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When a solution of copper (II) sulphate is electrolysed using copper electrodes the following reactions occur:
At the cathode:
Copper ions become copper atoms:
The copper atoms deposit themselves on the cathode.
At the anode:
The copper anode dissolves, forming copper ions:
mass of copper lost at anode = mass of copper gained at cathode
This method is used to purify copper in industry. By placing the impure copper at the anode, pure copper is formed at the cathode, as the copper ions migrate from the impure copper anode.
You can use electrolysis to coat one metal with another. This is called electroplating. Electroplating is used a great deal in industry, for example; chrome-plating car bumpers.
If you wanted to coat a nickel vase with silver, you would set the vase as the cathode and the silver as the anode.
At the anode: Silver dissolves forming silver ions.
At the cathode: Silver ions receive electrons and form a layer of silver on the vase.
The electrolysis of salt water:
This industry has been based around the electrolysis of brine, salty water!
At the cathode: Hydrogen bubbles off:
At the anode: Chlorine bubbles off:
Na+ and OH- ions are left behind, which means a solution of sodium hydroxide forms.
The products from the electrolysis of brine are:
- sodium hydroxide.
These products are used for many purposes:
Sodium hydroxide is used for making, soaps, detergents and paper.
Chlorine is used for making, PVC, solvents, bleach, drugs, hydrochloric acid , paints and dyes.
Hydrogen is used for making fuel for rockets and nylon.