In the vapour above an ideal binary solution of two volatile liquids at equilibrium, the vapour phase is always richer in:
Athe component of lower mole fraction
Bthe component of higher molar mass
Cthe less volatile component
Dthe more volatile component
Answer & Solution
Correct answer: D. the more volatile component
1. The partial pressure of a component scales with its pure vapour pressure $p^0$.
2. The more volatile component has the higher $p^0$ and so contributes a larger partial pressure.
3. Since vapour mole fraction $y_i = p_i / p_{total}$, the vapour is always richer in the more volatile component.
_Source: NCERT Class 12 Chemistry Ch 1 "Solutions", p.10_
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