Unit 6.6-6.7 Empirical and Molecular Formulas. Empirical Formulas Consists of the symbols for the elements combined in a compound, with subscripts showing.

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Presentation transcript:

Unit Empirical and Molecular Formulas

Empirical Formulas Consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole- number ratio of the different atoms in the compound. Huh?!? In other words, its a chemical formula in the simplest ratio. C 2 H 6 → CH 3

Empirical Formula from Percent Composition 1) Convert the percent to grams. 2) Convert grams to moles by dividing by the molar mass of each element. 3) Divide each amount by the smallest molar value to determine ratios. 4) Multiply each molar ratio until all elements are whole numbers. Example: What is the empirical formula for a compound that is 38.77% Cl and 61.23% O by mass?

Empirical Formula Practice Problem A hydrate is analyzed and has a percent composition of 13.5% Ca, 10.8 % O, and 0.675% H. The rest of the compound is made of water and is not considered relevant. What is the empirical formula of this compound?

Molecular Formula Whole number multiple of the empirical formula. Gives the exact number of atoms in the molecule not just the simplest ratio. Example: A compound has an empirical formula of CH 2 O, but has a mass of 90.0 g/mol. What is the correct molecular formula?

Molecular Formula Practice Problem Hydrogen peroxide is a common household disinfectant. When analyzed, it has a composition of 5.88% H and 94.12% O. It has a molar mass of 34 g/mol. What is the molecular formula for hydrogen peroxide?