Question

A metal carbonate $X$ on reacting with an acid gives a gas which when passed through a solution $Y$ gives the carbonate back. On the other hand, a gas $G$ is obtained at the anode during electrolysis of brine and is passed on dry $Y$, it gives a compound $Z$, used for disinfecting drinking water. Identify $X,Y,G$ and $Z$.
A. $X \to$ Hydrogen bicarbonate, $Y \to$Lime water, $G \to$Chlorine gas, $Z \to$ Calcium carbonate
B. $X \to$ Calcium oxychloride, $Y \to$Lime water, $G \to$Chlorine gas, $Z \to$ Calcium carbonate
C. $X \to$ Hydrogen carbonate, $Y \to$ Calcium oxychloride, $G \to$Chlorine gas, $Z \to$ Limewater
D. $X \to$ Calcium carbonate, $Y \to$ Lime water, $G \to$Chlorine gas, $Z \to$ Calcium oxychloride

Answer 1

A metal carbonate when heated, gives carbon dioxide which turns the lime water milky because of the formation of the metal carbonate again. The gas which is at anode must be a derivative of the electrolytic solution and when passed through the lime water gives away a water disinfecting substance which kills the bacteria and other microorganisms present in the water.

Complete answer:
Metal carbonates on reaction with a strong acid, produces metal chloride and releases carbon dioxide along with water. Thus, the metal carbonate is calcium carbonate in the reaction. Calcium carbonate gives carbon dioxide gas when it reacts with hydrochloric acid.

$CaC{O_3} + 2HCl \to CaC{l_2} + C{O_2} + {H_2}O$
When carbon dioxide; so formed; is passed through the lime water, lime water turns milky because of the formation of calcium carbonate.
$Ca{\left( {OH} \right)_2} + C{O_2} \to CaC{O_3} + {H_2}O$
When the brine solution is electrolysed, chlorine gas gets deposited over the anode which gives calcium oxychloride (Bleaching powder) on passing over slaked lime. The bleaching powder is used in disinfecting the drinking water.
$Ca{\left( {OH} \right)_2} + C{l_2} \to CaOC{l_2} + {H_{2}}O$
Bleaching powder is used for disinfecting drinking water.
Therefore, metal carbonate $X$ is calcium carbonate, the solution $Y$ is lime water (Calcium hydroxide), the gas $G$ is chlorine gas and dry $Y$ is dry calcium hydroxide (dry slaked lime) and compound $Z$ is bleaching powder (Calcium oxychloride).

Thus, the correct option is (D) $X \to$ Calcium carbonate, $Y \to$ Lime water, $G \to$Chlorine gas, $Z \to$ Calcium oxychloride.

Note: These reaction steps are primarily used in the industries for the preparation of bleaching powder which acts as a disinfectant for the drinking water and kills the microorganisms present in it. The calcium carbonate is used in making white chalk and also in making marbles. It can also be used in the formation of calcium chloride which is used largely in the chemical laboratories for qualitative analysis.