Empirical Formulas.

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Presentation transcript:

Empirical Formulas

Empirical formula – lowest whole-number ratio of the elements in a compound (divide by – Greatest Common Factor) What is the empirical formula of C2N2H8 CNH4

Empirical Formula Calculations 1.) Change the given information to moles for each element. 2.) Divide each mole answer by the smallest number of moles. 3.) If the answers from step 2 are not whole numbers then divide by the smallest decimal part. 4.) Write the formula with the mole ratio as subscripts.

EX 1 Find the empirical formula. A compound contains 9.31g of Ag and 0.69g of O.

Ag2O

EX 2 A compound contains 25.9% N and 74.1% O. Find the empirical formula.

Nitrogen = 1 ÷ 0.5 = 2 Oxygen = 2.5 ÷ 0.5 = 5 N2O5

MOLECULAR FORMULAS

Molecular formula – empirical formula or its multiple Several compounds can have the same empirical formula but different molecular formulas. What is the empirical formula of C2N2H8? CNH4 What is the molecular formula of CNH4? C2N2H8

Convert molecular  empirical Divide subscripts by greatest common factor Convert empirical  molecular multiply subscripts by …

EX 1 The empirical formula is CH4N and the molar mass is 60.0 g. Find the molecular formula. C 1 X 12.0 = 12.0g 4H 4 X 1.0 = 4.0g N 1 X 14.0 = 14.0g 30.0g C2H8N2

EX 2 Find the molecular formula of C4H6O if the molar mass is 280.0g. 4C 1 X 12.0 = 48.0g 6H 4 X 1.0 = 6.0g O 1 X 14.0 = 16.0g 70.0g C16H24O4