Air is a mixture gases. It contains 20% by volume of O2 gas and 79% by volume of N2 gas at 298K. Water is in quilibrium with air at a pressure of 10 atmospheres. KH for O2 and N2 at 298 K are 3.30x107mm and 6.51x 107 mm respectively. Determine the composition of these gases in water.

Air is a mixture gases. It contains 20% by volume of O2 gas and 79% by

1.	Air is a mixture gases. It contains 20% by volume of O2 gas and 79% by volume of N2 gas at 298K. Water is in quilibrium with air at a pressure of 10 atmospheres. KH for O2 and N2 at 298 K are 3.30x107mm and 6.51x 107 mm respectively. Determine the composition of these gases in water.
Answer» ressure of air above WATER = P = 10 atm.partial PRESSURE of O2 in air above water = P1partial pressure of N2 above water = P2Volume of air above water = VVolume of O2 = V1 = 0.20 VVolume of N2 = V2 = 0.79 Vlet n1 moles of OXYGEN and n2 moles of N2 be present in air in volume V.Let n = total number of moles of gases in airFrom Daltons' law of partial pressures and the law of ideal gas mixture: Henry's law for solubility : where p = partial presssure of the gas above the liquid in equilibrium with solution Henry's constant c = molar concentration of the gas in moles/Litre in the solution c1 = concentration of O2 in water = mol/Litre = 4.606 * 32 * 10⁻⁵ gm/Litre = 1.474 mg/kg of water = 0.1474 % of water by mass or 8.291 * 10⁻⁵ moles/100 moles of waterc2 = concentration of N2 in water = mol/Litre = 2.582 mg/Litre = 0.2582 % of water by mass = 16.6* 10⁻⁵ moles/100 moles of water