C3.21 The electrolysis of aqueous sodium chloride solution
When the electrolysis of aqueous sodium chloride takes place,
hydrogen and chlorine are given off as gases and sodium hydroxide is left.
Aqueous sodium chloride contains hydrogen ions H+ and hydroxide
ions OH- (from the water) and sodium ions Na+ and
chloride ions Cl-. The positive sodium and hydrogen ions go
to the cathode and the negative chloride and hydroxide ions go to the anode.
Hydrogen is formed at the cathode and chlorine is formed at the anode.
| substance | test | result |
| hydrogen | lighted splint | squeaky pop |
| chlorine | damp blue litmus | turns red then white |
| sodium hydroxide | damp red litmus | turns blue/purple |
Task C3.21 Write a word and a balanced chemical equation for the reaction in which hydrogen burns. Complete: Chlorine is (acidic/alkaline) because it turns litmus red. Chlorine is a (dye/bleach) because it turns litmus white. This type of reaction is (oxidation/reduction).
C3.22 Uses of sodium chloride, hydrogen, chlorine and sodium hydroxide
| substance | uses |
| sodium chloride | preserve food, flavouring, stops ice on roads because salt lowers freezing point of water to -5oC, manufacture of sodium, chlorine and sodium hydroxide |
| chlorine | kills bacteria in swimming pools and drinking water, bleach, making hydrochloric acid and solvents. |
| hydrogen | rocket fuel, making margarine, making ammonia |
| sodium hydroxide | detergents, bleach, paper, fibres, purifying bauxite |
Task C3.22 Match the uses above to the explanations below: compounds of carbon and chlorine are good at dissolving grease, hydrogen reacts with chlorine to form hydrogen chloride, vegetable oil reacts with hydrogen to form margarine, nitrogen and hydrogen react together in the Haber process, soap is made from vegetable oil and sodium hydroxide, the structure of wood is broken up by sodium hydroxide, salt is easily detected by the tongue, bacteria cannot survive in salty solutions, by the electrolysis of molten sodium chloride, by the electrolysis of aqueous sodium chloride.