Question

A solution is obtained by dissolving 12 g of urea (mol. wt.60) in a litre of water. Another solution is obtained by dissolving 68.4 g of cane sugar (mol. wt. 342) in a litre of water at the same temperature. The lowering of vapour pressure in the first solution is

• A. Same as that of $2^{nd}$ solution
• B. Nearly one-fifth of the $2^{nd}$ solution
• C. Double that of $2^{nd}$ solution
• D. Nearly five times that of $2^{nd}$ solution

Answer 1

Answer: (A)

We know that in the first solution number of the moles of urea $\frac{\text{Mass of urea}}{\text{m.wt. of urea}}\times\frac{1}{V}$
$=\frac{12}{60}\times\frac{1}{1}=0.2$ and
In second solution the number of moles of cane sugar
$=\frac{\text{Mass of cane sugar}}{\text{m.wt. of cane sugar}} = \frac{68.4}{342}\times\frac{1}{1}=0.2$