Mole (chemist secret unit): Definition, Examples and calculation Formula

A mole is defined as the amount (mass) of a substance that contains 6.02 x 10²³  number of particles ( atoms, molecules, or formula units). It establishes a link between the mass of a substance and the number of particles as shown in the summary of molar calculations. It is abbreviated as ‘ mole’.

You know that a substance may be an element or compound ( molecular or ionic). Mass of the substance is either one of the following: atomic mass, molecular mass, or formula mass. These masses are expressed in the atomic mass unit (AMU). But when these masses are expressed in grams, they are called as molar masses.

Scientists have agreed that Avogadro’s number of particles are present in one molar mass of a substance. Thus, the quantitative definition can be defined as the atomic mass, molecular mass, or formula mass of a substance expressed in grams is called the mole.

For example:

The atomic mass of carbon expressed as 12g = 1 mole of carbon

The molecular mass of H₂O expressed as 18g = 1 mole of water

The molecular mass of H₂SO₄ expressed as 98g = 1 mole of H₂SO₄

The formula mass of NaCl expressed as 58.5 g = 1 mole of NaCl

Thus,  the relation between mole and mass can be expressed as:

A detailed relationship between a substance and through molar mass and number of particles is present here.

A summary showing a relationship between a substance and a mole.

Example of the calculation of Moles:

Calculate the gram molecule (number of moles) in 40 g of H₃PO₄.

Solution:

Given the mass of H₃PO₄  = 40 g

Molecular mass of H₃PO₄ = 98 gmol^-1

Putting these values in the equation

Therefore, 40 grams will contain a 0.408-gram molecule (mol) of H₃PO_4.