Question

Explain the industrial method of preparation of bleaching powder with a neat diagram.

Answer 1

Bleaching powder is extensively used as a disinfectant and in bleaching of paper. Bleaching powder is known by calcium hypochlorite as its chemical name. The chemical formula of bleaching powder is $CaOC{{l}_{2}}$.

Complete step by step solution:

Let’s look at the process of production of bleaching powder:
- The raw material required in its production are:

1. Lime-stone
2. $C{{l}_{2}}$gas

Now, let’s look at the process:
- In the first step, quick lime is produced. It is produced from limestone. The limestone is heated at a very high temperature at about $898{}^\circ C$ to decompose it into quicklime and carbon dioxide gas.
$CaC{{O}_{3}}\,\xrightarrow{898{}^\circ C}\,CaO\,+\,C{{O}_{2}}$
- In the next step, the quick lime is treated with water to give slaked lime which is the major raw material for the production of bleaching powder.
$CaO\,+\,{{H}_{2}}O\,\to \,Ca{{(OH)}_{2}}$
- In the last step, the slaked lime is treated with $C{{l}_{2}}$ gas to give bleaching powder.
- The chlorine gas is passed through the slaked lime in chlorine chambers where solid bleaching powder is collected as the product. The temperature is kept below $35{}^\circ C$.
- The slaked lime is poured from above while the chlorine gas is passed from a lower level.
$Ca{{(OH)}_{2}}\,+\,C{{l}_{2}}\,\to \,Ca{{(ClO)}_{2}}CaC{{l}_{2}}Ca{{(OH)}_{2}}.2{{H}_{2}}O$

Note: Students can get confused in the chemical formula of bleaching powder. $CaOC{{l}_{2}}$is the representation of bleaching powder while the actual formula is $Ca{{(ClO)}_{2}}CaC{{l}_{2}}Ca{{(OH)}_{2}}.2{{H}_{2}}O$. So, if the formula is asked then students must choose the second one.
The bleaching action is due to hypochlorite ion and it is permanent.