Degree of Ionisation
The fraction of dissolved electrolyte molecules that have broken into ions at equilibrium.
Formula / equation
α = ionised / total
Unit
Dimensionless
In depth
Strong electrolytes have a degree of ionisation close to one at all concentrations, while weak electrolytes have small values that increase on dilution. The quantity is measured by conductivity, by pH, or from colligative property measurements through the van't Hoff factor.
Examples in the real world
0.1 M ethanoic acid has α ≈ 0.013, whereas 0.1 M HCl has α ≈ 1.