1) In a mixture of two gases 1 and 2, express the molar fraction of a component based on pressures!
2) Calculate the mole fraction of oxygen in the exhaled air, whereby the partial pressure of this gas is $160\;mmHg$
1) Ideal gas law:
$X_1$ $=$ $\frac{n_1}{n_1+n_2}$ $=$ $\frac{\frac{P_1V}{RT}}{\frac{P_1V}{RT}+\frac{P_2V}{RT}}$ $=$ $\frac{P_1}{P_1+P_2}$ $=$ $\frac{P_1}{P}$
with:
$P_1$: Partial pressure of gas 1
$P_2$: Partial pressure of gas 2
$P$: Pressure of the exhaled air = $760\;mmHg$
$V$: Volume of the exhaled air
$R$: Ideal gas constant
2)
$X_{O_2}$ $=$ $\frac{P_{O_2}}{P}$ $=$ $\frac{160}{760}$ $=$ $0.211$
