Van't Hoff Factor and Abnormal Molar Mass MCQ - Practice Questions with Answers

If a solute gets associated or dissociated in a solution, the actual number of particles are different from expected or theoretical consideration.

We know, that:

Thus, we can say that:

Again, we have:

Thus;

Suppose we have the solute A and it dissociates into B. Then the dissociation occurs as follows:

                           
At time t = 0         1          0

At time t = t       1 -       n

Thus, at time t = 0, initial number of solute particles = 1
And, at time t = t, observed number of solute particles = 1 -  + n
                                                                               = 1 + (n-1)

Thus, we know that:

where n = number of solute particles
          = Degree of dissociation

NOTE: For strong electrolytes,  = 1 

Suppose we have the solute A and it associates into (A)_n. Then the association occurs as follows:

                        
At time t = 0        1            0

At time t = t       1 -        /n

Now, initial number of solute particles = 1

And, observed number of solute particles = 1 -  + /n
                                                             = 1 + [1/n - 1]

Thus, van't Hoff factor is given as:

where,  is the degree of association