Question

$5\%\left(w/v\right)$ solution of glucose is isotonic with $2\%\left(w/v\right)$ solution of a non-volatile non electrolyte substance at same ‘T’. The molecular mass of the substance will be:
[0.77 Mark]

• A. $36\text{g}$
• B. $72\text{g}$
• C. $78\text{g}$
• D. $90\text{g}$

Answer 1

The correct option is B $72\text{g}$

For isotonic solution,${\pi }_1={\pi }_2$
$\Rightarrow C_1=C_2(\because \pi =CRT)$
$\Rightarrow \frac{5\times 1000}{180\times 100}=\frac{2\times 1000}{M\times 100}$
$M=\frac{2\times 180}{5}=72\text{g}$