Question

Question 45.
A metal carbonate X on reacts with acid and gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at the anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identify X, Y, G and Z.

Answer 1

X is calcium carbonate and the gas evolved is carbon dioxide, when calcium carbonate reacts with acid.

${\text{CaCO}}_3+\text{Dil}.2\text{HCl}⟶{\text{CaCl}}_2+{\text{H}}_2\text{O}+{\text{CO}}_2\uparrow$

Solution Y is lime water ${\text{Ca(OH}}_2)$ because, when ${\text{CO}}_2$ is passed through it, it gives the carbonate back as shown by the given equation.

$\underset{\text{Y}}{{\text{Ca(OH)}}_2}+{\text{CO}}_2⟶\underset{\text{X}}{{\text{CaCO}}_3}\downarrow +{\text{H}}_2\text{O}$

The gas evolved at the anode during electrolysis of brine is chlorine (G).

$\underset{\text{Sodium chloride (brine)}}{2\text{NaCl}}+2{\text{H}}_2\text{O}\stackrel{\text{Electrolysis}}{⟶}2\text{NaOH}+\underset{\text{Chlorine gas (G)}}{{\text{Cl}}_2\text{(g)}}+{\text{H}}_2\text{(g)}$

When chlorine gas is passed through dry ${\text{Ca(OH)}}_2$ (Y), it produces bleaching powder (Z) used for disinfecting drinking water.

${\text{Ca(OH}}_2)+{\text{Cl}}_2⟶\underset{\text{Bleaching powder (Z)}}{{\text{CaOCl}}_2}+{\text{H}}_2\text{O}$

Hence, Z is calcium oxy-chloride ${\text{CaOCl}}_2$ or bleaching powder.