Question

Which one of the following is present as an active ingredient in bleaching powder for bleaching action?
A. $\text{Ca}{{\left( \text{OCl} \right)}_{2}}$
B. $\text{Ca}{{\text{O}}_{2}}\text{Cl}$
C. $\text{CaC}{{\text{l}}_{2}}$
D. $\text{CaOC}{{\text{l}}_{2}}$

Answer 1

Active ingredient means the substance in bleaching powder that is responsible for the bleaching action. The active ingredient can be found by knowing what is bleaching powder, its reactions and properties. It is an inorganic compound formed of chlorine, oxygen and calcium. It is also called as chloride of lime.

Complete answer:
Bleaching powder is formed by the reaction of chlorine gas $\left( \text{C}{{\text{l}}_{2}} \right)$ on calcium hydroxide $\left[ \text{Ca}{{\left( \text{OH} \right)}_{2}} \right]$ , the reaction is $2\text{Ca}{{\left( \text{OH} \right)}_{2}}+2\text{C}{{\text{l}}_{2}}\to \text{CaOC}{{\text{l}}_{2}}+\text{CaC}{{\text{l}}_{2}}+2{{\text{H}}_{2}}\text{O}$. The compound $\left( \text{CaOC}{{\text{l}}_{2}} \right)$ formed is bleaching powder. Its chemical name is calcium hypochlorite. It is further responsible for bleaching action.
The bleaching action of bleaching powder is due to the formation of nascent oxygen, when bleaching powder reacts with water. The reaction is $2\text{CaOC}{{\text{l}}_{2}}+2{{\text{H}}_{2}}\text{O}\rightleftharpoons \text{CaC}{{\text{l}}_{2}}+\text{Ca}{{\left( \text{OH} \right)}_{2}}+2\text{HClO}$.
The compound $\text{HClO}$ formed immediately breaks into hydrogen chloride and gives away nascent oxygen. $2\text{HClO}\rightleftharpoons \text{HCl}+\left[ \text{O} \right]$. This nascent oxygen formed reacts with coloured materials and leaves the solution colourless.
The correct of this question is $\text{CaOC}{{\text{l}}_{2}}$ is present as an active ingredient in bleaching powder for bleaching action.
So, the correct answer is “Option D”.

Additional Information:
Application of calcium hypochlorite:
(1) The solution of calcium hypochlorite could be used as a sanitizer.
(2) Calcium hypochlorite is a general oxidizing agent, thus used in many organic reactions.
(3) It is commonly used to sanitize swimming pools and disinfect drinking water.
(4) It is also used in the haloform reactions to manufacture chloroform.

Note: Sometimes, confusion rises between calcium oxychlorides and calcium hypochlorite. The name calcium oxychloride does not immediately refer to calcium hypochlorite, but is only applicable to the mixed calcium basic chloride compound which remains unreacted in the bleaching powder, Like $\text{CaC}{{\text{l}}_{2}}.2\text{Ca}{{\left( \text{OH} \right)}_{2}}$.