The vapour pressure of the solution is 23.4 torr.
Use Raoult’s Law to calculate the vapour pressure:
p₁ = χ₁p₁°
where
χ₁ = the mole fraction of the solvent
p₁ and p₁° are the vapour pressures of the solution and of the pure solvent
The formula for vapour pressure lowering Δp is
Δp = p₁° - p₁
Δp = p₁° - χ₁p₁° = p₁°(1 – χ₁) = χ₂p₁°
where χ₂ is the mole fraction of the solute.
Step 1. Calculate the mole fraction of glucose
n₂ = 18.0 g glu × (1 moL glu/180.0 g glu) = 0.1000 mol glu
n₁ = 95.0 g H_2O × (1 mol H_2O/18.02 g H_2O) = 5.272 mol H_2O
χ₂ = n₂/(n₁ + n₂) = 0.1000/(0.1000 + 5.272) = 0.1000/5.372 = 0.018 62
Step 2. Calculate the vapour pressure lowering
Δp = χ₂p₁° = 0.018 62 × 23.8 torr = 0.4430 torr
Step 3. Calculate the vapour pressure
p₁ = p₁° - Δp = 23.8 torr – 0.4430 torr = 23.4 torr
