Question

# A metal carbonate X on reacting 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, and it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G, and Z.

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Solution

## Calcium:Calcium is a metal having an atomic number $20$ and atomic symbol $\mathrm{Ca}$.Reaction of Calcium carbonate with acid:When Calcium carbonate $\left({\mathrm{CaCO}}_{3}\right)$ reacts with Hydrochloric acid $\left(\mathrm{HCl}\right)$, it produces Calcium chloride $\left({\mathrm{CaCl}}_{2}\right)$ along with the liberation of carbon dioxide$\left({\mathrm{CO}}_{2}\right)$ and water$\left({\mathrm{H}}_{2}\mathrm{O}\right)$.The chemical reaction can be depicted as: ${\mathrm{CaCO}}_{3}\left(\mathrm{s}\right)+\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{CaCl}}_{2}\left(\mathrm{aq}\right)+{\mathrm{CO}}_{2}\left(\mathrm{g}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$Reaction of ${\mathrm{CO}}_{2}$ with slaked lime:When carbon dioxide gas is passed through Slaked lime or Calcium hydroxide $\left({\mathrm{CaOH}}_{2}\right)$, it gives calcium carbonate $\left({\mathrm{CaCO}}_{3}\right)$.The chemical reaction can be depicted as: $\mathrm{Ca}{\left(\mathrm{OH}\right)}_{2}\left(\mathrm{aq}\right)+{\mathrm{CO}}_{2}\left(\mathrm{g}\right)\to {\mathrm{CaCO}}_{3}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$Electrolysis of brine solution:Brine solution is a solution of sodium chloride $\left(\mathrm{NaCl}\right)$ and water $\left({\mathrm{H}}_{2}\mathrm{O}\right)$.The gas that is obtained at the anode during electrolysis of brine is passed on dry slaked lime is Chlorine gas.The reaction taking place at the anode is depicted as:$2{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)\to {\mathrm{Cl}}_{2}\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}$Reaction of chlorine gas with dry lime water:Lime water is Calcium hydroxide $\left({\mathrm{CaOH}}_{2}\right)$.When chlorine gas is passed on dry lime water, it gives bleaching powder which is used for disinfecting water.When dry chlorine gas is passed over the dry slaked lime, calcium oxychloride$\left({\mathrm{CaOCl}}_{2}\right)$ is formed.The chemical reaction can be depicted as: $\mathrm{Ca}{\left(\mathrm{OH}\right)}_{2}\left(\mathrm{s}\right)+{\mathrm{Cl}}_{2}\left(\mathrm{g}\right)\to {\mathrm{CaOCl}}_{2}\left(\mathrm{aq}\right)+{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{l}\right)$Hence, X is calcium carbonate $\left({\mathrm{CaCO}}_{3}\right)$, Y is slaked lime $\left({\mathrm{CaOH}}_{2}\right)$, Z is bleaching powder $\left({\mathrm{CaOCl}}_{2}\right)$, and G is chlorine gas $\left({\mathrm{Cl}}_{2}\right)$.

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