Factors Affecting Solubility

The solubility of an ionic compound can vary depending on other solutes present in the solution. The solute may be an ion common to the compound, or an acid or base. Thus, two major factors affecting the solubility are the common ion effect and the pH of a solution.

If lead(II) chloride is added to a solution of sodium chloride, both salts will ionize in the water, producing sodium and lead cations and the common anion, chloride.

Because the chloride ions in solution come from both the complete ionization of sodium chloride and the partial ionization of lead(II) chloride, their concentration would be higher than that of either the sodium ions or the lead ions.

To compensate, the equilibrium between the solid lead(II) chloride and its ions in solution shifts towards the undissociated salt, causing more lead(II) chloride to remain undissolved.

Thus, the presence of a common ion decreases the solubility of a sparingly soluble substance.

For instance, the molar solubility, x, of lead(II) chloride in a 0.100 molar sodium chloride solution can be calculated from the ICE table.

The initial concentration of lead(II) ions in the solution is zero, while chloride is 0.100 molar.

Each molecule