Question

The amount of glucose to be dissolved in 500 g of water so as to produce the same lowering in vapour pressure as that of 0.2 molal aqueous urea solution is:

• A. 9 g
• B. 18 g
• C. 36 g
• D. 1.8 g

Answer 1

Answer: (B)

18 g

For urea $M=0.2$

$M=\frac{\text{Moles of urea (n)}\times 1000}{\text{Mass of solvent}}$

Relative lowering of vapour pressure

$=\frac{0.2\times 18}{1000}=\frac{3.6}{1000}$ .........$\left(1\right)$

For glucose

Relative lowering in vapour pressure= $\frac{\text{Mass of glucose (W)}\times 18}{180\times 500}$

$=\frac{W}{5000}$ .........$\left(2\right)$

From (1) & (2),

$\frac{3.6}{1000}=\frac{W}{5000}$

$\Rightarrow W=18g$

Hence, the correct option is $B$