Van't Hoft factor

In physical chemistry, the Van't Hoft factor i is the number of moles of solute actually in a solution in water, per mole of solid solute added.

For example, glucose has a Van't Hoft Factor of 1 because one mole of glucose dissolved in water will result in one mole dissolved. The Van't Hoft Factor of sodium chloride is 2 because one mole will dissociate completely into one mole of Na⁺ and one mole of Cl^- for a total of 2 moles. Substances that dissociate partially, such as acetic acid have a fractional Van't Hoft factor, which is an average of the different dissociation states, weighted for the occurrence of each. That for acetic acid is just over 1 (representing the equlibrium between HC₂H₃O₂ and the ions H⁺ and C₂H₃O₂^-)