Question

A mixture of hydrogen and oxygen contains 40% hydrogen by mass when the pressure is 2.2 bar. The partial pressure of hydrogen is _______ bar. (Nearest integer)

Answer 1

40% w/w hydrogen gas is given in mixture of $H_2$ and oxygen.
Wt. of $H_2$ = 40 g
Wt. of $O_2$ = 60 g
$X_{H2}=\frac {n_{H_2}}{n_{H_2}+n_{O_2}}$

$=\frac {\frac {40}{2}}{\frac {40}{2}+\frac {60}{32}}$

$=\frac {20}{20+1.875}$

$=\frac {20}{21.875}$
$=0.914$
$P_{H_2}=X_{H_2}×PT$
$P_{H_2}=0.914×2.2$
$P_{H_2}=2.01$
$P_{H_2}≃2$ bar

So, the answer is $2$ bar.