When a non-volatile solute is dissolved in a volatile solvent, the vapour pressure of the solution:
AFirst increases, then decreases
BDecreases
CIncreases
DRemains the same
Answer & Solution
Correct answer: B. Decreases
The non-volatile solute occupies some of the surface that would otherwise emit solvent vapour, reducing the rate of vaporization. Hence $P_{solution} < P^0_{solvent}$ — Raoult's law gives $P = x_1 P_1^0$ with $x_1 < 1$.
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