Ostwald's dilution law states that the degree of dissociation (
) of a weak electrolyte is directly proportional to the square root of its dilution (
) or inversely proportional to the square root of its molar concentration (
). It applies only to weak electrolytes, where
increases with dilution, approaching complete ionization at infinite dilution.

Key Concepts
Definition: The law applies Ostwald's dilution law to weak electrolytes (e.g.,
,
) that partially dissociate in solution.
Core Principle: As the volume (
) of solvent increases (dilution), the degree of dissociation (
) increases, meaning the electrolyte ionizes further.
Formula:

For weak electrolytes,
is very small, so


, simplifying the formula to


, or

.
Since concentration

, this shows

.
Limitations: The law is not applicable to strong electrolytes (like
) which are completely dissociated at all concentrations.

Summary Table
Concept Description
Applicability Weak Acids and Weak Bases
Relation
increases as Concentration decreases
Infinite Dilution

(Complete dissociation)
Expression

This law provides a quantitative relationship between the dissociation constant (
) and the degree of ionization of weak electrolytes.