The Common Ion Effect

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The Common Ion Effect

The concentrations of ions in solution are affected by all equilibria and all species present in the solution. The simplest and most significant such effect is called the common ion effect. The common ion effect is observed whenever an ion in solution is common to two different salts which serve as its sources. Addition of the second salt adds the common ion, which is a product of the dissolution of the first. The effect of adding the product ion will be to decrease the solubility of the first salt.
If a salt M1xA1y (e.g. BaF2 : x=1, y=2) is added into a solution already containing a common ion e.g. M2+m (Ba+2), the expression for the solubility product will be:
Ksp=[M1+m+M2+m]x [A1-a]y

Solubility Product

Solubility In Water

Solubility Rules

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