Difference - experimental value of van't Hoff factor differ from the calculated value

Question

How does existence of ion pairs cause the experimental value of van't Hoff factor differ from the calculated value?

Answer 1

Ideally, the van't Hoff factor is an integer based on the number of particles that a substance will dissociate into.

For instance K2SO4 would dissociate into two K+ ions and a sulfate ion, for a total of three particles.  This might be the case for a very, very dilute solution, but for more concentrated solutions a positive and a negative ion can be attracted and act as a single unit (ion pairing), rather than as two separate ones, and this can reduce the effect on the boiling point elevation or freezing point depression.  This, in essence, reduces the value of i.