Van’t Hoff factor (i)

Definition

The van't Hoff factor (i) is a measure of the effect of solute particles on colligative properties. It represents the number of particles into which a solute dissociates in solution.

5 Must Know Facts For Your Next Test

1. The van't Hoff factor is used in calculating boiling point elevation, freezing point depression, and osmotic pressure.
2. For non-electrolytes that do not dissociate in solution, the van't Hoff factor is equal to 1.
3. For strong electrolytes that fully dissociate, the van't Hoff factor equals the total number of ions produced per formula unit.
4. In real solutions, especially with weak electrolytes or at high concentrations, the observed van't Hoff factor may differ from the theoretical value due to ion pairing or incomplete dissociation.
5. The van’t Hoff factor can affect properties like vapor pressure lowering by altering the number of active particles in solution.

Review Questions

• What does the van’t Hoff factor indicate about a solute in solution?
• How does the van’t Hoff factor influence freezing point depression?
• Why might the actual van’t Hoff factor differ from its theoretical value?

Related terms

Colligative Properties: Properties that depend on the number of solute particles in a solution and not on their identity.

Boiling Point Elevation: The increase in boiling point of a solvent upon addition of a non-volatile solute, proportional to the molal concentration and influenced by the van’t Hoff factor.

Freezing Point Depression: The decrease in freezing point of a solvent due to addition of a solute, proportional to molality and affected by the van’t Hoff factor.