The four colligative properties of the dilute solutions help in calulating the molecular mass of sthe solute which is often called observen molecular mass. It may be same as the theoretical molecular mass (calculated form rthe molecular formula) if the solute behaves normally in solution. In case, it undergoes association or dissociation. the observed molar mass gives different results. The nature of the in solution is expressed in terms of Van't Hoff factor (i) which may be 1 (if the solute behave normally), less than 1 (if the solute associates) and more than 1 (if the solute dissociates). The extent of association of dissociation is repreented by `lapha` which is :`alpha=underset(("For association"))((i-1)/(1//n-1))or underset(("for dissoviation"))((i-1)/(n-1))`
(16) The molar mass ofd the solute sodium hydrxide obtained form the measurement of osmotic pressure of its aqueous solution at `27^(@)C` is 25 g `mol^(-1)`. Therefore, The precentage ionisation of solution is :

Options

A. 75
B. 60
C. 80
D. 70

Answer

b

Explanation

`i=("Normal molar mass")/("Abnormal molar mass")`
= `((40"g mol"^(-1)))/((25"g mol"^(-1)))=1.6`
`alpha=(i-1)/(n-1)=(1.6-1)/(2-1)=0.6`
% ionisation = 60.