Question

96. 12 gm of an alkaline earth metal gives 14.8 g
of its nitride. The atomic mass of metal is
g
​

Answer 1

Let us consider that atomic mass of alkaline earth metal is M g/mol.

given mass of alkaline earth metal = 12gm

chemical formula of metal nitride = $M_3N_2$

so, molecular mass of metal nitride = (3M + 14 × 2) = (3M + 28) g/mol.

or, mass fraction of metal = mass of metal/molecular mass

or, 12/14.8 = 3M/(3M + 28)

or, 30/37 = 3M/(3M + 28)

or, 30M + 280 = 37M

or, 280 = 7M

or, M = 40 g/mol .

hence, atomic mass of metal is 40g/mol.