Chloride

A mixture of manganese (IV) oxide and common salt (sodium chloride) is put into flask. Other apparatuses are fitted as shown in the figure below. Concentrated sulphuric acid is poured down the funnel. When the mixture is heated a greenish yellow gas evolved.

$2NaCl_{(s)} + 2H_2SO_{4(l)} + MnO_{2(s)} \rightarrow NaSO_{4(aq)} + 2H_2O_{(l)} + Cl_{2(g)}$

The impure gas is passed through the first wash bottle which contains water. This removes hydrogen chloride vapour. The second wash bottles contain concentrated sulphuric acid which dries the gas. Being denser than air and soluble in water, chlorine is collected by the downward delivery method. You can also prepare chlorine from hydrochloric acid and manganese (IV) oxide.

When a gas jar of chlorine is inverted over a gas jar of hydrogen sulphide a yellow deposit of Sulphur is formed. Chlorine has oxidized the hydrogen sulphide to Sulphur while itself reduced to hydrogen chloride.

$Cl_{2(g)} + H_2S_{(g)} \rightarrow 2HCl_{(g)} + S_{(s)}$

When chlorine gas is bubbled through a pale green solution of iron (II) chloride, the colour of the solution changes to yellow. Chlorine oxidizes the iron (II) chloride to iron (III) chloride.

$2FeCl_{2(aq)} + Cl_{2(g)} \rightarrow 2FeCl_{3(aq)}$

$2Fe^{2+}_{(aq)} + 4e^- \rightarrow 2Fe^{3+}_{(aq)} + 6Cl^-$

Chlorine displaces bromine and iodine from their aqueous compounds. This is because it is more electronegative and has a greater oxidizing power than the other two.

$2KBr_{(aq)} + Cl_{2(g)} \rightarrow 2KCl_{(aq)} + Br_{2(l)}$

When chlorine gas is bubbled through a colourless solution of potassium bromide, the clear solution immediately turns red due to the formation of bromine water. Finally of a red liquid (bromine) form at the bottom of the test tube. Chlorine has displaced bromine from the potassium bromide.

$2KBr_{(aq)} + Cl_{2(g)} \rightarrow 2KCl_{(aq)} + Br_{2(l)}$

When the experiment is repeated with potassium iodide, the clear solution turns brown. Finally black solid iodine crystal are deposited at the bottom of the test tube. Chlorine has displaced iodine from the potassium iodide.

$2KI_{(aq)} + Cl_{2(g)} \rightarrow 2KCl_{(aq)} + I_{2(s)}$

Chlorine is the bleaching agent. It removes colouring matter from wet papers, clothes, flowers and other plant materials. The gas dissolves and reacts with water to form a mixture of hydrochloric and hypochlorous acid.

$Cl_{2(g)} + H_2O_{(l)} \rightarrow HCl_{(aq)} + HOCl_{(aq)}$

The hypochlorous acid then oxidizes the dye to form a colorless compound.

$HOCl_{(aq)} + \text{Dye} \rightarrow HCl_{(g)} + (\text{Dye} + O)$

The material is to be washed with plenty of water to remove the hydrochloric acid when a damp cloth and paper are separately dropped into gas jars A and B of chlorine, they are immediately bleached. The dry piece of cloth and paper remain unattacked by chlorine. This shows that water is necessary for the formation of hypochlorous acid which is responsible for bleaching. No bleaching occurs if water is absent.

1. Chlorine is used as a bleaching agent and in the manufacturing of other agents. It is used in industries to bleach textiles and wood pulp for making paper.
2. It is used in treatment of water, plants and swimming pools also in killing of germs. Examples of germs it kills are typhoid, dysentery and cholera.
3. It is used in manufacturing of important chemicals such as hydrochloric acid chloroform and carbon tetrachloride.
4. It is used in manufacturing of PVC plastic, e.g. pipes.