Question

The vapour pressure of pure water at ${26}^{\circ }C$ is 25.21torr. What is the vapour pressure of a solution which contains 20.0g of glucose in 70g of water?

• A. 27.9torr
• B. 25.9torr
• C. 24.5torr
• D. 32.0torr

Answer 1

The correct option is C 24.5torr

$n_1=\frac{20}{180}=0.111;n_2=\frac{70}{18}=3.89$
$\frac{P_0-P_S}{P_0}=\frac{n_1}{n_1+n_2}$
$\frac{25.21-P_S}{25.21}=\frac{0.111}{0.111+3.89}=0.0277$
$25.21-P_S=0.0277\times 25.21=0.699$
$P_S=25.21-0.699=24.5torr$