Question

$12\, g$ of an alkaline earth metal gives $14.8\, gm$ of its nitride. Atomic weight of the metal is

• A. 12
• B. 20
• C. 40
• D. 14.8

Answer 1

Answer: (C)

40

Answer 2

Let the alkaline earth metal be A $\therefore3A+N_{2} \rightarrow A_{3}N_{2}$ $\Rightarrow \frac{Molecular\, mass\, of\, compd.}{Atomic \,mass\, of \,metal}=\frac{Wt. of compd.}{Wt. of metal}$ Let atomic mass of metal be x $\Rightarrow$ Molecular mass of compound $= 3x + 28$ $\Rightarrow \frac{3x+28}{3x}=\frac{14.8}{12} \Rightarrow x=40$