Association
The joining of solute molecules in solution into larger aggregates, reducing the effective number of particles.
Formula / equation
nA → Aₙ
Unit
Dimensionless
In depth
Association is common for carboxylic acids in non-polar solvents, where two molecules form a cyclic pair of hydrogen bonds. Because the number of independent particles falls, the van't Hoff factor drops below one and the observed colligative effect is smaller than expected.
Examples in the real world
Benzoic acid dimerising in benzene; hydrogen fluoride forming chains in the liquid state.