Question

What is the maximum value of Van’t Hoff factor for $AlC{l_3}$ ?

Answer 1

Hint: The Van’t Hoff factor is the measure of the effect of a solute on the colligative properties like osmotic pressure, relative lowering in vapor pressure, boiling point-elevation and freezing-point depression.

Complete answer:
The Van’t Hoff factor is defined as the ratio between the actual concentration of particles produced when the substance is dissolved and the concentration of the substance as calculated from its mass. For most non-electrolytes dissolved in water, the Van’t Hoff factor is one. For most of the ionic compounds dissolved in water, the Van’t Hoff factor is equal to the number of discrete ions present in a formula unit of the substance. This is true for ideal solutions only, because occasionally ion pairing occurs in solution. To get the maximum value of the Van't Hoff factor, we take the dissociation constant as one. This is because aluminium chloride undergoes $100\% $ dissociation and every molecule of aluminium chloride has turned into one $A{l^{ + 3}}$ ion and three $C{l^ - }$ ions i.e. total four ions are produced. So, the Van’t Hoff factor will be equal to four.
Therefore, the maximum value of Van’t Hoff factor for $AlC{l_3}$ is $4$ .

Note:
When solute particles are associated in a solution, the Van’t Hoff factor will be less than one. When solute particles dissociate in a solution, the Van’t Hoff factor will be greater than one. When the solute particles neither associate nor dissociate in a solution, the Van’t Hoff factor will be equal to one.