Question

12 g of an alkaline earth metal gives 14.8 g of its nitride. Atomic weight of metal is:

• A. 12
• B. 20
• C. 40
• D. 14.8

Answer 1

The correct option is C 40

The general reaction between alkaline metal and nitrogen is given as:
$3M+N_2⟶M_3{N}_2$
Let, atomic weight of M = $x$
So,
no. of moles in 12 g of M = $\frac{12}{x}$
no. of moles in 14.8 g of nitride = $\frac{14.8}{3x+28}$

From the reaction shown above,
3 moles of M furnish 1 mole of nitride.
Hence,
$\frac{1}{3}\times \frac{12}{x}$$=\frac{14.8}{3x+28}$
$\Rightarrow x=40$