sblock Elements 2 Question 22
24. Calcium burns in nitrogen to produce a white powder which dissolves in sufficient water to produce a gas $A$ and an alkaline solution. The solution on exposure to air produces a thin solid layer of $B$ on the surface. Identify the compounds $A$ and $B$.
(1996, 3M)
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Solution:
- $A=\mathrm{NH} _{3}, B=\mathrm{CaCO} _{3}$.
Reactions involved are :
$$ \begin{aligned} & 3 \mathrm{Ca}+\mathrm{N} _{2} \xrightarrow{\text { Heat }} \mathrm{Ca} _{3} \mathrm{~N} _{2} \\ & \mathrm{Ca} _{3} \mathrm{~N} _{2}+6 \mathrm{H} _{2} \mathrm{O} \longrightarrow 3 \mathrm{Ca}(\mathrm{OH}) _{2}+\underset{A}{2 \mathrm{NH} _{3}} \\ & \mathrm{Ca}(\mathrm{OH}) _{2}+\underset{\text { (From air) }}{\mathrm{CO} _{2}} \longrightarrow \underset{B}{\mathrm{CaCO} _{3}}+\mathrm{H} _{2} \mathrm{O} \end{aligned} $$
