Common Ion Effect: Important Topic Of Chemistry

What is common ion effect? What does it refer to? How is common ion effect related to Le Chatelier’s principle? This article shall answer the above questions while providing all the related information. Let us get started.

Common ion effect definition

Adding a soluble compound that shares an ion with a precipitate reduces the solubility of the precipitate, which is known as the common-ion effect. This behavior is a result of Le Chatelier’s principle for the ionic association/dissociation equilibrium reaction. Increasing the concentration of one of the salt’s ions causes the solubility of salts and other weak electrolytes to decrease, leading to increased precipitation and the eventual reaching of the salt’s solubility equilibrium. The presence of both the original salt and a second additional chemical with a shared ion causes this effect.

A brief outline

The role of the common ion effect in solutions is most obvious in the reduction of solid solubility. Because of a shift in equilibrium, the solubility of a chemical drops when common ions are added. The common ion effect is also involved in buffer management. An acid or base is present in buffering solutions, along with its conjugate counterpart. The pH of the solution will eventually shift as additional similar conjugate ions are added. When evaluating solution equilibrium after adding ions that are already present in the solution, the common ion effect must be taken into account. The common-ion effects are beneficial to the salting-out procedure used in soap production. Soaps are fatty acid sodium salts. The solubility of the soap salts is reduced when sodium chloride is added. A mixture of common-ion action and higher ionic strength causes the soaps to precipitate.

 

Important concepts of Common ion effect:

When gaseous hydrogen chloride is circulated through a sodium chloride solution, the excess chloride ions in the solution cause the NaCl to precipitate, which is an example of the common ion effect. In transition metal complexes, this effect is not observed. This is due to the d-block elements’ proclivity for forming complexions. Cuprous chloride, which is water-insoluble, is a prime illustration of this. The addition of chloride ions to this molecule causes the CuCl2– complex-ion to form, which is soluble in water.

Solubility Effects

In this article, we’ll look at how the addition of a common ion affects the solubility of a salt in a solution.

1. This effect can be utilized to extract drinking water from chalk or limestone-containing aquifers (underground layers of water combined with porous rocks or other poorly consolidated materials). The hardness of the water is reduced by applying sodium carbonate to it.
2. It is employed in water treatment to precipitate calcium carbonate (which is readily soluble) from the water by adding sodium carbonate (which is highly soluble).
3. This addition of sodium carbonate produces a finely dispersed calcium carbonate precipitate with an extremely pure composition. In conclusion, the CaCO3 precipitate is a desirable by-product that could be used in the manufacturing of toothpaste.
4. Sodium chloride reduces the solubility of the detergent solution and precipitates out the soaps, which are sodium salts of carboxylic acids with a long aliphatic chain (fatty acids), in the salting-out process utilized in the making of soaps.

However, water with a sensible number of Na+ ions, such as saltwater and brackish water, might impede the action of soaps by diminishing their solubility and hence their activity.

The Common-Ion Effect and pH

1. Buffer solution pH changes with introduction of conjugate ion due to common ion effect.”
2. When acetic acid and sodium acetate are both dissolved in the same solution, acetate ions are produced. Sodium acetate, on the other hand, totally dissociates, whereas acetic acid only partially ionizes. Because acetic acid is a weak acid, sodium acetate is a strong electrolyte, this is the case.
3. According to Le Chatelier’s principle, sodium acetate’s new acetate ions aid in the suppression of acetic acid ionization, pushing the equilibrium to the left. Because acetic acid dissociation is minimized, the pH of the solution rises.
4. As an outcome, when contrasted to an acetic acid solution, the common ion solution comprising acetic acid and sodium acetate will also have a higher pH and so be less acidic.

Also read: Important Topic Of Chemistry: Degree of Ionization

FAQs

Q. What exactly is the common ion effect? Give a specific example.

Ans: The common ion effect is defined as the change in equilibrium caused by the addition of a substance that supplies more ionic species to the dissociation equilibrium. Le Chatelier’s principle describes the common ion effect as a phenomenon.”

Excess chloride ions cause sodium chloride to precipitate due to gaseous hydrogen chloride, demonstrating the common ion effect.”

Q. Is it true that it affects solubility?

Ans: Common ion effect alters solubility when adding salt to a solution. Solubility of salt is influenced by presence of common ion. Solubility is greatly reduced when salt is dissolved in solution with its ion.

Q. Who among the two pairs would have a common ion effect? a) BaCl₂ + Ba (NO₃) b) HCl + NaCl c) NH₄OH + NH₄Cl d) AgCN + KCN

Ans: When weak and strong electrolytes are coupled, the common ion effect takes place.

• Because one is an acid and the other is a salt of a strong acid and a strong base, NaCl and HCl totally dissociate.
• Because one is an acid and the other is a salt of a strong acid and a strong base, AgCN and KCN entirely dissociate.
• NH₄OH is a weak base to which NH₄Cl is added, suppressing the NH4OH’s common NH₄+ion dissociation. Because NH4OH is a weak electrolyte and NH4Cl is a strong electrolyte, the common ion action is seen in this pair.