Empirical Formula

• the most reduced ratio of atoms of atoms in a compound (all ionic compounds ar empirical formulas)

EX: CH2O, HO, NaCl, H2O, MgSO4

To calculate:

• convert % to mass
• convert mass to moles
• find whole number ratio of moles by dividing by smallest amount of moles
• use ratios as subscripts on formula

EX: What is the empirical formula for a compound that is 30%C, 30% H, 40%O?

Use a 100g sample...

    30g C X 1mole/12 g C = 2.5 moles of C/2.5 = 1

    30g H X 1 mole/1 g H = 30 moles of H/2.5 = 12

    40g O X 1 mole/16 g O = 2.5 moles of O/2.5 = 1

    CH12O

Molecular Formula

• the actual ratio of atoms in a compound (would be a multiple of empirical formula

EX: C6H12O6, H2O2

To calculate:

• determine mass of empirical formula
• divide your molecular mass by your empirical mass
• multiply subscripts in empirical formula by your answer

EX:   What is the molecular formula for a compound that has an empirical formula of CH12O and a molecular mass of 80g/mol?

CH12O--> 12+12+16 = 40 g/mol

80g/mol / 40g/mol = 2

C2H24O2