Chemistry 102: Solubility: word problem explanation needed

Question

1. Suppression of the solubility of one ion by the addition of the counter-ion in its insoluble salt is known as the ___

[common-ion effect].

Explain why the answer is [common-ion effect]

Answer 1

It is called the "common ion effect" because when one of the ions of the insoluble salt is also present in solution, it will reduce the solubility of the already insoluble salt based on LeChatelier's principle. This can be illustrated with an example as follows:

Take the insoluble salt AgCl.

AgCl(s) <==> Ag⁺(aq) + C^l-(aq)

If you now have a common ion present (say Cl- for example in the form of NaCl), the increased concentration of Cl- will push the above reaction to the left (toward reactant) and thus back toward the AgCl(s) form, thus reducing the solubility.