COMMON ION EFFECT

by • 27/08/2013 • GeneralComments (0)597

COMMON ION EFFECT

 

Definition

A phenomenon in which the solubility of weak electrolytes decreases due to the addition of strong electrolyte with common ion in the same solution is called common ion effect.

Explanation With Example (Application Of Common Ion Effect)

An electrolyte is precipitated from its solution only when the concentration of its ions exceeds from the solubility product. The precipitates are obtained when even the concentration of any one ion is increased. Thus by adding the common ion, the solubility product can be exceeded.

Consider a solution of Silver Chloride which is a weak electrolyte and dissociates in the aqueous solution as,

AgCl === Ag+ + Cl-

After some time the dissociation of Silver Chloride reached at equilibrium.

Effect of positive ion:

If Sodium Chloride which is a strong electrolyte added in the same solution which dissociates as:

NaCl === Na+ + Cl-

Due to the addition of Sodium Chloride the concentration of Na* increase in the solution so that the equilibrium of dissociation of Silver Chloride disturbed in order to regain equilibrium reaction moves in reverse direction to form undissolved Silver Chloride so that its solubility decreases.

Effect of positive ion:

Similarly if Silver Nitrate which is a strong electrolyte added in the same solution which dissociates as:

AgNO3 === Ag+ + NO3‾

Due to the addition of Silver Nitrate the concentration of Ag* increase in the solution so that the equilibrium of dissociation of Silver Chloride disturbed in order to regain equilibrium reaction moves in reverse direction to form undissolved Silver Chloride so that its solubility decreases.

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