Identifying Metal Ions by Precipitation
Higher Tier
Using NaOH solution to identify metal ions
- Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide solution, NaOH (aq)
- A few drops of NaOH is added at first and any colour changes or precipitates formed are noted
Identification of metal ions by addition of NaOH (aq)
The addition of sodium hydroxide to the metal ions forms precipitates of different colours
- A summary of the reactions is shown in the table below
Table showing the colour of the precipitates formed
| Metal ion | Reaction | Colour |
| Fe2+ | Fe2+ (aq) + 2OH– (aq) → Fe(OH)2 (s) | Pale green precipitate |
| Fe3+ | Fe3+ (aq) + 3OH– (aq) → Fe(OH)3 (s) | Orange / brown precipitate |
| Cu2+ | Cu2+ (aq) + 2OH– (aq) → Cu(OH)2 (s) | Blue precipitate |
Exam Tip
You will only have to give state symbols in your answer if specifically asked to.
