Question

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

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

Answer 1

Answer: (C)

68.4

Molar conc. of cane sugar,

$=\frac{5}{342}\times \frac{1000}{100}=\frac{50}{342}$

molar conc. of solution,

$X=\frac{1}{m}\times \frac{1000}{100}=\frac{10}{m}$

$\frac{10}{m}=\frac{50}{342}$

$\Rightarrow m=68.4$

Hence, the correct option is $C$