The Blast Furnace
Purification of Copper
Crude Oil
Analysing Gases
Haber Process
Solubility of Salts
Test for Anions
Test for Cations

Other Section



Electrolysis of Brine

Brine is merely sodium chloride (NaCl) dissolved in water.

If you perform electrolysis on brine you will get three substances: chlorine, hydrogen and sodium hydroxide.

diagram showing the electrolysis of brine

The cations move towards the cathode. So H+ and Na+ will go this way. The hydrogen gas bubbles up and is collected in the test tube. Pairs of H+ ions will from H2 molecules.

The anions move towards the anode. Cl- is collected in the test tube - it becomes Cl2 molecules, OH - also moves in this direction.

When the current is stopped the Na+ and OH- have no force holding them to their respective electrodes, so they will form ionic bonds together, making sodium hydroxide (NaOH).


To test for hydrogen you first take the test tube, then seal it. Now you get a wooden splint or match and light it. Quickly unseal the test tube and drop the splint in. You should hear a 'pop' sound as the hydrogen combusts in a rapidly exothermic reaction.

To test for chlorine you do the same as with hydrogen, but instead of a match, you drop a damp piece of litmus paper into the test tube. It should turn white because the chlorine has bleached it.

Sodium hydroxide is an alkaline solution so you can use one of the tests you know for that. Turning litmus paper purple or universal indicator turns the solution blue.


This electrolysis process is very useful in the world of industry because the products have alot of uses, as well as the combinations of some of the products as well. The table below outlines some of the products that rely on the electrolysis of brine.

Chlorine:PVC, pesticides; water treatment
Hydrogen:Fuel, margarine
Sodium hydroxide:Soaps and detergents, paper, food products
Sodium chlorate.Soduim hydroxide and chlorine are reacted together to form this which is used in household bleach.