Question

A compound X on heating gives a colourless gas. The residue is dissolved in water to obtained Y. Excess CO2 is bubbled through aqueous solution of Y, Z is formed. Z on gently heating gives back X. The compound X is:

• A. CaCO3
• B. Na2CO3
• C. Ca(HCO3)2
• D. K2CO3

Answer 1

CaCO3 $\longrightarrow$CaO + CO2 , CaO + H2O $\longrightarrow$Ca(OH)2 ,

X Y

Ca(OH)2 + 2CO2$\longrightarrow$Ca(HCO3)2 , Ca(HCO3)2 $\longrightarrow$CaCO3 + H2O + CO2

Z