Empirical and Molecular Formulas

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Empirical and Molecular Formulas
Unit

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:
C6H12O6 It has an empirical formula of: CH2O

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 0.18 grams of magnesium react with 0.12 grams of oxygen to form magnesium oxide 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 An oxide of aluminum is formed with g of Aluminum and g of Oxygen. Calculate the empirical formula of the compound: 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

Find molecular formulas from empirical formulas
A white powder is analyzed and found to have an empirical formula of P2O5. It has a molar mass of g/mol. What is the molecular formula for this compound?

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