Question

A solution of a substance ‘X’ is used for white washing. Name the substance ‘X’ and write its formula.

Answer 1

Hint – In this question use the concept that the substance that is widely used for white washing reacts with water to form slaked lime that is\[Ca{\left( {OH} \right)_2}\]. Use this to get the reactant side and thus the chemical formula of the compound can be known too.

Complete answer:
As we know that the substance used for white washing is calcium oxide also known as quick line or burnt lime or lime, it is an alkaline earth flux and the chemical formula of calcium oxide is CaO.
So when we mix calcium oxide with water it makes a solution calcium hydroxide \[Ca{\left( {OH} \right)_2}\].
Which is used for white washing, and the chemical reaction is shown below,
$ \Rightarrow CaO + {H_2}O \to Ca{\left( {OH} \right)_2}$
So the substance X is calcium oxide (CaO).
So this is the required answer.

Note – The reason that CaO is used for white washing is that on reaction of CaO with water if forms calcium hydroxide, if this calcium hydroxide \[Ca{\left( {OH} \right)_2}\] is reacted with $C{O_2}$in air this forms $CaC{O_3}$. It is hard and gives a shiny finish to the walls hence it is preferred as white washing agent.