What are molarity, molality, and normality? Explain with an example.

By Ritesh|Updated : November 11th, 2022

The molarity of a solution is a weight-by-volume relationship to represent its strength and is defined as 'the number of moles of solute dissolved in one liter of solution. Molality (m) is defined as the number of moles of the solute per kilogram (kg) of the solvent. Normality is the measure of concentration equal to the gram-equivalent mass of a substance per liter of solution.

Examples of Molarity, Molality and Normality

Molarity:

The number of moles of solute dissolved in one litre of solution is known as the molarity of the solution, which is a weight-to-volume relationship used to represent the strength of a solution.

Molarity formula: Molarity = moles of solute/ volume of solution in litre

Example of Molarity:

1.25 mol L-1 or (1.25 M) solution of KOH means that 1.25 mol of KOH has been dissolved in one litre (or one cubic decimetre).

Molality:

The amount of moles of the solute per kilogramme (kg) of the solvent is known as molality (m).

The molality formula can be written as Molality = moles of solute/ mass of solvent in kg

An example of molality is provided below:

1 mol kg-1 (or 1m) solution of KCl means that 1 mol (74.5 g) of KCl is dissolved in 1 kg of water.

Normality:

It is a unit of concentration that is equal to the mass of a material in grammes per litre of solution.

Normality formula: Normality = number of gram equivalents of solute/ volume of solvent in litre

An example of normality is provided below:

1N HCl solution is one Molar HCl solution because only 1 mole of H+ is formed per mole of HCl.

Summary:

What are molarity, molality, and normality? Explain with an example.

The number of moles of solute dissolved in one litre of solution is known as the molarity of the solution, which is a weight-to-volume relationship used to represent the strength of a solution. The amount of moles of the solute per kilogramme (kg) of the solvent is known as molality (m). The gramme equivalent mass of a material per litre of solution is used to calculate normality, which is a measure of concentration.

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