Common-ion effect - Citizendia

The common-ion effect is a term used to describe the effect on a solution of two dissolved solutes that contain the same ion.

The presence of a common ion suppresses the ionization of a weak acid or a weak base. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons A weak acid is an Acid that does not completely donate all of its hydrogens when dissolved in water In chemistry a weak base is a Chemical base that does not Ionize fully in an Aqueous solution.

Examples

If both sodium acetate and acetic acid are dissolved in the same solution they both dissociate and ionize to produce acetate ions. Sodium acetate, (also sodium ethanoate) is the Sodium salt of Acetic acid. Acetic acid, also known as ethanoic acid, is an organic chemical compound, giving Vinegar its sour taste An acetate, or ethanoate, is either a salt or Ester of Acetic acid. Sodium acetate is a strong electrolyte so it dissociates completely in solution. A strong electrolyte is a Solute that completely or almost completely ionizes or Dissociates in a solution Acetic acid is a weak acid so it only ionizes slightly. A weak acid is an Acid that does not completely donate all of its hydrogens when dissolved in water According to Le Chatelier's principle, the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its equilibrium to the left. In Chemistry, Le Chatelier's Principle, also called the Le Chatelier-Braun principle, can be used to predict the effect of a change in conditions on a Chemical In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change Thus the percent dissociation of the acetic acid will decrease and the pH of the solution will increase.

NaC₂H₃O₂_(s) → Na⁺_(aq) + C₂H₃O₂^-_(aq)

HC₂H₃O₂_(l) ↔ H⁺_(aq) + C₂H₃O₂^-_(aq)

This will decrease the hydrogen ion concentration and thus the common-ion solution will be less acidic than a solution containing only acetic acid.

"A salt will be less soluble if one of its constituent ions is already present in the solution"

Examples

See also