Bleaching powder

Bleaching powder is very useful chemical compound which is used extensively for bleaching of clothes. It chemical formula is CaOCl₂ and its chemical name is calcium oxychloride.

Manufacture of Bleaching Powder

Bleaching powder in manufactured by passing chlorine gas over dry slaked lime.

Bleaching powder can be manufactured by using two different types of manufacturing plants.

1. Hasenclever plant and

1. Bachmann plant.

But we will discuss only the manufacturing of bleaching powder by using Hasenclever plant.

Construction of Hasenclever Plant

The Hasenclever plant consists of a number of hollow horizontal cylinders of iron which are fitted with shafts having a large number of blades fixed along entire length which can be rotated inside the cylinders. The uppermost cylinder has a hopper for putting in slaked lime and an outlet for the waste gases to go out. The lowermost cylinder has an inlet for passing in chlorine gas and an outlet for the bleaching powder to come out.

Working of Hasenclever Plant

First of all dry slaked lime is entered into the Hasenclever plant through hopper. Then this dry slaked lime is moved forward by the revolving blades of the rotating shaft. In the meantime chlorine gas is passed through the lowermost cylinder which moves up to the upper cylinders and reacts with the dry slaked lime coming downward to form bleaching powder. This bleaching powder comes out through the outlet at the bottom of innermost cylinder and collected in a vessel.

Properties of Bleaching Powder

1. Bleaching powder is a yellowish white powder with characteristic strong smell of chlorine.
2. It is soluble in water.
3. Reaction with carbon dioxide:- When bleaching powder is exposed in air then it reacts with carbon dioxide gas present in air to produce calcium carbonate and chlorine gas:

   

4. Available Chlorine:- The amount of chlorine which is liberated during reaction of bleaching powder with carbon dioxide or sulphuric acid or hydrochloric acid is called available chlorine. The superiority of bleaching powder can be estimated by the amount of bleaching powder. The greater the amount of available chlorine, more superior will the bleaching powder is. A good sample of bleaching powder contains 35 to 38 % of available chlorine.
5. Reaction with dilute hydrochloric acid:- When bleaching powder is reacted with dilute hydrochloric acid then all the chlorine gas present in it is liberated:

   

6. Reaction with dilute sulphuric acid:- When bleaching powder is reacted with dilute sulphuric acid then all the chlorine gas present in it is liberated:

   

Uses of Bleaching Powder

1. Bleaching powder is used for bleaching cotton, linen, wood pulp and washing clothes. Its bleaching action is due to the release of chlorine gas from it.
2. It is used for making unshrinkable wool.
3. It is used for disinfecting drinking water.
4. It is also used in the manufacture of chloroform, which is used as an anesthetic in hospitals by doctors before surgery.
5. It is used as an oxidizing agent in many chemical industries.

Test your understanding and answer these questions:

1. What is chemical name and formula of bleaching powder?
2. How bleaching powder is manufactured?
3. What are uses of bleaching powder?