An Overview of Ionic Equilibrium Calculation

The majority of chemical reactions take place in solutions, which are formed when a particular component is dissolved in a solvent such as water. In an ionic solution, the substance dissolves into ions; in a molecular solution, the substance remains intact. There are two categories of substances: nonelectrolytes and electrolytes. Electrolytes conduct electricity when they are in aqueous solution or when they are molten. In aqueous solution or molten state, nonelectrolytes do not conduct electricity.

Electrolytes are substances that create ions in their solutions when dissolved in water. When an electric field is applied, these ions are free to move and can conduct electricity through the solution. As a result, such solutions are excellent conductors of electricity. Thus, electrolytes are substances whose solutions are electrically conductive.

Numerous electrolytes are practically fully transformed to ions when dissolved in water. These are referred to as powerful electrolytes. All ionic compounds such as NaCl, KCl, KNO₃, and NH₄Cl, as well as some colloidal compounds such as HCl, are strong electrolytes. The creation of ions (ionisation or dissociation) is depicted in their instance by a single arrow.

NaCl(aq) →Na⁺ (aq)+ Cl^– (aq)

HCl(g) +H₂O(l) →H₃O⁺(aq)+ Cl^– (aq)

On the other hand, a large number of electrolytes are only partially ionised. These electrolytes are referred to as weak electrolytes. Numerous covalent compounds, such as CH3COOH, NH4OH, and C6H5NH2, are electrophiles. In solution, such a chemical exists in two states: unionised molecule form and ion form. When the rate of ionisation of molecules to form ions equals the rate of combining of ions to form molecules, a dynamic equilibrium between the two forms is established. Ionic equilibrium refers to an equilibrium involving ions. ‘Reversible arrows’ depict the equilibrium between unionised molecules and ions. For instance:

CH₃COOH(l)+ H₂O(l) ↔ H₃O⁺ (aq) + CH₃COO^– (aq)

The degree to which a weak electrolyte ionises is denoted by its degree of ionisation, It is defined as the fraction or percentage of the electrolyte’s total amount (or concentration) that exists in the form of ions.

Ionic Equilibrium

Because reactants and products coexist in equilibrium, the conversion of reactants to products is never more than 100%. Equilibrium reactions may involve the decomposition of a covalent (non-polar) reactant or the ionisation of ionic molecules in polar fluids. This section will introduce us to the concept of ionic equilibrium in ionic solutions. Substances in Ionic Equilibrium can be classified into two groups according to their electrical conductivity, as seen below.

• Non-Electrolytes are molecules that do not have an electric charge, do not dissolve into constituent ions, and thus do not conduct electricity in aqueous solution or molten state. Consider the sugar solution as an example.
• Electrolytes are substances that dissolve into constituent ions in water and so conduct electricity in water or molten states. For example, salt solutions, acid solutions, and base solutions. In ionic equilibrium, there are two types of electrolytes: strong and weak electrolytes.

When dissociated in an ionic solution, strong electrolytes completely ionise, whereas weak electrolytes only partially ionise. NaCl, for example, undergoes complete ionisation in water to form sodium ions (Na⁺) and chloride (Cl^–) ions, whereas acetic acid undergoes partial ionisation to form some acetate ions (CH³COO^–) and hydrogen (H⁺) ions. When a strong electrolyte is used, the dissociation reaction is considered to be complete and irreversible, whereas when a weak electrolyte is used, the reaction is said to be reversible. A weak electrolyte achieves ionic equilibrium between the ions and the unionised molecules, which is referred to as ionic equilibrium.

Ostwald’s Dilution Law: Degree of Dissociation

Ostwald’s dilution law is the application of the law of mass action to weak electrolytes in solution. AB is a binary electrolyte in which the A⁺ and B^– ions are dissociated.

AB ⇌ A⁺ + B^–

• For a very weak electrolyte, since α <<< 1, (1 – α) = 1

K=(KV)^1/2

• Concentration of any ion = Cα = √CK. Dilution results in an increase in the level of ionisation. As a result, the extent to which an electrolyte dissociates is proportional to the square root of the dilution.

Limitations of Ostwald’s Dilution law: The law holds true only for weak electrolytes and fails completely in the presence of high electrolytes.

Ionic Equilibrium Formulas

At equilibrium, it is critical to determine the fraction of reactants transformed to products. The degree of dissociation/ionization refers to the proportion of initial molecules that undergo equilibrium transformation.

• Dissociation or ionisation degree = α = (At the start, the number of dissociated reactant molecules) / (At the start, the number of reactant molecules)
• The degree of dissociation in ionic equilibrium can be expressed as a percentage.

% Degree of dissociation or ionization = α = (The number of dissociated or ionised reactant molecules at the commencement of the reaction.) / (At the outset, the reactant molecule count) x100

Factors Influencing the Degree of Dissociation

The degree of dissociation of an electrolyte is determined by the following factors:

• Nature of Solute: Mineral acids, alkalies, and the majority of salts ionise virtually exclusively in water. These are what are referred to as strong electrolytes. On the other hand, organic acids and bases, as well as some inorganic acids and bases such as HCN and NH₄OH, ionise to a lower extent. These are referred to as insufficient electrolytes.
• The Solvent’s Nature: Water’s high dielectric constant (i.e., insulating power) results in greater ionisation than alcohol’s low dielectric constant. For instance, an aqueous solution of hydrochloric acid conducts electricity swiftly, whereas its solution in toluene (an organic solvent) conducts electricity very slowly, owing to the fact that few or no ions are formed in the latter case.
• Dilution: The more solvent used; the more ionisation is caused. As a result, dilute solutions have a higher degree of ionisation than concentrated ones.
• Temperature: As the temperature rises, ionisation increases.
• Other Substances in Solution: Additional electrolytes containing the same ion have an effect on the degree of ionisation of a single electrolyte. The presence of ammonium chloride in a solution, for example, inhibits the ionisation of ammonium hydroxide. The common ion effect refers to the decrease in the degree of ionisation of one electrolyte when another electrolyte containing a common ion is added.

Conclusion

Ionic equilibrium refers to the state of equilibrium between unionised molecules and ions in a solution containing weak electrolytes.

Electrolytes are chemical compounds that conduct electricity in their aqueous or molten states. At any given temperature, the product of hydrogen and hydroxyl ion concentrations is constant in pure water or an aqueous solution. This is referred to as the ionic product of water and is commonly denoted by the unit Kw.