Air containing 80% nitrogen by mole is in contact with water at a total pressure of 5.0 atm. Take K_H for N2 in water as 8.0x10^4 atm (for p=K_Hx) and ignore water vapour. The mole fraction of dissolved N2 is

JEE Main levelSingle correct optionDifficulty 2 of 3so124

Air containing $80%$ nitrogen by mole is in contact with water at a total pressure of $5.0$ atm. Take $K_{H}$ for $N X_{2}$ in water as $8.0 \times 1 0^{4}$ atm (for $p = K_{H} x$ ) and ignore water vapour. The mole fraction of dissolved $N X_{2}$ is

The partial pressure of

N X_{2}

0.80 \times 5.0 = 4.0

atm. Henry's law gives

x = p / K_{H} = 4.0/ (8.0 \times 1 0^{4}) = 5.0 \times 1 0^{- 5}

. Using the total pressure would give

6.3 \times 1 0^{- 5}

, which is wrong.