Percentage Ionization
Definition and meaning of Percentage Ionization in chemistry.
Percentage ionization is the fraction of a weak acid or weak base that has ionized in aqueous solution, expressed as a percentage. It is a quantitative measure calculated by dividing the concentration of ionized species by the initial concentration of the weak acid or base, then multiplying by 100%.
In more detail
For a weak acid HA, percentage ionization is calculated using the formula [H+]/[HA]0 × 100%, where [HA]0 is the initial concentration of the weak acid. The percentage value depends on both the inherent strength of the acid or base (its Ka or Kb value) and the concentration of the solution. Dilution increases percentage ionization by shifting the ionization equilibrium forward according to Le Chatelier's principle. Understanding percentage ionization is essential for predicting pH values and determining the extent of ionization in weak acid and base solutions.
Key facts
| Calculation | ([H+] / [HA]0) × 100% |
|---|---|
| Applies to | Weak acids and weak bases only |
| Effect of dilution | Percentage ionization increases when solution is diluted |
| Field | Physical Chemistry |
A 0.10 M solution of acetic acid (CH3COOH) has approximately 1.3% ionization, producing about 0.0013 M of H+ ions and acetate ions in solution.
Frequently asked questions
What is the percentage ionization of a strong acid?
Strong acids have approximately 100% ionization because they completely dissociate in aqueous solution, leaving virtually no molecular acid remaining.
How does dilution affect percentage ionization?
Dilution increases percentage ionization. When a weak acid solution is diluted, the equilibrium shifts forward to produce more ions, increasing the fraction of molecules that have ionized.