What are the products of electrolysis?
When compounds are electrolysed, new substances are produced at the electrodes. For example, when electricity is passed through molten sodium chloride, pale green chlorine gas comes off at the anode, and shiny molten sodium forms at the cathode.
- Apparatus that helps to investigate the products at the electrodes when aqueous solutions are electrolysed
- Products formed at the electrodes when various liquids and aqueous solutions are electrolysed
- Which types of elements are produced at the anode? Which types of elements are produced at the cathode?
Apparatus that helps to investigate the products at the electrodes when aqueous solutions are electrolysed
The apparatus in Figure 1 helps to investigate the products at the electrodes when aqueous solutions are electrolysed. When copper sulfate solution is electrolysed using this apparatus, a pink deposit of copper appears on the cathode. Bubbles of a colourless gas stream off at the anode and collect in the inverted test tube. This gas relights a glowing splint, showing that it is oxygen.
Products formed at the electrodes when various liquids and aqueous solutions are electrolysed
Table 1 also lists the products formed at the electrodes when various other liquids and aqueous solutions are electrolysed. Note that the products may come from the water when aqueous solutions are electrolysed.
| Substance electrolysed | Product at anode | Product at cathode |
|---|---|---|
| molten sodium chloride | pale green chlorine gas | sodium |
| molten lead bromide | orange-brown bromine gas | lead |
| aqueous potassium iodide | iodine which colours the solution brown | hydrogen |
| aqueous copper sulfate | oxygen | copper (deposited on the cathode) |
| dilute hydrochloric acid | chlorine | hydrogen |
| dilute sulfuric acid | oxygen | hydrogen |
| aqueous zinc bromide | bromine which colours the solution brown | zinc (deposited on the cathode) |
| aqueous sodium chloride | chlorine | hydrogen |
are electrolysed
Which types of elements are produced at the anode? Which types of elements are produced at the cathode?
When acids and ionic (metal/non-metal) compounds conduct electricity, new substances are formed as follows.
– a metal or hydrogen is formed at the cathode.
– a non-metal (except hydrogen) is formed at the anode.
When acids and ionic (metal/non-metal) compounds are electrolytes, the compounds are decomposed by electrical energy. An element is produced at each electrode. This is very different from metals, which are not decomposed when they conduct electricity.
The first two electrolysis in Table 1 can be summarised in word equations as:
