Question

In absence of formation of complex ions by the addition of a common ion, the solubility of $PbC{l_2}$ ​
A. Increases
B. Decreases
C. Unaffected
D. First increases and then decreases

Answer 1

Hint: While solving this type of question we should have a knowledge of common ion effects. The common ion effect is a phenomenon whereby the presence of another electrolyte suppresses the ionisation of one electrolyte. Principle of Le-Chateliers is also used here.

Complete Step by Step Solution:
Technically speaking, the common ion effect is when we introduce another species containing the same ion to an existing solution in which equilibrium has already been reached, we see a reduction in the degree of dissociation of the first species.
Naturally, the concentration of chlorine will increase if we add sodium chloride to this. This extra chlorine will cause the equilibrium to move to the left, causing more $PbC{l_2}$ to form.

If a solution and solute are in equilibrium, introducing a common ion—an ion that shares a common ion with the solid that is dissolving—reduces the solubility of the solute. This is so that the excess product's tension can be relieved, according to Le Chatelier's principle, which states that the reaction will move to the left (i.e., toward the reactants).

Additional information: Le Chatelier's principle for the equilibrium response of ionic association or dissociation results in the common ion effect. The solubility of a chemical is also influenced by the common ion effect. However, this tendency can also be used to your benefit. Chalk and limestone-containing aquifers are employed in these to produce drinking water because they have a common ion impact. Due to its limited solubility in water, calcium carbonate can be precipitated out of a solution by adding sodium chloride. In this manner, water treatment makes use of the common ion effect.

Note: Due to their tendency to produce complex ions, compounds of transition metal ions do not exhibit common ion effects. Also note that a precipitation reaction will take place.