Question

A gaseous compound of $85.7\%$ by mass carbon and $14.3\%$ by mass hydrogen.Its density is $2.28g/litre$ at $300K$ and $1.0$ atm pressure. Determine the molecular formula of the compound.

• A. $C_2{H}_2$
• B. $C_2{H}_4$
• C. $C_4{H}_8$
• D. $C_4{H}_{10}$

Answer 1

Answer: (C)

$C_4{H}_8$

We know, $PV=nRT$ $d=$ density $=2.28\frac{g}{litre}$

$PV=\frac{m}{M}RT$ $R=0.0821$

$PM=\frac{m}{V}RT$ $P=1$ atm

$M=\frac{dRT}{P}$ $T=300k$

$M=\frac{2.28\times 0.0821\times 300}{1}$

$M=56$ gms

It is the molecular mass of $C_4{H}_8$ and it also has $85.77$% of carbon and $H=14.3$%.