Ionic substances in solution break down into elements during electrolysis. Different elements are released depending on the particular ionic substance.
At the negative electrode
At the negative electrode, positively charged ions gain electrons. This is reduction, and you say that the ions have been reduced.
Metal ions and hydrogen ions are positively charged. Whether you get the metal or hydrogen during electrolysis depends on the position of the metal in the reactivity series:
- The metal will be produced if it is less reactive than hydrogen
- Hydrogen will be produced if the metal is more reactive than hydrogen
So the electrolysis of copper chloride solution produces copper at the negative electrode. But the electrolysis of sodium chloride solution produces hydrogen.
At the positive electrode
At the positive electrode, negatively charged ions lose electrons. This is oxidation, and you say that the ions have been oxidised. The table summarises some of the elements you should expect to get during electrolysis.
| Negative ion in solution | Element given off at positive electrode |
|---|---|
| Chloride, Cl– | Chlorine, Cl2 |
| Bromide, Br– | Bromine, Br2 |
| Iodide, I– | Iodine, I2 |
| Sulfate, SO42– | Oxygen, O2 |
Putting it together
The table shows some common ionic compounds, and the elements released when their solutions are electrolysed.
| Ionic substance in solution | Element at the negative electrode | Element at the positive electrode |
|---|---|---|
| Copper chloride, CuCl2 | Copper | Chlorine |
| Copper sulfate, CuSO4 | Copper | Oxygen |
| Sodium chloride, NaCl | Hydrogen | Chlorine |
| Hydrochloric acid, HCl | Hydrogen | Chlorine |
| Sulfuric acid, H2SO4 | Hydrogen | Oxygen |
Posted on 07:54 / 1
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