What is Normality of a solution ? How to Calculate it ?

The normality of a solution is defined as the equivalent gram weight of any solute per liter of solution. It may also be known as the equivalent concentration. It is denoted by the symbol ‘N’. A gram equivalent weight or equivalent measures the reaction capacity of ion, molecule, etc. The equivalent value is calculated by the molecular weight and valence of that chemical species. Normality is a concentration unit that is reaction dependent.

Normality is a unit of concentration in which a chemical solution is expressed as gram equivalent weight of solute per litre of solution. An equivalence factor is used to express the concentration. Units of normality are ‘N’, ‘equivalent/L‘, or ‘milliequivalent/L‘.

Normality is a unit that depends on the chemical reaction which is being examined. The use of Normality is not appropriate for all chemical solutions. Normality is generally used in acid-base chemistryredox reactions, or precipitation reactions. Molarity or molality are more often used for units.

Also Read: Differences Between Alkali and Alkaline

There are certain situations where we prefer to use Normality rather than molarity or any other unit of concentration of a chemical solution. Normality is used in acid-base reactions to evaluate the concentration of ‘Hydronium’ (H3O+) ion and ‘Hydroxide’ (OH-) ion. Here, in this case, 1/feq is the integer part.

The equivalence factor.e; Normality is used in precipitation reactions to define the number of ions that is going to precipitate. Here, 1/feq is once again an integer value. In redox reactions, Normality indicates how many electrons can be donated or accepted by an oxidizing or reducing agent. For redox reactions, 1/feq may also be a fraction.

Also Read: Facts about Acids and Bases- Chemistry.

The unit of Normality is not appropriate for concentration in every situation. It requires a defined equivalence factor. Normality is not a constant value for any chemical solution; instead, it is variable. The value of normality changes according to the chemical reaction, being examined.

The normality Formula is used to measure the concentration of a solution. It is the equivalent concentration of a solution. It measures the reactive species in a solution and also during titration reactions. Gram equivalent weight is determined by the amount of an ion that reacts. But this also varies depending on the reaction.

Normality can also be described as the number of grams of mole equivalents of solute present in one litre of a solution. Normality is mainly used to determine the concentrations in acid-base chemistry, in precipitation reactions to evaluate the number of ions precipitated in any given reaction, and in redox reactions to calculate the number of electrons of any reducing or oxidizing agent.        

Normality Formula

Normality (N) = Number of equivalent gram volume of the solution in litres.

Where Number of gram equivalent =Weight of solute × Equivalent weight of solute.

Hence N= Weight of Solute(gram) ×Equivalent weight × Volume(in litre)

We can also calculate it using Molarity as:

N = Molarity × Molar mass ×Equivalent mass

N = Molarity × Basicity = Molarity × Acidity

To sum up, the calculation of Normality involves- Finding the information about the equivalent weight of the reacting substance or the solute, then finding out the number of gram equivalent of solute by calculation, then calculating the volume in litres. Then calculate Normality using its formula.

We express Normality as eq/L, i.e. equivalent per litre.

In a titration, the equation of Normality is- N1 V1 = N2 V2

Where N1 is the Normality of the acidic solution, V1 is the Volume of the acidic solution, N2 is the Normality of the basic solution, and V3 is the Volume of the basic solution. The equation of Normality used to estimate the volume of a solution of different Normality is:

Initial Normality (N1) × Initial Volume (V1) = Normality of the Final Solution (N2) × Final Volume (V2).

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