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Chemistry

Chemistry. Chapter 11 Empirical and Molecular Formulas. Empirical Formulas. The simplest whole number ratio of the elements in a compound (not necessarily the actual formula for a compound) Ex H 2 O 2 = HO H 2 O= H 2 O C 6 H 12 = CH 2 C 8 H 16 = CH 2

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Chemistry

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  1. Chemistry Chapter 11 Empirical and Molecular Formulas

  2. Empirical Formulas • The simplest whole number ratio of the elements in a compound (not necessarily the actual formula for a compound) • Ex • H2O2 = HO • H2O= H2O • C6H12 = CH2 • C8H16 = CH2 • Can be calculated from % composition

  3. Empirical Formula (Cheat Sheet) 1. % composition (if = 100%) converts to mass • Convert from mass to moles • Calculate simplest ratio (divide all # mol by the smallest # moles) 3 ½. If not all whole numbers, multiply all by a whole # to create whole #’s 4. Use simplest ratio as subscripts

  4. Examples • 11.2 % Hydrogen and 88.8% Oxygen

  5. Examples • 36.84% N and 63.16% O

  6. Examples • 60% C, 4.44%H, and 35.56% Oxygen

  7. Molecular Formula • Actual number of moles of each element in a compound • Need more info than just % comp • Need molar mass of the empirical formula • Need an experimental mass of the actual compound

  8. Molecular Formula (Cheat Sheet) • Use steps to calculate empirical formula • Calculate molar mass of empirical formula • The question will give you experimental mass of the compound • Experimental mass . Empirical form. Molar mass = 5. Multiply subscripts in empirical by your answer (whole number)

  9. Example • A colorless liquid is found to be composed of 46.68% N and 53.32% O and has a molar mass of 60.01 g/mol. What is the molecular formula?

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