Question

A compound of carbon, hydrogen, and nitrogen contains the three elements in the respective ratio of $9:1:3.5$. Calculate the empirical formula. If the molecular weight of the compound is $108$ and the molecular formula is $C_x{H}_y{N}_z$, then find the value of $x,y$ and $z$.

• A. $x=6,y=8,z=2$
• B. $x=5,y=6,z=3$
• C. $x=6,y=10,z=2$
• D. $x=7,y=8,z=1$

Answer 1

Answer: (A)

$x=6,y=8,z=2$

In a certain compound, the ratio of $C:H:N=9:1:3.5$
Molar ratio of $C:H:N$ $=\frac{9}{12}:\frac{1}{1}:\frac{3.5}{14}=0.75:1:10.25$
Integer ratio $=\frac{0.75}{0.25}:\frac{1}{0.25}:\frac{0.25}{0.25}=3:4:1$
Therefore, the empirical formula is $C_3{H}_{4}N$.
Empirical weight $=12\times 3+1\times 4+14=54$ g.
Given the molecular weight is $108$ g.
$n=\frac{Mw}{EFw}=\frac{108}{54}=2$
Molecular formula $=C_6{H}_8{N}_2$