Question

A 5% solution of cane sugar (MW = 342) isisotonic with 1% solution of substance X. The molecular weight of X is

• A. 171.2
• B. 68.4
• C. 34.2
• D. 136.2

Answer 1

Answer: (B)

68.4

Answer 2

Given $5 \%$ solution of Cane Sugar
$\Rightarrow 5 \,g$ of solute present in $100\, ml$ of solution
For isotonic solutions $\pi_{1}=\pi_{2}$
$\Rightarrow c _{1}= c _{2}$
$\frac{5}{342 \times 0.1}=\frac{1}{ M _{2} \times 0.1}$
$\Rightarrow M _{2}=\frac{342}{5}=68.4$