Liquid Solution

Step 1: Find the mole fraction of water.
The solution has a mole fraction of solute =0.02.
Mole fraction of water =1 minus mole fraction of solute.
So, χ‌water ‌=1−0.02=0.98
Step 2: Use Raoult's Law to relate vapour pressures.
Raoult's law says: Vapour pressure of solution = Vapour pressure of pure water × Mole fraction of water.
p‌solution ‌=p‌water ‌×χ‌water ‌
We know p‌solution ‌‌‌=34.65mmHg and χ‌water ‌=0.98.
So, 34.65=p‌water ‌×0.98
Step 3: Solve for the vapour pressure of pure water.
Divide both sides by 0.98 :
p‌water ‌=‌

34.65

0.98

=35.36mmHg