Transcript Notes #2
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 – H2O2 = HO – H2O= H2O – C6H12 = CH2 – C8H16 = CH2 • Can be calculated from % composition Empirical Formula (Cheat Sheet) 1. % composition (if = 100%) converts to mass 2. Convert from mass to moles 3. 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 Examples • 11.2 % Hydrogen and 88.8% Oxygen Examples • 36.84% N and 63.16% O Examples • 60% C, 4.44%H, and 35.56% Oxygen 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 Molecular Formula (Cheat Sheet) 1. Use steps to calculate empirical formula 2. Calculate molar mass of empirical formula 3. The question will give you experimental mass of the compound 4. Experimental mass . = Empirical form. Molar mass 5. Multiply subscripts in empirical by your answer (whole number) 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?