A sample of air contains nitrogen and oxygen saturated with water vapour.The total pressure is 640 mm. The vapour pressure of water vapour is 40 mm and molar ratio of nitrogen and oxygen is ` 4 : 1`. Find out the partial pressures of `N_(2) and O_(2)`.

Explanation

Total pressure, `P_(N_(2))+P_(O_(2)) + P_(H_(2)O) = 640` mm
Vapour pressure of water vapour = 40 mm
`:. P_(N_(2)) + P_(O_(2)) = 640 - 40 = 600` mm
Mole fraction of nitrogen = 4/5
Mole fraction of oxygen = `1/5`
Partial pressure of `N_(2) = " total pressure" xx X_(N_(2)) = 600 xx 4/5 = 480` mm
Partial pressure of `O_(2) = 600 xx 1/5 = 120` mm