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At 298 K, the Henry’s law constant for oxygen is 1.4 × 10⁻³ mol L⁻¹ atm⁻¹. If oxygen is at a partial pressure of 0.5 atm, what mass of oxygen will dissolve in 100 mL of water at 298 K?

1. 1.4 g
2. 3.2 g
3. 22.4 mg
4. 2.24 mg

Correct answer: 2.24 mg

Solution

Solubility = 1.4e-3 * 0.5 = 7e-4 mol/L; in 100 mL that is 7e-5 mol = 2.24e-3 g = 2.24 mg, not 1.4 g.

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