Question

A 5% solution of cane sugar (mol. mass = 342) is isotonic with 1% solution of a substance X. The molecular mass of X is:

• A. $34.5$
• B. $68.4$
• C. $136.8$
• D. $171.2$

Answer 1

The correct option is B

$68.4$

Explanation for correct answer:-

Option (B) $68.4$

Step 1: Given data

$5\%$ solution of cane sugar = $5g$ of solute present in$100ml$

Step 2: Formula Used

For isotonic solutions, osmotic pressure condition is

${\mathrm{\pi }}_1={\mathrm{\pi }}_2$ and concentration conditions is,

$c_1=c_2$

Concentration = $\frac{Givenmass(inpercentage)}{Molarmass}$

Step 3: Calculation of molar mass,

By putting the respective values in the following formula

$$\begin{gathered} \frac{5}{342\times 0.1}=\frac{1}{M_2\times 0.1} \\ {M}_2=\frac{342}{5} \\ {M}_2=68.4 \end{gathered}$$