How to Calculate Molarity

To calculate the Molarity of a chemical Compound, you must understand the meaning of Molarity, Concentration, and Molar mass. Understanding the meanings involves knowing their units of measurement and the relationships between those units.

Calculations in experimental Acid-Base Titration sometimes requires the calculation of the molarity of the reactants and or the products. Though the unknown concentration of a reactant can be calculated from the known volume of acid and base in the reaction, and the concentration of one of the reactants, the concentration of the products are obtainable with a good knowledge of the calculation of Molarity.

The Molar mass of a chemical compound is the sum of the proportion of the relative atomic masses of all the elements in that compound. The unit of measurement is in g/Mol or gMol^-1. The Molar mass of a chemical compound in a chemical reaction is affected by the number of moles of that compound in the reaction. The number of moles of a compound is equal to 1 if the compound in question do not have number of moles attached to it e.g the number of mole of H₂SO₄ in the chemical reaction

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O is 1 while that of NaOH is 2.

Concentration of a chemical compound can be represented in terms of moles or gram contribution. But the perception of Concentration is usually in grams. For example, the unit of concentration is mostly represented as gdm^-3 even though it is also moldm^-3 if the measurement is in Moles.

Molarity is simply Concentration. It is Concentration in Mol/dm³ or Moldm^-3. Molarity of a chemical compound is calculated from the molar mass and the concentration in g/dm³ of that compound as follows:

Molarity = Concentration in g/dm³/Molar mass. This can be expressed in the unit of measurement as,

Molarity = gdm^-3 /gMol^-3 = Moldm^-3.

Hence, Concentration in gMol^-3 will be equal to Molarity multiplied by molar mass. And molar mass will be concentration in gMol^-3 divided by concentration in Moldm^-3 which is equal tp gMol^-1.