Question

Which of the following representations of $i$ (van’t Hoff factor) is not correct ?

• A. $i=\frac{\text{Observed colligative property}}{\text{Expected colligative property}}$
• B. $i=\frac{\text{Normal molecular mass}}{\text{Observed molecular mass}}$
• C. $i=\frac{\text{Number of molecules actually present}}{\text{Number of molecules expected to be present}}$
• D. $i=\frac{\text{Total number of particles taken before association/dissociation}}{\text{Number of particles after association/dissociation}}$

Answer 1

Answer: (D)

The van't Hoff theory describes that substances in dilute solution obey the ideal gas laws, resulting to the osmotic pressure formula $\pi =(n/V)RT=[Ci]RT$ where $R$ is the gas constant, $T$ the absolute temperature, and [Ci] the molar concentration of solutei in dilute solution (1).
It is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is also defined as the measure of the tendency of a solution to take in pure solvent osmosis.