The Importance of Common Ion Effect

The solubility products Ksp’s are equilibrium constants in heterogeneous equilibria (i.e., between two different phases) (i.e., between two different phases). If several salts are present in a system, they all ionise in the solution. If the salts contain a common cation or anion, these salts contribute to the concentration of the common ion. Contributions from all salts must be included in the calculation of concentration of the common ion. For example, a solution containing sodium chloride and potassium chloride will have the following relationship:

Solubility

The term “solubility” refers to the amount of material that can be dissolved in a given amount of a given solvent. For example, when table salt (NaCl) is placed in water, it will dissolve eventually. More table salt, on the other hand, will continue to be added indefinitely until the solution reaches a point where no more can be dissolved; in other words, the solution will become saturated, and the table salt will have effectively reached its solubility limit.

When there are no net physical or chemical changes between the reactant and the products of a reaction, this is referred to as chemical equilibrium, and it exists in nature. In this case, this is due to an equal rate of forward (from reactant to product) and reverse (from product to reactant) reactions taking place.

The term “solubility equilibrium” refers to the state of chemical equilibrium between a chemical compound in the solid state and a solution containing that chemical compound dissolved in water. Equilibrium is achieved when the rates of migration between the solid and aqueous phases of the molecules (or ions) are equal in both directions.

The Influence on Solubility

This subsection discusses the effect that the presence of a common ion has on the solubility of a salt in a solution.

In aquifers (underground layers of water mixed with permeable rocks or other unconsolidated materials), such as those containing chalk or limestone, the common ion effect can be used to obtain drinking water. The addition of sodium carbonate (chemical formula Na2CO3) to water has the effect of lowering the hardness of the water’s composition.

By adding sodium carbonate to water, which is highly soluble, the common ion effect can be used to precipitate out the calcium carbonate (which is only sparingly soluble) from the water, which is then filtered out.

Sodium carbonate is used to precipitate calcium carbonate, which results in a finely divided calcium carbonate precipitate with a very pure composition. In this way, the CaCO3 precipitate is a valuable by-product of the toothpaste manufacturing process, and it can be used to make other products.

The common ion effect can be observed in the salting-out process, which is used in the manufacture of soaps, because soaps are the sodium salts of carboxylic acids that contain a long aliphatic chain (fatty acids). It is necessary to reduce the solubility of the soaps before they can be precipitated out. Sodium chloride is added to the soap solution to accomplish this.

The presence of significant amounts of sodium ions in water, such as seawater and brackish water, can, however, impair the action of soaps by decreasing their solubility and, consequently, their effectiveness. Seawater and brackish water are examples of such water.

pH and the Common-Ion Effect are two important concepts in chemistry.

The common ion effect causes the pH of a buffer solution to change when the conjugate ion of a buffer solution (solution containing a base and its conjugate acid, or an acid and its conjugate base) is added to it. When the conjugate ion of a buffer solution is added to it, the pH of the buffer solution changes.

In one instance, when acetic acid and sodium acetate are both dissolved in a given solution, the formation of acetate ions can be observed as a result of the reaction. Sodium acetate, on the other hand, completely dissociates, whereas acetic acid only partially ionises. This is due to the fact that acetic acid is a weak acid and sodium acetate is a strong electrolyte, respectively.

Sodium acetate, according to Le Chatelier’s principle, produces new acetate ions that aid in the suppression of the ionisation of acetic acid, thereby shifting the equilibrium to the left. Due to a decrease in the rate of acetic acid dissociation, a rise in the pH of the solution is observed.

Consequently, the pH of the common ion solution containing acetic acid and sodium acetate will be higher and, as a result, less acidic when compared to the pH of acetic acid solution.

Conclusion

The common ion effect is an effect that occurs when an electrolyte is mixed with another electrolyte that contains an ion that is also present in the first electrolyte, i.e. a common ion, and the ionisation of the first electrolyte is suppressed. As a result of Le Chatelier’s principle, it is considered to be a natural consequence (or the Equilibrium Law).