Question

Which best demonstrates an example of the common ion effect?

Answer 1

Answer: A.  The compound CuCl is 500 times less soluble in sea water than it is in pure water.

pure water.

Explanation:

Any change in the equilibrium is studied on the basis of Le-Chatelier's principle.

This principle states that if there is any change in a equilibrium reaction, the equilibrium will shift in a direction so as to minimize the effect.

Thus when a common ion is introduced to an equilibrium reaction, the equilibrium will shift in a direction where the concentration of common ion is decreasing.

$CuCl\rightleftharpoons Cu^++Cl^-$

$NaCl\rightarrow Na^++Cl^-$

When common ion such as $Cl^-$ from NaCl in sea water is introduced to an equilibrium reaction, the equilibrium will shift in a direction where the concentration of common ion is decreasing i.e. in the left side and thus solubility of CuCl further decreases.