Mole - the Unit

A Mole is a unit of measurement. It describes amounts of a chemical substance, as defined by the number of elements the amount contains.

(Where an element is an atom of an element, a molecule of a substance, a charged a particle of an ion).

Moles measure quantities based on the number of atoms in a 12gm amount of carbon-12 - also known as Avogadro's Constant], or 6.02214179(30)×1023.

Atomic Mass

The atomic mass of an element is the mass of 1 mol of that element. E.g. Oxygen's 16.01 means that Oxygen has 16.01 grams per mol.

This can be calculated out for compounds by summing the atomic masses in the correct ratio.
E.g. H2O = 2(1.008) + 16 = 18.016

Molar Mass (M)

Molar Mass is the mass of 1 mole of a substance, and is calculated with:

  • Molar Mass = mass/moles
  • $M = \frac{m}{n}$

Concentration of an ion in a Solution

The concentration of an ion in a solution is the number of moles in 1L of that solution, multiplied by the ratio of that element.


  • K3PO4
  • Concentration of K+ = 3M
  • Concentration of PO43- = M

Calculating Moles in Various States