ABSE_Common Ion Effect Lesson

Common Ion Effect

A salt is less soluble if the soluble if the solvent already contains an ion of the salt. And if a common ion is added to an already saturated solution, crystals will form as some of the salt comes out of solution. Watch this to see a sample problem and an explanation of the common ion effect.

Remember that when you set up your ice chart, first look at the composition of the solvent into which the salt will be placed. A problem won't specifically say that it is a common ion problem. So you will need to look for this yourself. Ask yourself, does it contain any of the ions involved in the equilibrium? If it doesn't, the initial concentrations will be set equal to zero. However, if the solvent contains a solute that is a source of one of the ions in the equilibrium, you will use its concentration as the initial concentration of that ion.

Precipitation

image of precipitateOften a solution will be prepared with several sources of ions mixed together. It is important to know if any of the ions will combine to produce an insoluble product. When that happens, a precipitate might form. It depends on the ion product of the ions involved and the value of Ksp. By comparing the ion product to Ksp you can determine whether or not a precipitate will form.

ion product > Ksp supersaturated solution precipitate will form ion product = Ksp supersaturated solution saturated solution precipitate will form precipitate will not form ion product < Ksp unsaturated solution saturated solution precipitate will form

Use this presentation to learn how to determine whether a precipitate will form.

Remember to work on the module practice problems as you complete each section of content.  

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