Question

Ammonia gas can be dried over by:
$\begin{aligned} & \text{A}\text{. CaC}{{\text{l}}_{2}} \\\ & \text{B}\text{. conc}\text{. }{{\text{H}}_{2}}\text{S}{{\text{O}}_{4}} \\\ & \text{C}\text{. }{{\text{P}}_{2}}{{\text{O}}_{5}} \\\ & \text{D}\text{. Quick lime} \\\ \end{aligned}$

Answer 1

The molecular formula of ammonia is $\text{N}{{\text{H}}_{3}}$. Calcium oxide is another name for quicklime / burnt lime. Ammonia is used as a refrigerant gas. It is an alkaline so also called basic gas.

Complete step by step solution:
-The preparation of ammonia is done by the heating of calcium hydroxide and ammonium chloride.
-The balanced reaction will be:
$\text{Ca}{{\left( \text{OH} \right)}_{2}}\text{ + 2N}{{\text{H}}_{4}}\text{Cl }\to \text{ CaC}{{\text{l}}_{2}}\text{ + 2N}{{\text{H}}_{3}}\ \text{+ 2}{{\text{H}}_{2}}\text{O}$
-Here, if the ammonia gas will be dried by passing it through concentrated sulphuric acid then it forms a complex of ammonium sulphate (IV) instead of drying.
-The reaction between ammonia and conc. sulphuric acid is:
$\text{2N}{{\text{H}}_{3}}\text{ + }{{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}\text{ }\to \text{ }{{\left( \text{N}{{\text{H}}_{4}} \right)}_{2}}\text{S}{{\text{O}}_{4}}\text{ }$
-So, option B is an incorrect answer.
-Similarly, ammonia gas also reacts with phosphorus pentoxide and forms a complex of ammonia and phosphorus and ammonia doesn't dry.
-The balanced reaction will be:
${{\text{P}}_{2}}{{\text{O}}_{5}}\text{ + 6N}{{\text{H}}_{3}}\text{ + 3}{{\text{H}}_{2}}\text{O }\to \text{ 2}{{\left( \text{N}{{\text{H}}_{4}} \right)}_{3}}\text{P}{{\text{O}}_{4}}$
-So, option C is also an incorrect answer.
-Now, when ammonia is dried with calcium chloride, it also reacts with it and forms a complex of calcium chloride and ammonia.
-We can see this process through the chemical reaction as given below:
$\text{CaC}{{\text{l}}_{2}}\text{ + 8N}{{\text{H}}_{3}}\text{ }\to \text{CaC}{{\text{l}}_{2}}\text{ }\cdot \text{ 8N}{{\text{H}}_{3}}$
-So, option A is also an incorrect answer.
-But it is observed that ammonia gas cannot react with the quick lime whose molecular formula is $\text{CaO}$. Instead, ammonia gas can be dried using quick lime because it reacts with moisture and forms calcium hydroxide.
-The balanced chemical reaction showing the reaction of quick lime with water is:
$\text{CaO + }{{\text{H}}_{2}}\text{O }\to \text{ Ca}{{\left( \text{OH} \right)}_{2}}$

Therefore, option D. is the correct answer.

Note: The presence of ammonia gas can be detected by the addition of sodium hydroxide in a solution. Then if ammonia is present in the solution the characteristic smell of it will come.