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States of Matter

Section: Chemistry

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Question : 5 of 31

Marks: +1, -0

At

T(\mathrm{K})

, hydrogen and oxygen gases are mixed in the ratio of

1: 2

by mass in a closed vessel of volume '

V

' litres. If the total pressure of gaseous mixture is ' p ' atm, the partial pressure of oxygen (in atm ) is

[AP EAPCET 23 May 2025 S1]

$\; \frac{p}{9}$
9p
$\; \frac{8p}{9}$
$\; \frac{p}{6}$

Solution:

Assume a total mass : 1 g of

\mathrm{H}_2

and 2 g of

\mathrm{O}_2

n_{\mathrm{H}_2} = \frac{\;\text{Given mass}\;}{\;\text{Molar mass}\;} = \frac{1}{2} = 0.5\;\text{mol}

Similarly,

n_{\mathrm{O}_2} = \frac{2}{32} = 0.0625\;\text{mol}

\; \text{Total moles}\;\; = n_{\;\text{Total}\;} = n_{\mathrm{H}_2} + n_{\mathrm{o}_2}

\; = 0.5625\;\text{mol}

Mole fraction of

\mathrm{O}_2

\chi_{\mathrm{o}_2} = \frac{n_{\mathrm{o}_2}}{n_{\;\text{total}\;}} = \frac{0.0625}{0.5625} = \frac{1}{9}

Partial pressure of

\mathrm{O}_2

p_{\mathrm{O}_2} = \chi_{\mathrm{O}_2} \cdot p_{\;\text{total}\;} = \frac{p}{9}\;\text{atm}

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