Question

A mixture of hydrogen and oxygen at one bar pressure contains $20\%$ by weight of hydrogen. Partial pressure of hydrogen will be ?

• A. $0.2bar$
• B. $0.4bar$
• C. $0.6bar$
• D. $0.8bar$

Answer 1

The correct option is D $0.8bar$

As the mixture contains $20\%$ by weight of hydrogen means 100 gm of the mixture contains 20 g of hydrogen, therefore 80 g of the mixture will be oxygen.

No. of moles of hydrogen $=\frac{\text{wt.}}{\text{mol. wt.}}=\frac{20}{2}=10\text{moles}$

No. of moles of oxygen $=\frac{\text{wt.}}{\text{Mol. wt.}}=\frac{80}{32}=2.5\text{moles}$

$\therefore$ Mole fraction of hydrogen $\left(X_{hydrogen}\right)=\frac{\text{Moles of hydrogen}}{\text{Total no. of moles}}=\frac{10}{12.5}=0.8$

As we know that

Partial pressure = mole fraction $\times$ pure pressure

Given that Pure pressure $=1\text{bar}$

$\therefore$ Partial pressure of hydrogen $=X_{hydrohen}\times P$

$\Rightarrow P_{hydrogen}=0.8\times 1=0.8\text{bar}$