Question

A 5% solution of cane sugar (molar mass 342) is isotonic with 1% of a solution of an unknown solute. The molar mass of unknown solute in g/mol is:

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

Answer 1

Answer: (B)

68.4

Answer 2

$\pi_{1} = \pi_{2}$ $C_{1} = C_{2} \frac{5 / 342}{0.1} = \frac{1/M}{0.1}$ $\frac{5}{342} = \frac{1}{M} \quad\Rightarrow\quad M = \frac{342}{5} = 68.4 \,gm/mol$