Question

What is the mole fraction of the KCl solute in a 1.00 molal aqueous solution?

Answer 1

$n = \frac{m}{M}$

$M(H_2O) = 18\ \frac{g}{mol}$

$m = 1\ kg; n(H_2O) = \frac{1000\ g}{18\ g/mol} \approx 55.56\ mol$

1 molal means 1 mol of solute in 1 kg of a solvent

$X_{KCl} = \frac{1\ mol}{1\ mol + 55.56\ mol} =\frac{1}{56.56} \approx 0.01768$

Answer: $X_{KCl} = 0.01768$