Question

For this reaction \[CaC{O_3}\,\underrightarrow \Delta \,A + {B_{(gas)}}\] $A\,\underrightarrow {{H_2}O}\,C\,\underrightarrow {C{l_2} + {{40}^0}C}\,D$
Product D is:
(A) $CaC{l_2}$
(B) $Ca{(OH)_2}$
(C) $CaC{l_2}.6{H_2}O$
(D) $CaOC{l_2}$

Answer 1

Hint: The given equation is of the thermal decomposition process of Calcium Carbonate (also called limestone). Under extreme temperature when limestone is heated it gets converted to its oxide and liberates a gas. The oxide which is formed when reacts with water forms a Hydroxide and then when it is treated with chloride it gets converted into an inorganic compound which works as a bleaching agent in the swimming pools.

Complete step by step answer:
When Calcium Carbonate is heated strongly, it undergoes thermal decomposition to yield Calcium oxide also known as lime and Carbon dioxide gas. It is an endothermic process.
\[CaC{O_3}\,\underrightarrow \Delta CaO + C{O_2}_{(gas)}\] \[\]
When lime is treated with water it gets converted into an alkaline solution known as slaked lime. It is an exothermic Reaction.
$CaO\,\underrightarrow {{H_2}O}Ca{(OH)_2}$
When this Slaked lime is treated with chloride it gets converted to calcium hypochlorite also known as bleaching agent. It is an exothermic process. It is used in cleaning swimming pools.
\[Ca{(OH)_2}\,\underrightarrow {C{l_2} + {{40}^0}C}\,CaOC{l_2}\]
Hence, $A$ is \[CaO\], $B$ is $C{O_2}$, $C$ is $Ca{(OH)_2}$ and $D$ is $CaOC{l_2}$.
And hence option D is the correct answer.

Additional information: In endothermic reactions the heat absorbs and cools the temperature of the surrounding while in an exothermic reaction heat is released into the surroundings leading to the rise in temperature.

Note:Limestone is a very commonly found rock that is used extensively for various purposes. Its Thermal decomposition involves a cycle of reaction from endothermic to exothermic in which calcium carbonate is decomposed into lime and $C{O_2}$ gas which on further reaction with water gives slaked lime which when treated with chloride gives you bleaching powder.