Ostwald dilution law
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 K a is given by K a = α2 n/(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.
K a = α2 n/(1 – α)V