Common Ion Effect
| Also Known As | Common ion effect, ion suppression effect, common-ion equilibrium shift |
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What is Common Ion Effect?
The common ion effect is the decrease in solubility of a sparingly soluble salt when a solution already containing one of its ions is added. For example, the solubility of AgCl decreases when NaCl (a source of Cl⁻) is added, because the equilibrium Ag⁺ + Cl⁻ ⇌ AgCl(s) shifts left. This principle is an application of Le Châtelier's principle.
Properties & Characteristics
Uses & Applications
Safety Information
Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.
Key Facts
Frequently Asked Questions
The common ion effect is the decrease in solubility of a sparingly soluble salt when a solution already containing one of its ions is added. For example, the solubility of AgCl decreases when NaCl (a source of Cl⁻) is added, because the equilibrium Ag⁺ + Cl⁻ ⇌ AgCl(s) shifts left. This principle is an application of Le Châtelier's principle.
The common ion effect is exploited in gravimetric analysis (complete precipitation of an ion by adding excess precipitating agent), in controlling the pH of buffer solutions, in pharmaceutical formulation to control drug solubility, and in water treatment (softening by lime-soda process).
Adding a common ion source to a solution may cause sudden precipitation of sparingly soluble salts. In plumbing and industrial processes, unexpected precipitation can cause blockages. Fluoride added to dental products exploits the common ion effect to reduce calcium phosphate dissolution from teeth.