# Percent Composition Empirical Formulas and Molecular Formulas Percent

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Percent Composition, Empirical Formulas, and Molecular Formulas

Percent Composition • percent composition: the percentage by mass of each element in a compound Part _______ Percent = Whole x 100% mass of element in compound _____________ x 100% % element = mass of compound

Percent Composition Example mass of element in compound _____________ x 100% % element = mass of compound What is the percent composition of the element carbon in CH 3 COOH?

Percent Composition Example mass of element in compound _____________ x 100% % element = mass of compound What is the percent composition of each element in calcium chloride?

Empirical Formulas Molecular Formula: chemical formulas that indicate the actual numbers and types of atoms in a molecule Empirical Formula: chemical formulas that give only the relative number of atoms • the “simplified/reduced form” of the formula *Often the same!

Empirical Formula Example Remember: A chemical formula tells us the number of MOLES of each element – you MUST convert grams to moles!!! Example: A compound contains 63. 57 g Fe and 36. 43 g O. What is its empirical formula?

Empirical Formula Example Remember: A chemical formula tells us the number of MOLES of each element – you MUST convert grams to moles!!! Example: What is the empirical formula for a compound with 18. 8% nickel and 81. 2% iodine?

Hydrates Hydrate: a chemical compound that contains water as part of its structure

Hydrate Example You perform an experiment to determine the molecular formula of a nickel sulfate hydrate, Ni. SO 4 • x. H 2 O. The mass of the hydrate before heating is 3. 00 g. The mass of the anhydrous compound after heating is 1. 76 g. What is the molecular formula of the hydrate?