1.27 know that the mole (mol) is the unit for the amount of a substance

A mole is that amount of substance that contains 6.02 x 1023 atoms, molecules etc.
This number is known as the Avogadro constant

Molar masses

• A mole of an element will have a mass equal to its Ar but in grams
• A mole of a compound will have a mass equal to its Mr but in grams

Moles tell you how many particles are present, and the ratio of moles tells you the ratio of particles that are represented by an equation. 

You can find out how many moles are present by dividing the mass by the Mr:

number of moles = mass ÷ Mr