define and use empirical and molecular formulae

Empirical and molecular formulas are both used in chemistry to denote the composition of compounds.

1. Empirical Formula: This is the simplest, most reduced ratio of elements in a compound. It does not provide the actual number of atoms in a molecule, but it does provide the simplest whole number ratio of atoms. For example, the empirical formula of glucose is CH2O, which means for every carbon atom, there are two hydrogen atoms and one oxygen atom.

2. Molecular Formula: This is the actual number of atoms of each element in a molecule of the compound. It can be the same as the empirical formula, or it can be a multiple of the empirical formula. For example, the molecular formula of glucose is C6H12O6, which means there are 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.

To use these formulas, you would first determine the empirical formula from the percent composition of a compound. Then, if the molar mass of the compound is known, you can find the molecular formula. For example, if you know a compound is 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass, and has a molar mass of about 180 g/mol, you can find the empirical formula is CH2O, and the molecular formula is C6H12O6.