Question

A $20.0c{m}^2$ mixture of $CO,C{H}_4$ and He gases is exploded by an electric discharge at room temperature with excess of oxygen. The volume contraction is found to be $13.0c{m}^3$. A further contraction of $14.0c{m}^3$ occurs when the residual gas is treated with KOH solution. Find out the volume percentage of CO in gaseous mixture.

• A. 25%
• B. 50%
• C. 20%
• D. 37.5%

Answer 1

Answer: (D)

37.5%

Since oxygen is present in excess, the volume of oxygen is not considered in calculating volume contractions.
First volume contraction corresponds to water which is $13c{m}^3$.
$C{H}_4+2O_2\to C{O}_2+2H_{2}O$
Hence, the volume of $C{H}_4$ is 6.5 $c{m}^3$. This is also equal to the volume of $C{O}_2$ obtaoined from $C{H}_4$.
Hence, the volume of $C{O}_2$ obtained from $CO$ is $14-6.5=7.5c{m}^3$
This also corresponds to the volume of $CO$
$2CO+O_2\to 2C{O}_2$
Hence, the volume percentage of $CO$ in the mixture is $\frac{7.5\times 100}{20}=37.5$ %.