When salts dissolve in water, positive and negative ions that can move through the water molecules are released
Electrolysis can be used, in some cases, to separate these two types of ions
Cathode:
- Copper ions are attracted to the cathode, where they gain electrons to form copper atoms
- The salmon pink discolouration seen at the cathode is a thin layer of copper metal
- \(Cu^{2+}(aq) +2e^- \rightarrow Cu (s) \)
Anode:
- Chloride ions are attracted to the anode, where they lose electrons and combine to form molecules of chlorine gas
- Bubbles can be see at the anode - this is the chlorine gas
- \(2Cl^-(aq) \rightarrow Cl_2(g) +2e^-\)
Note:
- This is not the case for solutions of ionic salts containing more reactive metals such as sodium
- Water also decomposes to form hydrogen and hydroxide ions
- Hydrogen ions gain electrons more easily than sodium and so will be preferentially reduced
- Hydrogen gas will be seen at the cathode
- The reactive metal remains in solution

Electrolysis for AQA Comb