Question

A 5% by mass of an aqueous solution of $A$ of molar mass 342 g mol${}^{-1}$ is isotonic with 0.878% by mass of an aqueous solution of another substance B. The molar mass of $B$ in g mol${}^{-1}$ is:

• A. 120
• B. 180
• C. 60
• D. 90

Answer 1

Answer: (C)

60

Isotonic solution has same concentration.

$C_1=C_2$

$\frac{5}{342}=\frac{0.878}{\text{Molar mass of B}}$

So $5\times M=0.878\times 342$

So $M=60.052$

Hence, option C is correct.