What is the concentration of O₂ in a freshwater stream in equilibrium with air at 25^oC and 1.0 bar?
Express the answer in grams of O₂ per kg of solvent. (Henry’s law constant for O₂ is 1.3x10^-3 mol/kgxbar

The mole fraction of O2 in air is 0.21 and assuming the total pressure is 1.0bar, the partial pressure of O2 is 0.21bar. Using this pressure for Pg in Henry`s law we have...Solubility of O2 = KHPg = 1.3×10−3mol/Kg.bar (0.21 bar) = 2.7 × 10-4 mol/lThis concentration in grams per liter can then be calculated using the molar mass of O2.Solubility of O2 = 2.7×10−4mol/Kg × 32.0g/mol = 0.0087 g/KgThis concentration of O2 (8.7 mg/Kg) is quite low, but it is sufficient to provide the oxygen required by aquatic life.