The vapour pressure of a solvent decreases by 10 mm of Hg
when a non-volatile solute was added to the solvent. The
mole fraction of the solute in the solution is 0.2. What should
be the mole fraction of the solvent if the decrease in the
vapour pressure is to be 20 mm of Hg ?
(a) 0.8 (b) 0.6 (c) 0.4 (d) 0.2
Answers
Answered by
12
The mole fraction of the solvent when the decrease in the vapour pressure is 20 mm of Hg is (b) 0.6
1. We have ∆P/P° = Xsolute
2. A/Q,
10/P°=0.2 ..........(i)
3. 20/P°=1- Xsolvent .........(ii)
4. From (i),
P°=50
5. Thus, from (ii),
X solvent = 1 - 20/50
= 1 -0.4
=0.6
6. Thus, the correct answer is (b) 0.6
Answered by
6
The mole fraction of the solvent is 0.6
Option (B) is correct.
Explanation:
We know that:
Po - Ps = Po x Mole fraction of solute
10 = Po x 0.2 -------(1)
20 = Po x X2 -------(2)
Solving equation (1) and (2) we get.
X2 = 0.4
X1 (Solvent) = 1 - 0.4 = 0.6
Thus the mole fraction of the solvent is 0.6
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