Which statement correctly describes Raoult's law for an ideal solution of two volatile liquids A and B?
AVapour pressure is independent of composition
BThe partial vapour pressure of each component equals its pure-component vapour pressure
CTotal vapour pressure depends only on the more volatile component
DThe partial vapour pressure of each component is proportional to its mole fraction in the solution
Answer & Solution
Correct answer: D. The partial vapour pressure of each component is proportional to its mole fraction in the solution
Raoult's law for component $A$: $p_A = p_A^* \chi_A$, where $p_A^*$ is the vapour pressure of pure $A$ and $\chi_A$ is its mole fraction in the liquid. The same form applies to $B$. Total vapour pressure: $p = p_A^* \chi_A + p_B^* \chi_B$.
The key word is **proportional**, with proportionality constant equal to the pure-component pressure. Option A would only hold at $\chi = 1$ (pure component).
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