Question

When ${\text{M}}{{\text{g}}_3}{{\text{N}}_2}$reacts with \[{{\text{H}}_2}{\text{O}}\], then how many types of gaseous product(s) is/are formed?

Answer 1

Hint: Alkaline earth metal nitrides have the formula \[{{\text{M}}_3}{{\text{N}}_2}\]. When they are treated with water, a gaseous product is formed. When magnesium nitride is heated with very high temperature say, \[700 - {1500^ \circ }{\text{C}}\], the products formed are magnesium and nitrogen gas.

Complete step by step information:
Metal nitrides having formula \[{{\text{M}}_3}{{\text{N}}_2}\]are prepared by two methods
By treating with dry nitrogen at high temperature.
$3{\text{M}} + {{\text{N}}_2}\xrightarrow{\Delta }{{\text{M}}_3}{{\text{N}}_2}$
By passing ammonia at high temperature.
\[3{\text{M}} + 2{\text{N}}{{\text{H}}_3} \to {{\text{M}}_3}{{\text{N}}_2} + 3{{\text{H}}_2}\]
It produces hydrogen gas.
Magnesium nitride is a compound made up of magnesium and nitrogen. It appears as greenish yellow powder at room temperature. When it is treated with water, it hydrolyses and forms magnesium hydroxide ${\text{Mg}}{\left( {{\text{OH}}} \right)_2}$. The gaseous product formed is ammonia gas. The equation involving the reaction is:
\[{\text{M}}{{\text{g}}_3}{{\text{N}}_{2\left( {\text{s}} \right)}} + {{\text{H}}_2}{{\text{O}}_{\left( {\text{l}} \right)}} \to {\text{Mg}}{\left( {{\text{OH}}} \right)_{2\left( {{\text{aq}}} \right)}} + {\text{N}}{{\text{H}}_{3\left( {\text{g}} \right)}}\]
The complete balanced chemical equation is given below.
\[{\text{M}}{{\text{g}}_3}{{\text{N}}_{2\left( {\text{s}} \right)}} + 6{{\text{H}}_2}{{\text{O}}_{\left( {\text{l}} \right)}} \to 3{\text{Mg}}{\left( {{\text{OH}}} \right)_{2\left( {{\text{aq}}} \right)}} + 2{\text{N}}{{\text{H}}_{3\left( {\text{g}} \right)}}\]

Therefore only one type of gaseous product is formed which is the ammonia gas.

Additional information:
To balance the equation, we have to keep the same number of elements in reactant side and product side. Since three magnesium is there in the reactant side. Two nitrogen are there in the reactant side. So we can put 2 for ammonia molecules. 2 hydrogen are there in the reactant side and now 12 hydrogen are there in the product side. So by putting 6 to water molecules, the equation is balanced.

Note: When the amount of magnesium nitride and water molecule is given, we can calculate the amount of magnesium hydroxide produced in the reaction. Also we can calculate the percentage yield when all the amounts are given. Among alkaline earth metals’ nitrides, lithium nitride is the only compound which is stable.