CHEMISTRY OF WHITEWASHING THE WALL

Whitewashing is process of applying a white colour solution to walls to get a shining finish.

Chemical process behind whitewashing of wall

Powdered calcium oxide(quick lime) when mixed with water produce aqueous solution of calcium hydroxide(slaked lime).

Calcium oxide(quick lime) + water ——> calcium hydroxide (slaked lime) 

CaO + H₂O ——> Ca(OH)₂

This is an exothermic reaction 

This aqueous solution of calcium hydroxide is applied on wall as whitewash. This calcium hydroxide when applied to the wall will react slowly with carbon dioxide in the atmosphere and produce thin layer of calcium carbonate on the wall. It will take almost two or three days for the formation of calcium carbonate to give a white shining appearance to the wall. Chemical equation of reaction 

Calcium hydroxide + carbon dioxide—> Calcium carbonate + water

Ca(OH)₂ + CO₂ —> CaCO₃ + H₂O