Empirical formula: simplest ratio of the atoms of different elements in a compound
Molecular formula: the actual number of each kind of atom in a molecule of a substance
Ethane, for example, has an empirical formula of CH3 and a molecular formula of C2H6. There are 2 ‘units’ of CH3 in C2H6.
Practice questions
1. Determine the empirical formula of a compound containing 40.0% carbon, 6.6% hydrogen and 53.4% oxygen.
[Tip: assume you have 100g of the compound, in which case 40% = 40g)
2. A mineral was analysed and it was found to contain 12.1% Na, 14.2% Al, 22.1% Si, 42.1% O and 9.48% H2O. What is the formula?
3. A 10.00g sample of a compound contains 3.91g of carbon, 0.87g of hydrogen and the remainder is oxygen. Determine the empirical formula.
Answers
1. CH2O
2. Na2Al2Si3O10 ï2H2O
3. C3H8O3