Common-ion effect 338192 210722088 2008-05-07T02:52:31Z 166.104.205.35 /* Examples */ 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]]. ==Examples== *If both [[sodium acetate]] and [[acetic acid]] are dissolved in the same solution they both dissociate and ionize to produce [[acetate ion]]s. Sodium acetate is a [[strong electrolyte]] so it dissociates completely in solution. Acetic acid is a [[weak acid]] so it only ionizes slightly. According to [[Le Chatelier's principle]], the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its [[chemical equilibrium|equilibrium]] to the left. Thus the percent dissociation of the acetic acid will decrease and the pH of the solution will increase. :NaC<sub>2</sub>H<sub>3</sub>O<sub>2</sub><sub>(s)</sub> → Na<sup>+</sup><sub>(aq)</sub> + C<sub>2</sub>H<sub>3</sub>O<sub>2</sub><sup>-</sup><sub>(aq)</sub> :HC<sub>2</sub>H<sub>3</sub>O<sub>2</sub><sub>(l)</sub> ↔ H<sup>+</sup><sub>(aq)</sub> + C<sub>2</sub>H<sub>3</sub>O<sub>2</sub><sup>-</sup><sub>(aq)</sub> 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" == See also == *[[Buffer solution]] *[[Solubility]] *[[Solubility equilibrium]] [[Category:Ions]] [[Category:Physical chemistry]] [[it:Effetto ione comune]] [[zh:同离子效应]]