Use of amount of substance in relation to masses of pure substances

3.2.1 Moles (HT only)

Moles

Avogadro constant = 6.02 × 10²³

No of molecules = mole × 6.02 × 10²³

Mass of 1 mol of a substance

= relative atomic mass (Ar) in grams if substance is an element

= relative formula mass (Mr) in grams if substance is a compound

Reacting masses

Eg If I react 10g of CaCO₃ with excess HCl, what mass of CaCl₂ should I produce?

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

3.2.2 Amounts of substances in equations (HT only)

(Linked to other sub-topics)

3.2.3 Using moles to balance equations (HT only)

(Linked to other sub-topics)

3.2.4 Limiting reactants (HT only)

Mr of TiCl4 = 190

Na is in excess as n(Na) = 870 mol is more than 844 mol needed or n(TiCl₄) = 211 mol is less than 217.5 mol needed

3.2.5 Concentration of solutions

(See 3.4 Using concentrations of solutions in mol/dm3 (chemistry only) (HT only))