifies several common cations that can be tested for. Sodium hydroxide and ammonia solutions are used as they contain hydroxide ions, which will react with most metal ions to form precipitates of insoluble metal hydroxides. The cation can then be identified based on the color and solubility of the precipitate, with the document listing sodium, potassium, calcium, aluminium, lead, zinc, iron(II), iron(III), copper(II) and ammonium as some common cations that can be identified.

1. TESTING FOR CATIONS Reagents used are: 1. aqueous sodium hydroxide and 2. ammonia solution are used. Note: Both reagents contain hydroxide ions (OH - ) in solution.

2. Explanation: 1.When in solution, most metal ions will react with hydroxide ions to form precipitates (ppt) 2.T he ppt is actually the insoluble metal hydroxide. 3. The cation can be identified from: - the colour of the precipitate (ppt) - solubility of the ppt in excess alkali.

3. CATIONS TO BE IDENTIFIED Sodium Na + , Potassium K + calcium Ca 2+ aluminium Al 3+ , lead Pb 2+ , zinc Zn 2+ iron(II) Fe 2+ , iron(III) Fe 3+ copper(II) Cu 2+ ammonium NH 4 +