Question

In a compound $C,H$ and $N$ are present in $9:1:3.5$ by weight. If molecular weight of the compound is $108$, then the molecular formula of the compound is

• A. $C_2{H}_6{N}_2$
• B. $C_3{H}_{4}N$
• C. $C_6{H}_8{N}_2$
• D. $C_9{H}_{12}{N}_3$

Answer 1

Answer: (C)

Element	Element ratio	Atomic mass	Relative no. of atoms	Simplest ratio
Carbon	9	12	$\frac{9}{12}=0.75$	3
Hydrogen	1	1	$\frac{1}{1}=1$	4
Nitrogen	3.5	14	$\frac{3.5}{14}=0.25$	1

$\therefore$ Empirical formula of the compound $=C_3{H}_{4}N$
$n(12\times 3+1\times 4+14\times 1)=108$
or, $n(36+4+14)=108$
or, $54n=108$
or, $n=2$
$\therefore$ Molecular formula of the compound $=C_6{H}_8{N}_2$