Question

A chemical A is used for the preparation of washing soda to recover ammonia. When $C{O_2}$ is bubbled through an aqueous solution of A, the solution turns milky. It is used in white washing due to disinfectant nature. What is the chemical formula of A?

A. $Ca{(HC{O_3})_2}$
B. $CaO$
C. $Ca{(OH)_2}$
D. $CaC{O_3}$

Answer 1

Hint : The preparation of washing soda to is done with the help of a process known as Solvay process in which soda ash is obtained which is predominantly sodium carbonate $N{a_2}C{O_3}$ and the substrates are brine solution acting as a source of sodium chloride $NaCl$ and limestone acting as a source of calcium carbonate $CaC{O_3}$ . The reaction is as follows:
$2NaCl + CaC{O_3}\; \to N{a_2}C{O_3}\; + {\text{ }}CaC{l_2}$

Complete step by step solution :
As we are familiar with the Solvay process rather than the production of $N{a_2}C{O_3}$ it has another purpose of recovering ammonia in which calcium hydroxide $Ca{(OH)_2}$ is used it reacts with ammonium chloride to give us ammonia and calcium chloride with water as a product the reaction is as follows:
$2N{H_4}Cl + Ca{(OH)_2} \to 2N{H_3} + CaC{l_2} + {H_2}O\;$
And when the calcium hydroxide is bubbled with $C{O_2}$ that is carbon dioxide the solution turns milky this is due to the fact that there is a formation of $CaC{O_3}$ , and the reaction is as follows:
$Ca{(OH)_2} + C{O_2} \to CaC{O_3} \downarrow + {H_2}O\;$
And the Calcium hydroxide is versatile as it is used in white washing due to its disinfectant nature.
Since, Calcium hydroxide matches all the above statements so it constitutes compound A and the correct answer is Option C.
Additional Information: Calcium hydroxide was called as slaked lime initially and is an inorganic compound with the chemical formula $Ca{(OH)_2}$ . It is a colourless crystal or white powder and is produced when quicklime chemically known as calcium oxide is mixed with water. It is known to have many common names slaked lime, builder’s lime etc.

Note : The product from the Solvay’s process is in the form of sodium bicarbonate ( $NaHC{O_3}$ ) precipitate which is then converted to the final product, sodium carbonate washing soda: $N{a_2}C{O_3}$ , by calcination method at temperature of about $160 - {230^o}C$ , giving us water and carbon dioxide as by-products, and the reaction is as follows:
$2\;NaHC{O_3}\; \to \;N{a_2}C{O_3}\; + \;{H_2}O\; + \;C{O_2}$