199. Define Van’t Hoff factor. What is its value for a non-electrolytic solution?

Van’t Hoff introduced a factor ‘i’ called Van’t Hoff’s factor, to express the extent of association or dissociation of solutes in solution. It is ratio of the normal and observed molecular masses of the solute, i.e


$\mathrm{i} =\frac{ \mathrm{Normal} \mathrm{molecular} \mathrm{mass}}{\mathrm{observed} \mathrm{molecular} \mathrm{mass}}$

In case of association, observed molecular mass being more than the normal, the factor i has a value less than 1. But in case of dissociation, the Van’t Hoff’s factor is more than 1 because the observed molecular mass has a lesser value than the normal molecular mass. In case there is no dissociation the value of ‘i’ becomes equal to one.