Question

10 g glucose (molar mass 180) and 20 g of sucrose (molar mass 342) are dissolved in 100 g of water. What will be the vapour pressure of the resultant solution if the vapour pressure of water is 35 mm Hg?

Answer 1

Mass of glucose = 10 g
No. of moles of glucose = 0.0556
Mass of sucrose = 20 g
No. of moles of sucrose = 0.0585
Mass of water = 100 g
No. of moles of water = 5.556
Total number of moles = 5.556+0.0585+0.0556
$=5.67$
Mole fraction of water $=\frac{5.556}{5.67}$
Vapour pressure of solution = Mole fraction of water $\times P_0$
$=\frac{5.556}{5.67}\times 35=34.3mmHg$