Chemistry > Testing Salts: Anions and Cations
The chart below may help identify the cations and anions in various salt solutions.
Anions
| Anion |
Test and result |
| Bromide (Br-) |
Add a few drops of dilute nitric acid (0.4 ml dm-3 - Irritant) and then a few drops of silver nitrate solution (0.1 mol dm-3). A pale yellow precipitate of silver bromide forms which is slightly soluble in ammonia solution (2 mol dm-3). |
| Chloride (Cl-) |
Add a few drops of dilute nitric acid (0.4 ml dm-3 - Irritant) and then a few drops of silver nitrate solution (0.1 mol dm-3). A white precipitate of silver chloride forms which is soluble in ammonia solution (2 mol dm-3). |
| Iodide (I-) |
Add a few drops of dilute nitric acid (0.4 ml dm-3 - Irritant) and then a few drops of silver nitrate solution (0.1 mol dm -3). A yellow precipitate of silver iodide forms which is insoluble in ammonia solution (2 mol dm-3). |
| Sulfate (SO42-) |
Add a few drops of barium chloride solution (0.1 mol dm-3 – Toxic) and then a few drops of dilute hydrochloric acid (0.4 mol dm-3). A white precipitate of barium sulfate forms. |
| Carbonate (CO32-) |
Add dilute hydrochloric acid (0.4 mol dm-3) to the solution (or solid). Carbon dioxide bubbles are given off. |
Cations
| Cation |
Test and result |
| Ammonium (NH4+(aq)) |
Add sodium hydroxide solution (0.4 mol dm-3 – Irritant). Warm carefully. DO not allow to spit. Ammonia gas is given off. |
| Copper (Cu2+(aq)) |
Add sodium hydroxide solution (0.4 mol dm-3 – Irritant). Blue precipitate of Cu(OH)2(s) forms.
or
Add ammonia solution (2 mol dm-3). Blue jelly-like precipitate dissolves in excess ammonia to form a deep blue solution. |
| Aluminium (Al3+(aq)) |
Add sodium hydroxide solution (0.4 mol dm-3 – Irritant). A colourless precipitate of Al(OH)3(s) forms.
or
Add ammonia solution (2 mol dm-3). A colourless precipitate of Al(OH)3(s) forms |
| Zinc (Zn2+(aq)) |
Add sodium hydroxide solution (0.4 mol dm-3 – Irritant). A white precipitate of Zn(OH)2(s) forms.
or
Add ammonia solution (2 mol dm-3). A white precipitate, Zn(OH)2(s) dissolves in excess NH3(aq) |
| Lead(II) (Pb2+(aq)) |
Add sodium hydroxide solution (0.4 mol dm-3 – Irritant). A white precipitate Pb(OH)2(s) dissolves in excess NaOH(aq).
or
Add ammonia solution (2 mol dm-3). A white precipitate Pb(OH)2 forms. |
| Iron(III) (Fe3+(aq)) |
Add sodium hydroxide solution (0.4 mol dm-3 – Irritant). A rusty coloured precipitate Fe(OH)3(s) forms.
or
Add ammonia solution (2 mol dm-3). A rusty coloured jelly-like precipitate forms. |
| Iron(II) (Fe2+(aq)) |
Add sodium hydroxide solution (0.4 mol dm-3 – Irritant). A green jelly-like precipitate of Fe(OH)2(s) forms.
or
Add ammonia solution (2 mol dm-3). A green jelly-like precipitate forms. |
Important Notes
- Wear eye protection.
- Ammonia solution causes burns and gives off ammonia vapour which irritates eyes, lungs and respiratory system.
- Hydrochloric acid can cause burns.
- Barium chloride is harmful by inhalation and if swallowed.
- Nitric acid causes burns.
- Sodium hydroxide can cause burns and is dangerous of the eyes.
- Silver nitrate solution causes burns.
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