Question

$A \,5\%$ solution of cane sugar $(M.W. = 342)$ is isotonic 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

Being isotonic, molar concentration of cane sugar = molar concentration of substance $X$ $\frac{5}{342} \times \frac{1000}{100}$ $= \frac{1}{x} \times \frac{1000}{100}$ (let the molecular weight of $X = x$) $x = \frac{342}{5} = 68.4$