Preparation of chlorine gas

Chlorine gas can be prepared in the laboratory by the oxidation of concentrated hydrochloric acid using oxidising agents such as potassium permanganate, manganese(IV) oxide, and lead(IV) oxide. When manganese(IV) oxide and concentrated hydrochloric acid are used to prepare chlorine, gentle heating is required. The set-up for the laboratory preparation of chlorine gas is show in Figure 1.3. The equation for the chemical reaction that takes place is as follows:

Chlorine gas is passed through water in the first conical flask to remove any acid spray and hydrogen chloride gas. The concentrated sulphuric acid in the second flask is for drying the chlorine gas. Chlorine is denser than air and can be collected over water because it is fairly soluble in water forming yellow chlorine water.

The other methods of preparing chlorine gas are similar to the one illustrated in Figure 1.3. The main difference is the oxidising agent used and the conditions under which the reactions take place (Table 1.3). For instance;

(a) Potassium manganate (VII), is a very strong oxidising agent and when used instead of manganese (IV) oxide, no heating is needed during the reaction.

(b) Mixing manganese(IV) oxide with sodium chloride is another convenient method of preparing chlorine gas. Concentrated sulphuric acid is added instead of concentrated hydrochloric acid and heating is required during this reaction. The mixture reacts to form respective metal salts, water, and chlorine gas. The overall equation for the reaction is as follows:

(C) Chlorine can also be prepared by the action of dilute hydrochloric acid on calcium hypochlorite, Ca(CIO)2 (bleaching powder). No heating is required.

Table 1.3 Summary of the reagents and conditions for preparing chlorine gas