A gas mixture exerts partial pressures of $0.60$ bar of gas A and $0.40$ bar of gas B over water at a fixed temperature. The Henry's law constants (for $p = K_{H} x$ ) are $K_{A} = 4.0 \times 1 0^{4}$ bar and $K_{B} = 1.0 \times 1 0^{5}$ bar. The ratio of dissolved mole fractions $x_{A} / x_{B}$ is

Answer: A

Henry's law gives

x = p / K_{H}

for each gas.

x_{A} = 0.60/ (4.0 \times 1 0^{4}) = 1.50 \times 1 0^{- 5}

and

x_{B} = 0.40/ (1.0 \times 1 0^{5}) = 4.00 \times 1 0^{- 6}

. So

x_{A} / x_{B} = 3.75

. The ratio of pressures alone (1.50) ignores the different

K_{H}

values.