The mass of one mole of a substance is equal to:

• the relative atomic mass (Ar) of its formula in grams if the substance is an element

• the relative formula mass (Mr) of its formula in grams if the substance is a compound

You can use moles to calculate masses in reactions

• Remember those balanced equations, well the big numbers in front of the chemical formulas of the reactants and products tell you how many moles of each substance takes part or is formed during the reaction

You can balance equations using reacting masses

• If you know the masses of the reactants and products that took part in a reaction, you can work out the balanced symbol equation for the reaction

  • Divide them mass of each substance by its relative formula mass to find the number of moles

  • Divide the number of moles of each substance by the smallest number of moles in the reaction

  • If any of the numbers aren’t whole numbers, multiply all the numbers by the same amount so that they all become whole numbers

  • Write the balanced symbol equation for the reaction by putting these numbers in front of the chemical formulas