Empirical and Molecular Formulas 2011

Empirical and Molecular Formulas An empirical formula shows the simplest whole number ratio of atoms of each element in a compound A molecular formula shows the actual number of atoms of each element in a compound

Example: Glucose Glucose has a molecular formula of: – C 6 H 12 O 6 It has an empirical formula of: – CH 2 O

Formulas cont’d A molecular formula is always a multiple of empirical formula A compound has ONE molecular formula Many compounds have the same empirical formula

Example An compound contains 28.4g of copper and 71.6g of bromine. Calculate the empirical formula of the compound: 1.Convert all grams to moles 2.Divide all numbers of moles by the smallest # present (do a ratio!) 3.Multiply all numbers by the smallest # that will make them WHOLE NUMBERS

Example What is the empirical formula for a compound that contains: 77.3% Silver, 7.4% phosphorous and 15.3% O? Convert all grams to moles Divide all numbers of moles by the smallest # present (do a ratio!) Multiply all numbers by the smallest # that will make them WHOLE NUMBERS

Example What is the empirical formula for a compound that contains 5.51 g of cobalt and 4.49 g of sulfur? Convert all grams to moles Divide all numbers of moles by the smallest # present (do a ratio!) Multiply all numbers by the smallest # that will make them WHOLE NUMBERS

Molecular formulas from empirical formulas A white powder is analyzed and found to have an empirical formula of P 2 O 5. It has a molar mass of g/mol. What is the molecular formula for this compound?