what do you understand by common ion effect

The common ion effect is the decrease in solubility or ionization of a weak electrolyte when a substance containing one of its ions is added to the solution. It happens because the extra “common ion” shifts the equilibrium backward, in line with Le Chatelier’s principle.

Quick meaning

If a solution already contains an ion, adding more of that same ion makes the dissolved substance ionize less or precipitate more. This is why the effect is important in solubility , buffer solutions , and salt precipitation.

Simple example

If you add sodium chloride to a solution that already contains chloride ions , the chloride concentration increases, so a salt like silver chloride becomes less soluble and may precipitate more easily. In weak acids or weak bases, the added common ion suppresses dissociation.

One-line definition

Common ion effect = suppression of ionization or solubility due to addition of an ion already present in the equilibrium system.

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