Question

Write the chemical name of bleaching powder and write its properties.

Answer 1

Hint: Bleaching powder is a solid combination of chlorine (\[C{{l}_{2}}\]) and slaked lime \[Ca{{\left( OH \right)}_{2}}\]. It was introduced in 1799 by Scottish chemist Charles Tennant. It is a pale yellow or nearly white colored inorganic powder. It smells like chlorine, i.e., pungent and irritating odor.

Complete step by step answer:
Chemically, bleaching powder is known as calcium hypochlorite or calcium oxychloride, with the chemical formula \[Ca{{\left( OCl \right)}_{2}}\].
Bleaching powder is prepared by passing chlorine gas (\[C{{l}_{2}}\]) over slaked lime \[Ca{{\left( OH \right)}_{2}}\].

\[2Ca{{\left( OH \right)}_{2}}+2C{{l}_{2}}\to CaC{{l}_{2}}+Ca{{\left( OCl \right)}_{2}}+2{{H}_{2}}O\]

It is soluble in cold water. It has wide applications in different industries. For example, it is used for bleaching wood pulp in the paper industry, bleaching cotton and linen in the textile industry, used for disinfecting drinking water supply and also used in the manufacturing of chloroform.

When bleaching powder \[Ca{{\left( OCl \right)}_{2}}\] reacts with carbon dioxide present in atmosphere, it undergoes following reaction,

\[2Ca{{\left( OCl \right)}_{2}}+2C{{O}_{2}}\to 2CaC{{O}_{3}}+2C{{l}_{2}}\uparrow +{{O}_{2}}\uparrow \]

This is the reason behind the chlorine like smell of bleaching powder.
When reacted with dilute acids, say aqueous sulphuric acid (\[{{H}_{2}}S{{O}_{4}}\]), it liberates whole of its chlorine.

\[Ca{{\left( OCl \right)}_{2}}+{{H}_{2}}S{{O}_{4}}\to CaS{{O}_{4}}+{{H}_{2}}O+C{{l}_{2}}\]

The chlorine obtained by this reaction is called available chlorine. The value of bleaching powder in the market is directly proportional to the amount of available chlorine liberated by action with dilute acids. Higher the amount of available chlorine, greater will be the price of bleaching powder.
In the presence of insufficient dilute acids, bleaching powder acts as a bleaching agent, due to the liberation of nascent oxygen [O]. The bleaching action can be understood well by following reactions:

\[2Ca{{\left( OCl \right)}_{2}}+{{H}_{2}}S{{O}_{4}}\to CaC{{l}_{2}}+CaS{{O}_{4}}+~2HClO\]

This hypochlorous acid (\[HClO\]) further decomposes to give hydrochloric acid and nascent oxygen.

\[2HClO\to 2HCl+2\left[ O \right]\]

Note: Baking soda and vinegar can be a better substitute to bleach for laundry, because chlorine can cause acute and chronic health risks on its prolonged uses, by affecting the respiratory system.