Q. A compound $X$ on heating gives a colourless gas. This residue is dissolved in water to obtain $Y.$ Excess $CO_{2}$ is bubbled through aqueous solution of $Y$ when $Z$ is formed. $Z$ on gentle heating gives back $X.$ The $X$ is
A) $CaCO_{3}$
B) $Ca\left( HCO_{3} \right)_{2}$
C) $Na_{2}CO_{3}$
D) $NaHCO_{3}$
Explanation
(a)
$CaCO_{3}\overset{\ \ \ \ \ \mathrm{\Delta}\ \ \ \ \ }{\rightarrow}\ CaO + CO_{2}$
$(X)$
$CaO + H_{2}O\ \longrightarrow Ca(OH)_{2}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (Y)$
$Ca(OH)_{2} + 2CO_{2} \longrightarrow Ca\left( HCO_{3} \right)_{2}$
(Z)
$Ca\left( HCO_{3} \right)_{2}\overset{\ \ \ \ \ \mathrm{\Delta}\ \ \ \ \ }{\rightarrow}\ CaCO_{3}\ \rightarrow CO_{2} + H_{2}O\$
(X)
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.