What is a Mole? Learn Formula and Easy Ways to Calculate Moles

The mole is one of the most important concepts in chemistry, but it can seem confusing at first. In simple words, a mole helps us count very tiny particles like atoms and molecules easily. Just like we use a dozen to count 12 items, chemists use the mole to count particles. In this post, you will learn what a mole is and explore simple methods to calculate moles using easy formulas and examples.

What is a Mole?

A mole is the amount of substance that contains as many species (atoms, molecules, ions and other species) as there are atoms in exactly 12g of C-12.

Mass of one atom of C-12 = 1.99×10^-23g

No of atoms in 12g of C-12 = 12/1.99×10^-23g
= 6.022×10²³ g (Avagadron’s Number N_A)

One mole is the collection of 6.022×10²³ g particles. (atoms, molecules, ions, etc.)
1 mol of Na = 6.022×10²³ g atoms of Na
1 mol of H₂ gas = 6.022×10²³ g molcules of H₂
1 mol of NaCl = 6.022×10²³ g formula unit of NaCl
1 mol of Cl^– = 6.022×10²³ g ions of Cl^–

Molar Mass

It is the mass of one mole of substance.

For atoms: Molar Mass = Gram Atomic Mass
For Molecules: Molar Mass = Gram Molecular Mass

Molar Mass of He = 4g/mol
Molar Mass of Oxygen = 16g/mol

Methods to Calculate Moles

In Terms of Mass:

For example:

Convert 36g of Carbon into moles?

In Terms of the number of Particles:

For example:

Convert 6.022×10²¹ atom of H into moles?\

In terms of Volume of Gas:

At STP(Standard Temperature and Pressure):

Old STP = T = 0^o C = 273.15K
P = 1 atm
New STP = T = 0^o C = 273.15K
P = 1 bar

1 atm = 1.012 bar
1 bar = 0.987 atm

From the ideal gas equation, PV = NRT
0.987 x V = 1 x 0.087 x 273.15K
V = 22.7L
Old STP, PV = NRT
1 x V = 1 x 0.087 x 273.15K
V = 22.4L

Y-Map to Calculate the Moles