Empirical Formulas Compare the following compounds: HgO vs. Hg 2 O 2 C 2 H 6 vs. C 4 H 12 Empirical Formulas: Lowest-ratio formulas What do the subscripts mean??? C 2 H 6 2 atoms of C, 6 atoms of H 2 moles of C, 6 moles of H

Can be Determined from % Composition! 1. Change % to grams 2. Change grams to moles 3. Divide by smallest # of moles to get ratio 4.Write Formula Example: Find the E.F. for a compound with the % composition given % Na, 22.58% S and 45.05% O % C, 5.08% H, and 54.24% O Empirical Formulas

Molecular Formulas aka TRUE formulas Consider the following compounds: C 2 H 6 vs. C 4 H 12 Both multiples of CH 3 Mol Forms are a multiple of the Emp Form Need 2 things: –The Empirical Formula –The Multiplier

Steps 1. Determine the Empirical Formula (EF) 2. Find the Molar Mass (MM) of the EF 3. Must be given the actual MM; Divide Actual MM by EF MM to get multiplier 4.Write Formula! Example A compound has an E.F. of CH 2 and a Molar Mass of 56 g/mol. What is the M.F.? Molecular Formulas aka TRUE formulas