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| 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 '''common-ion effect''' is a term used to describe the effect on a solution of two dissolved solutes that contain the same ion. | ||
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| *If both ] and ] are dissolved in the same solution they both dissociate and ionize to produce ]s. Sodium acetate is a ] so it dissociates completely in solution. Acetic acid is a ] so it only ionizes slightly. According to ], the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its ] to the left. | *If both ] and ] are dissolved in the same solution they both dissociate and ionize to produce ]s. Sodium acetate is a ] so it dissociates completely in solution. Acetic acid is a ] so it only ionizes slightly. According to ], the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its ] to the left. | ||
| :NaC<sub>2</sub>H<sub>3</sub>O<sub>2</sub><sub>(s)</sub> |
: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> |
: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. | This will decrease the hydrogen ion concentration and thus the common-ion solution will be less acidic than a solution containing only acetic acid. | ||
Revision as of 05:51, 18 September 2006
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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 ions. 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 equilibrium to the left.
- 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.