The vapour pressure of a solution of a non-volatile, non-electrolyte solute in a solvent is 95% of t — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

Relative lowering of vapour pressure: $(P^\circ - P)/P = n/N$. Given $P = 0.95 P^\circ$, $(P^\circ - 0.95P^\circ)/0.95P^\circ = 0.05/0.95 = 1/19$. So $n/N = 1/19 \Rightarrow N/n = 19$. Given $M_{solvent} = 0.3 M_{solute}$. Mass ratio $W_{solvent} / W_{solute} = (N \cdot M_{solvent}) / (n \cdot M_{solute}) = 19 \times (0.3 M_{solute} / M_{solute}) = 19 \times 0.3 = 5.7$. Thus, the ratio is 5.7:1 or 57:10. Therefore, correct answer is B.