Question
Derive the relationship between relative lowering of vapour pressure and mole fraction of a volatiles liquid.
Solution
Answer:
for any solution the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction.
pA ∝ xA
pA x xA where pA is vapour pressure of solvent having mole fraction xA.
PA = P0A x A
But xA + xB = L
∴ xA = 1 – xB
When xB is mole fraction of non-voltile solute B
Pa = P0A (1–xB)
= p0A – p0A x B
Total vapour of solution is equal to pA as nonvolatile solute does not have any vapour pressure.
i.e., Total vapour pressure,
