Empirical Formulas Unit 6 - Bonding

Review… Percent composition: –The relative amount of each element in a compound by mass. % composition Strategy: 1.Calculate GFM = Mass of Compound 2.Determine the mass of each element 3.Calculate % comp for each element

Review… Example: Find the % composition for the compound Mg(OH) 2

Empirical Formula Empirical formula – lowest whole # ratio of atoms of elements in a compound Example: C 6 H 12 O 6  CH 2 O In lab we can determine % composition of new compounds and can then calculate the empirical formula.

Empirical Formula Steps to Solving for the E.F. 1.Assume 100 g of compound (make the %  g) 2. Convert g of each element to moles 3. Divide each # of moles by the lowest # of moles 4. Change to whole #’s may have to multiply by – if ends in Write the formula

Empirical Formula 26.8% F and 73.2% Pb 26.8 g F 73.2 g Pb 1 mol F 1 mol Pb g F g Pb = 1.41 mol =.353 mol /.353 = 3.99 = 1.00  4  1 PbF 4

Empirical Formula 70.0% Mn and 30.0% O 70.0 g Mn 30.0 g O 1 mol Mn 1 mol O g Mn g O = 1.27 mol = 1.88 mol / 1.27 = 1.00 = 1.48 * 2 = 2 * 2 = 3 Mn 2 O 3

Empirical Formula 39.7% K, 27.9% Mn, and 32.4% O 39.7 g K 27.9 g Mn 1 mol K 1 mol Mn g K g Mn = 1.02 mol =.508 mol /.508 = 2.01 = 1.00  2  1 K 2 MnO g O1 mol O g O = 2.03 mol/.508 =  4