Question

A $1.2\%$ solution of $NaCl$ is isotonic with $7.2\%$ solution of glucose. Calculate the van't Hoff factor of $NaCl$

• A. $1.5$
• B. $1.95$
• C. $1.70$
• D. $1.25$

Answer 1

The correct option is B $1.95$

The two solutions are isotonic means both the solutions have same osmotic pressure.
For, $1.2\%$ solution of $NaCl$, osmotic pressure, ${\pi }_1=iCRT=i\frac{\frac{1.2}{58.5}}{V}RT$
For, $72\%$ solution of glucose, osmotic pressure,
${\pi }_2=CRT=\frac{\frac{7.2}{180}}{V}RT$
According to the question,
${\pi }_1={\pi }_2$
$\Rightarrow i\frac{\frac{1.2}{58.5}}{V}RT=\frac{\frac{7.2}{180}}{V}RT$
$\Rightarrow i=\frac{7.2\times 58.5}{180\times 1.2}=1.95$