Law of dilution

The Ostwald's dilution law describes the degree of dissociation of weak electrolyte, ie, the fraction of free particles in a solution using the mass action law. According to this relationship, the degree of dissociation α increases with decreasing Einwaagekonzentration to c0 ( increasing dilution ). Therefore, weak electrolytes are almost completely dissociated at sufficient dilution. The relationship was discovered by Wilhelm Ostwald.

If a solution is diluted by adding water, ie reduced to the Einwaagekonzentration c0 of the substance, so does the degree of dissociation to α, since the dissociation constant Kd must remain the same. Conversely decreases with a further feed stream, that is, increasing the Einwaagekonzentration, the proportion of the ions in the solution and thus also the equivalent conductivity Λ.

Additive

Wilhelm Ostwald, the law derived with conductivity studies.

If, for the degree of dissociation of the above equation

The result for the conductivity following relationship:

Ostwald now made ​​simplifying assumptions for the determination of dissociation constants:

1 In weakly dissociated molecules

The term varies with the dilution only slightly, so you can roughly use the expression as a function of dilution factor.

2 The determination of two weakly dissociated particles

In the determination of two dissociation constants of weak electrolytes only the corresponding ratios of the above expression must be used.

3 In case of strong electrolytes

Here, the return value is determined from at increasing dilution.

One difficulty prepared the determination of the limiting conductivities of ions of weak organic acids, bases which are necessary for the determination of dissociation constants. However, alkali metal salts of acids or hydrohalic acids, bases are well determined so that after subtraction of the alkali metal, halogen limit conductivities to determine the boundary conductivities of anions and cations are also of very weak dissociated particles is possible.

The concentration dependence of the equivalent conductivity Λ is attributed to two effects:

Was Improves theory of Ostwald by the Debye- Hückel law.