What is a Mole in Chemistry?

What is a Mole in Chemistry?

What is a mole in chemistry, we express a collection of 6.023 X 10²³  atoms, ions or molecules. We use the word mole to express the amount of a substance (atom, molecule or ion), present as in 12 grams of C-12 atom.

The number of atoms present in C-12 isotope of carbon is 6.023 X 10²³ atoms and we can take it as a base for the mole concept. What is a mole is important for a chemist because it provides a bridge between the atom. Also, it bridges the macroscopic amounts of material useful in the laboratory.

It enables the chemist to weigh out amounts of two substances, say iron and sulfur, such that he obtains equal numbers of atoms of iron and sulfur.

Definition of Mole

“One mole of any substance (atom, molecule, etc.) is equal to its atomic mass or molecular mass expressed in grams. The number of particles present in one mole of any substance ( atom or molecule) is 6.023 X 10²³. Molar mass is the mass in grams of one mole (mol) of a chemical substance.

Generally, the molar mass has units of grams per mole (g/mol). In the case of molecules, the molar mass in grams of one mole of molecules is its molecular mass. In the case of atoms, the molar mass in grams of one mole of atoms is its atomic mass.

Examples Illustrating the Mole Concept

A. 1 mole of hydrogen (H) atom contains 6.023 X 10²³ atoms of hydrogen. The atomic mass of a hydrogen atom is 1.008 grams. So, in terms of the mole concept, we can infer that 1 mole of hydrogen atoms= 1.008 grams hydrogen=6.023 X 10²³ atoms of hydrogen.

B. Take another example of a molecule of carbon dioxide ( CO₂ ) . 1 mole of CO₂  molecule contain 6.023 X 10²³ molecules of CO₂  and the molecular mass of CO₂  is 44 grams. So, in terms of mole concept, we can infer that 1 mole of CO₂ molecule = 44 grams of CO₂ = 6.023 X 10²³ molecules of CO₂. 

The concept can be further extended to draw other inferences.  We know that 44 grams of CO₂ contains 6.023 X 10²³ molecules of CO₂, therefore 1 molecule of CO₂ contains (44/6.023 X 10²³ )= 7.307 X 10^-23 grams of CO₂. We can also infer that 1 gram of CO₂  contains (6.023 X 10²³ /44) = 1.36 X 10²² molecules of CO₂.

This can be understood as:

We can also apply the mole concept to the composition of chemical compounds. Take an example of H_2. In this case, we use the mole as a common unit that we can apply as follows:

2 mol of H +1 mol of O =1 mol of  H₂O. In this chemical reaction, the moles of H and O describe the number of atoms of each element that react to form 1 mol of H₂O.

Avagadro’s Number

The number of particles present in one mole of any substance is 6.022 X 10²³. This value is the Avogadro number. So  1 mole = 6.022 X 10²³ particles in number. So, the mass of one mole of a molecule or ion is equivalent to its relative atomic or molecular mass in grams.

Avagadro number is named after the Amadeo Avagadros, the 19th-century Italian scientist and we can denote it by N₀. Mole is the Latin word for mass.

Formulae:  The following formulae can be helpful

1. of moles in a given amount of substance = (Atomic mass of substance/Molar mass of the substance)
2. of moles in a given amount of substance = (No. of particles of a substance/Avagadro’s number)