Question

What is the vapour pressure of the solution containing 34.2 g of sucrose per 100 g of water at ${25}^{o}C?$ The vapour pressure of water at ${25}^{o}C$ is 23.75 mm.

• A. 20.3 mm
• B. 23.10 mm
• C. Unpredictable
• D. 23.33 mm

Answer 1

The correct option is D 23.33 mm

we have,

$\frac{P_B^0-P_t}{P^0}=x_A$ = $\frac{n_A}{n_A+n_B}$

let vapour pressure of solution = x

moles of sucrose = $\frac{givenweight}{molarweight}$ = 0.1 moles

moles of water = $\frac{100}{18}$ = 5.55

so, we have

$\frac{P_B^0-P_t}{P^0}=x_A$ = $\frac{n_A}{n_A+n_B}$

$\frac{23.75-x}{23.75}=x_A$ = $\frac{0.1}{0.1+5.55}$

so, vapour pressure of solution (x) = 23.33 mm