Question

$12$ gms of alkaline earth metal gives $14.8$ gms of its nitride. What is the atomic mass of metal?

• A. 15
• B. 20
• C. 30
• D. 40

Answer 1

The correct option is D 40

Let the alkaline earth metal be M. It will form a dispositive ion. The balanced chemical equation for the formation of nitride is as given below.

$3M+N_2\to M_3{N}_2$

Let M g/mol by the molar mass of the metal. The molar mass of the metal nitride will be $(3M+28)$ g/mol.

Now 3 moles of the metal gives 1 mole of nitride. Hence, $\frac{12}{3M}=\frac{14.8}{3M+28}$

$12M+112=14.8M$

$2.8M=112$

$M=40$

Hence, the molar mass of the alkaline earth metal is $40$ g/mol.