The Common Ion Effects

When a common ion (an ion already present in the solution) is added to a solution, the common ion effect defines the effect on equilibrium that happens. A solute’s solubility is reduced by the common ion effect. It can also change the pH of buffering solutions by introducing additional conjugate ions.

The equilibrium response of ionic association/dissociation is governed by Le Chatelier’s principle, which explains this behaviour. The effect is most typically recognised as a decrease in the solubility of salts and other weak electrolytes. Increasing the concentration of one of the salt’s ions decreases the concentration of both ions until the solubility equilibrium is attained. The effect is due to the fact that the original salt and the additional chemical share one ion.

Solubility effects

The addition of sodium carbonate to the raw water to lessen the hardness of the water is a practical example extensively employed in locations receiving drinking water from chalk or limestone aquifers. To precipitate out sparingly soluble calcium carbonate, highly soluble sodium carbonate salt is used in the water treatment process. The calcium carbonate precipitate, which is very pure and finely split, is a valuable by-product that is utilised in the production of toothpaste.

The common-ion effect is advantageous to the salting-out procedure used in soap manufacturing. Soaps are fatty acid salts that have sodium sulphate added to them. The solubility of the soap salts is reduced by adding sodium chloride. A combination of the common-ion action and increasing ionic strength causes the soaps to precipitate.

The common-ion effect interferes with the typical behaviour of soap in sea, brackish, and other fluids that include significant amounts of sodium ions (Na+). The solubility of soap salts is lowered in the presence of high Na+, reducing the soap’s effectiveness.

Examples of common ion effect

When sodium chloride (NaCl) is introduced to an HCl and water solution, the common ion effect is demonstrated. After the hydrochloric acid and water have reached equilibrium, the products are H3O+ and Cl-.

HCl + H2O –> H3O+ + Cl–

NaCl makes Na+ + Cl–

Na+ and Cl- are formed when the NaCl dissolves in the solution. The concentration of Cl- ions rises as the sodium chloride dissolves. The system compensates by recombining the Na+ and Cl- to form NaCl, a solid that precipitates out of solution. In effect, more Cl- ions were added to the solution in equilibrium, which pushed the equilibrium back to the left.

The chemical equilibrium of salts and other weak electrolytes, as well as their ions in solutions, is based on Le Chatelier’s Principle. This effect is frequently employed to alter the solubilities of salts and weak electrolytes, as well as precipitate salts from solutions.

When a different salt or electrolyte with one common ion is added to a solution containing an already dissolved salt or electrolyte, the concentration of the common ion increases, causing the dissolved salt or electrolytes equilibrium to shift to the initial salt or electrolyte side, lowering its solubility.

Conclusion 

The solubility equilibrium alters in the way indicated by Le Chatelier’s principle when a common cation or common anion is added to a solution of a sparingly soluble salt. When a common ion is present, the salt’s solubility is almost always diminished.

1. The common ion impact is most obvious in the reduction of solid solubility in solutions. Because of a shift in equilibrium, a compound’s solubility normally drops when common ions are added.
2. In the modulation of buffers, the common ion impact is also important. An acid or base, as well as its conjugate counterpart, are present in buffering solutions. The pH of the solution will eventually change as additional similar conjugate ions are added.
3. When calculating solution equilibrium following the addition of ions already present in the solution, the common ion effect must be taken into account.

The solubility of solutes in a reacting system is affected by the common-ion effect, which is a change in chemical equilibrium. The phenomenon is a regular occurrence in chemistry analysis and industrial research due to the application of Le-principle Chatelier’s for equilibrium reactions. It’s a significant phenomena that may be applied in practice to better understand particular reaction settings that favour greater product production.