Question

Ammonia gas is not prepared by:
[A] Reduction of sodium nitrite or nitrate by the reaction of zinc dust and sodium hydroxide.
[B] Hydrolysis of calcium cyanamide.
[C] Heating ammonium chloride with slaked lime
[D] Heating of ${{\left( N{{H}_{4}} \right)}_{2}}C{{r}_{2}}{{O}_{7}}$

Answer 1

To solve this you must know that ammonia gas comprises nitrogen and hydrogen. Its formula is $N{{H}_{3}}$ . Here you simply find out the correct answer by writing down the reactions given in the options and finding out the one in which ammonia gas is not evolved.

Complete step by step solution:
To solve this question, we will go through all of the options mentioned and see the reaction and find out whether ammonia gas is released during the reaction or not.
Firstly, we have reduction of sodium nitrite or nitrate by the reaction of zinc dust and sodium hydroxide.
When we add zinc powder with sodium hydroxide in sodium nitrite or sodium nitrate, the reaction moves forward by corrosion of zinc and reduction of the nitrite and the nitrate. It leads to the formation of sodium zinc oxide product and water as well as evolution of ammonia gas takes place. We can write the reaction as-
\$\begin{aligned} & NaN{{O}_{3}}+4Zn+7NaOH\to 4N{{a}_{2}}Zn{{O}_{2}}+N{{H}_{3}}+2{{H}_{2}}O \\\ & NaN{{O}_{2}}+3Zn+5NaOH\to 3N{{a}_{2}}Zn{{O}_{2}}+N{{H}_{3}}+{{H}_{2}}O \\\ \end{aligned}$
Then we have hydrolysis of calcium cyanamide. Calcium cyanamide upon reaction with water decomposes and liberates ammonia gas and forms calcium carbonate. For this reason it is also used as a fertilizer. We can write the reaction as-
$CaC{{N}_{2}}+3{{H}_{2}}O\to 2N{{H}_{3}}+CaC{{O}_{3}}$
Next we have heating ammonium chloride with slaked lime. We know that slaked lime is calcium hydroxide. When it reacts with ammonium chloride, it forms calcium chloride and water and ammonia gas is evolved. We can write the reaction as-
$N{{H}_{4}}Cl+Ca{{\left( OH \right)}_{2}}\to CaC{{l}_{2}}+2N{{H}_{3}}+2{{H}_{2}}O$
And lastly, we have heating of ${{\left( N{{H}_{4}} \right)}_{2}}C{{r}_{2}}{{O}_{7}}$ . When we heat ammonium dichromate, thermal decomposition takes place and nitrogen, chromium oxide and water is produced. We can write the reaction as-
${{\left( N{{H}_{4}} \right)}_{2}}C{{r}_{2}}{{O}_{7}}\xrightarrow{\Delta }{{N}_{2}}+C{{r}_{2}}{{O}_{3}}+{{H}_{2}}O$
Here, ammonia gas is not produced.

Therefore, the correct answer is option [D] Heating of ${{\left( N{{H}_{4}} \right)}_{2}}C{{r}_{2}}{{O}_{7}}$.

Note: We know that ammonia gas is an alkaline gas and its chemical formula is $N{{H}_{3}}$. It has a strong ammoniacal odour that can be easily distinguished. Ammonia gas is used as a refrigerant i.e. for cooling purposes. It is also used in the purification of water supplies and manufacture of plastics, explosives and many more chemical compounds. Ammonia is often found in house-hold cleaning reagents.