• The common ion effect is a decrease in the solubility of an ionic compound as a result of the addition of a common ion.
  • A common ion is an ion that is in common to both salts in a solution.
  • Adding calcium nitrate to a saturated solution of calcium sulfate causes additional CaSO4 to precipitate from the solution, lowering itssolubility.
  • Adding potassium sulfate to the same saturated solution would result in the same effect.Calculations involving the common ions effect are described.
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