Question

Calculate the vapour pressure of a solution at ${100}^{o}C$ containing 3 g of cane sugar in 33 g of water.

• A. 756.36 mm of Hg
• B. 766.36 mm of Hg
• C. 746.36 mm of Hg
• D. 456.36 mm of Hg

Answer 1

Answer: (A)

756.36 mm of Hg

Vapour pressure of pure water (solvent) at${100}^{o}C$, $p^o$ = 760mm

Vapour pressure of solution, p = ?

Wt. of solvent , W = 33g

Wt. of solute , w = 3g

Mol. wt. of water = 18

Mol. wt. of sugar $(C_{12}{H}_{22}{O}_{11}$)= 342

According to Raoult’s law ,

$\frac{p^o-p}{p^o}$ = $\frac{wM}{WM}$

$p=p^o-\frac{w\times M}{m\times W}\times p^o$

$p=760-\frac{3\times 18}{342\times 33}\times 760$

$p=756.33mmHg$