An expression for the degree of dissociation of a weak electrolyte. For example, if a weak acid dissociates in water HA⇌H++A− the dissociation constant Ka is given by Ka = α2n/(1 – α)V where α is the degree of dissociation, n the initial amount of substance (before dissociation), and V the volume. If α is small compared with 1, then α2 = KV/n; i.e. the degree of dissociation is proportional to the square root of the dilution. The law was first put forward by Wilhelm Ostwald to account for electrical conductivities of electrolyte solutions.
Ka = α2n/(1 – α)V