What is Ionic Equilibrium? 

Chemical equilibrium and ionic equilibrium are two major concepts in chemistry. Ionic equilibrium deals with the equilibrium involved in an ionization process while chemical equilibrium deals with the equilibrium during a chemical change. Ionic equilibrium is established between the ions and unionized species in a system. Understanding the concept of ionic equilibrium is very important to answer the questions related to certain chemical reactions in chemistry.

Types of Electrolytes


They are the kind of compounds that do not separate into constituent ions when dissolved. They are comprised of particles that do not possess any electrical charges, simply they do not possess ions. Thus, in a dissolved state, they do not attribute any kind of charge to the solution. Sugar is dissolved in water is a perfect example.


They are the compounds which will separate into constituent ions in a dissolved state. These kinds of compounds are constituted of positive and negative ions (cations and anions respectively). Thus, they can contribute charge to the solution and can thereby conduct electricity. Salt (sodium chloride) dissolved in water is a perfect example of this.

Electrolytes in the context of ionic equilibrium can be classified into two types, strong electrolytes, and weak electrolytes.

Strong electrolytes and weak electrolytes

They can undergo a complete ionization when dissolved. On the other hand, weak electrolytes are those which only undergo a partial ionization or incomplete ionization when dissolved.

For instance, Sodium chloride NaCl undergoes complete dissociation in to sodium Na + and chloride Cl - ions, when dissolved in water. While acetic acid undergoes only fractional dissociation into acetate ions CH 3 COO - and hydrogen H + ions, when dissolved in water.

In the case of strong electrolytes, the dissolution is in the forward direction and will complete rapidly. While in the case of weak electrolytes, going in the forward direction is not that simple. The dissolution reaches equilibrium as time proceeds where an equilibrium between the ionized and unionized compound develops and this is referred as ionic equilibrium.

The equivalent can be perceived with the accompanying model.

"stages of equilibrium (physical)"

Solubility and Solubility Product

The ability of a solute to dissolve in a solvent and form a solution is known as solubility. Ionic compounds which dissociate to form cations and anions have a wide range of solubility in water. Some compounds are extremely soluble and others are extremely insoluble.

The equilibrium constant for the dissolution of solid material into an aqueous solution is the solubility product constant (Ksp). The solubility product is a type of equilibrium constant whose value is temperature-dependent. It normally rises as the temperature rises due to increased solubility. 

Ostwald's Dilution Law

Ostwald's dilution law relates the weak electrolyte's dissociation constant to the degree of dissociation and the concentration of the weak electrolyte.

This law is applicable only in the case of weak electrolytes and it seems to fail when applied to strong electrolytes.

Introducing dissociation constant

It gets important to understand what part of the underlying reactants are changed over into products.

The small portion of the underlying atoms that are changed over at the reaction proceeds is known as the level of dissociation/ionization.

Level of separation or dissociation = α = (Number of reactant atoms dissociatedionized toward the beginning)/(Number of reactant particles toward the beginning)

% Degree of separation or ionization = α = (Number of reactant particles separated or ionized toward the beginning)/(Number of reactant atoms toward the beginning) × 100

"ionic equilibrium"

Level of Ionization

"Level of ionization"

The extent of ionization of a given electrolyte depends on the following factors:

  • Nature of the electrolyte: There are three kinds of electrolytes strong, weak, and insoluble. The ionization extent of strong electrolytes will be grater than that of weak electrolytes. The insoluble electrolytes will not ionize in solution.
  • Nature of the dissolvable: The dielectric constant of the solvent can also affect ionization. A solvent with a higher dielectric constant will enhance ionization.
  • Weakening of the bond: Greater the weakening of the bonds, higher is the ionization.
  • Temperature: As the temperature increases ionization also increases.

Ionization of Weak Electrolytes

All electrolytes are completely ionized during infinite dilution. Powerless electrolytes co-exist with their unionized molecules in a concentrated solution. Particle groupings are essential in a variety of functional situations, such as corrosive base solubility and arrangement conductance.

Common Ion Effect on Degree of Dissociation

In a watery state, weak electrolytes are insufficiently ionized. One of the off chance could be that one of the particles is accessible from another source then their ionization could be reduced as well. This is referred to as a common ion effect. Examples include:

  • Ammonium hydroxide is a weak base: When ammonium chloride is added to ammonium hydroxide, the ammonium ions in it will approach hydroxide ions to form ammonium hydroxide back.
  • Manufacture of sodium bicarbonate: In the Solvay soft drink scale, to extract sodium bicarbonate, CO 2 gas is passed through an ammoniacal saline solution.

NaHCO 3 is accelerated first on account of its lower solvency item when contrasted with those of NH 4 Cl, NH 4 HCO 3  and NaCl.

Solid Electrolytes

Electrolytes that separate totally into constituent particles in the fluid arrangement are known as solid electrolytes. e.g. all salts (aside from NH 4 Cl, NH 4 HCO 3  and NaCl. Mineral acids like HCl, H 2 )SO 4 , HNO 3 , and so forth and bases like NaOH. KOHand so on.

Frail Electrolytes

Electrolytes which separate less significantly in the watery arrangement are called a powerless electrolyte. Every natural corrosive (with the exception of sulphonic acids), and bases like NH 3 . NH 4 OH, amines, and so forth.

Context and Applications  

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for Bachelors and Masters in Chemistry.

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