When mass fraction of solute in a very dilute solution is doubled, its mole fraction is — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

In a highly dilute solution, the moles of solute n is much smaller than the moles of solvent N (n << N). Thus, the mole fraction of solute X_solute = n / (n + N) ≈ n / N = (w_solute / M_solute) / (W_solvent / M_solvent). This shows that the mole fraction is directly ∝ the mass of the solute (w_solute) and consequently to its mass fraction. Thus, doubling the mass fraction doubles the mole fraction.