Question

Give the modified equations for the colligative properties for substances exhibiting abnormal molecular masses.

Answer 1

For substances showing abnormal molecular masses due to association or dissociation, the colligative property equations are modified by introducing the van’t Hoff factor (i), which adjusts for the actual number of particles in solution.

Here are the modified equations:

1. Relative lowering of vapour pressure:
   `(p^circ - p)/p^0 = i * chi_"solute"`
2. Elevation of boiling point:
   ΔT_b = i . K_b . m
3. Depression of freezing point:
   ΔT_f = i . K_f . m
4. Osmotic pressure:
   π = iCRT

These equations ensure accurate results when the solute doesn’t behave ideally by accounting for the change in particle number caused by association (i < 1) or dissociation (i > 1).