Question

What is the Van’t Hoff factor?

Answer 1

Van’t Hoff factor is named after the Dutch physical chemist Jacobus Henricus Van’t Hoff, who won the first Nobel Prize in chemistry. The Van’t Hoff factor is a measure of the effect of a solute on colligative properties such as osmotic pressure, relative lowering in vapour pressure, the elevation of boiling point and freezing point depression.

Complete answer:
The Van't Hoff factor explains how solutes affect the colligative properties of solutions. The letter ‘ $i$ ’ stands for Van't Hoff factor. The Van't Hoff factor is the ratio of the concentration of particles formed when a substance is dissolved to the substance's mass concentration.
The Van't Hoff factor describes the degree to which a substance associates or dissociates in a solution. When a non-electrolytic material is dissolved in water, for example, the value of $i$ is usually $1$ . The value of $i$ on the other hand, is equal to the total number of ions present in one formula unit of an ionic molecule when it forms a solution in water.
$CaC{l_2}$ , for example, has an ideal Van't Hoff factor of $3$ because it dissociates into one $C{a^{2 + }}$ ion and two $C{l^ - }$ ions. However, some of these ions in the solution associate with one another, resulting in a reduction in the overall number of particles in the solution.
$i$ is less than $1$ when solute particles are associated in solution.
$i$ is greater than $1$ when solute particles dissociate in solution.
When solute particles in solution do not dissociate or associate, $i$ equals $1$ .

Note:
It is important to note that for electrolytic solutions, the measured Van't Hoff factor is usually lower than the expected value (due to the pairing of ions). The more the ion charge, the higher the deviation.