Question

The molar mass of the solute sodium hydroxide obtained from the measurement of the osmotic pressure of its aqueous solution at $27^{\circ} C$ is $25 \,g \,mol ^{-1}$. Therefore, its ionization percentage in this solution is

• A. 75
• B. 60
• C. 80
• D. 70

Answer 1

Answer: (B)

60

Answer 2

van't Hoff factor,
$i=\frac{\text { observed molar mass }}{\text { calculated molar mass }}$
$=\frac{40}{25}=1.6$
Since, sodium hydroxide is binary electrolyte,
$i=[1+(2-1) \alpha](\alpha=$ degree of ionisation)
$1.6=(1+\alpha) \alpha$
$=1.6-1=0.6=60$