Question

Compound ‘A’ when dissolve in water gives compound ‘B’ and liberates heat. Compound ‘A’ is used In whitewashing .Compound ‘B’ reacts with CO2 to form a white precipitate of compound ‘C’.Identify

Answer 1

A - CaO calcium chloride. B - Ca(OH)2 calcium hydroxide. C - CaCO3 calcium carbonate. Reactions: CaO + H2O = Ca(OH)2 + heat. It is used in whitewashing. Ca(OH)2 + CO2 = CaCO3 + H2O

Answer 2

$\bold{\begin{array}{l}{\mathrm{A}+\text { water } \longrightarrow \mathrm{B}} \\ {\mathrm{B}+\mathrm{CO}_{2} \rightarrow \mathrm{C}}\end{array}}$

We know that Slaked lime with chemical formula $\mathrm{Ca}(\mathrm{OH})_{2}$ is used for whitewashing which can be prepared by the reaction of quicklime that is CaO with water. Hence A is CaO and B is $\bold{\mathrm{Ca}(\mathrm{OH})_{2}}$ here.  

$\mathrm{CaO}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}$

$\mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{CO}_{2} \rightarrow \mathrm{CaCO}_{3}(\mathrm{C})+\mathrm{H}_{2} \mathrm{O}$

And $\mathrm{CaCO}_{3}$ is the white precipitate which is formed by the reaction of slaked lime and carbon dioxide.