Presentation on theme: "EMPIRICAL FORMULA The empirical formula represents the smallest ratio of atoms present in a compound. The molecular formula gives the total number of atoms."— Presentation transcript:
1 EMPIRICAL FORMULAThe empirical formula represents the smallest ratio of atoms present in a compound.The molecular formula gives the total number of atoms of each element present in one molecule of a compound.The empirical formula is the simplest formula and the molecular formula is the “true” formula.
2 EMPIRICAL FORMULA Mass % of Empirical elements Formula Grams of Assume g sample Calculate mole ratioUse Atomic MassesMass % ofelementsEmpiricalFormulaGrams ofeachelementMoles ofeachelement
3 EMPIRICAL FORMULAStep 1: If given the % composition, assume a 100g sample then convert % to grams.Step 2: Use the atomic masses to convert grams to moles.Step 3: Divide the moles of each element by the SMALLEST mole fraction.Step 4: The results from step 3 should be a whole number, if not, make it so by multiplying by a common factor.
4 Empirical Formula = Na2CO3 1. Calculate the empirical formula from a sample containing 43.4% Na, 11.3% C, and 45.3% O.smallest43.4% 43.4 g Na (1 mole / 23 g/mol) =1.887 moles Na11.3% 11.3 g C (1 mole / 12 g/mol) = moles C45.3% 45.3 g O (1 mole / 16 g/mol) = moles O1.887/ =2.00 Na2.831/ = 3.00 O .9417/.9417 = 1.00 CEmpirical Formula = Na2CO3
5 Empirical Formula = CaO 2. When 8.00 g of calcium metal is heated in air, g of metal oxide is formed. Calculate the empirical formula.According to the Law of Conservation of mass,11.20 g Product g Ca = 3.20 g Oxygen (reactive part of air)smallest8.00 g Ca (1 mole / 40 g/mol) = moles Ca3.20 g O (1 mole / 16 g/mol) = moles O0.200 / = 1Empirical Formula = CaO
6 Empirical Formula = SrCl2 . 6 H2O 3. A compound was found to have a composition of 33.0 % Sr, 26.8 % Cl, and 40.2 % water. Calculate the empirical formula of this hydrate.smallest33.0% 33.0 g Sr (1 mole/87.6 g/mol) = moles Sr26.8% 26.8 g Cl (1 mole/35.45 g/mol) = moles Cl40.2% 40.2 g H2O (1 mole/18.0g/mol) = moles H2O/ = 2 Cl / = 5.9 = 6 H2OEmpirical Formula = SrCl2 . 6 H2O
7 EMPIRICAL FORMULA & Molecular Formula 4. Propylene contains 14.3 % H, 85.7% C, and has a molar mass of 42.0 g/mol. What is its molecular formula? smallest14.3% 14.3 g H (1 mole/1.01 g/mol) = moles H85.7% 85.7 g C (1 mole/12.01 g/mol) = moles C14.19 / = = 2 HEmpirical Formula = CH2Molar mass / empirical mass = multipier(42.0 g/mol / 14.0 g/mol) = 33 x CH2 becomes the molecular formula C3H6
8 PRACTICE PROBLEM #12 A K2MnO4 Bi2O3 C6H12O3 ______ Which contains the larger number of MOLES of atoms?a) g KCl b) 25.0 g CaSO c) g of N2______ What is the empirical formula of the compound whose composition is 39.7% K, 27.8% Mn, and 32.5% O?______ Determine the empirical formula of a compound that contains 89.7 % bismuth and 10.3 % oxygen.______ Write the molecular formula for a compound that contains 54.5 % C, 9.1% H, and 36.4 % O and has a molar mass of 132 amu?K2MnO4Bi2O3C6H12O3
9 GROUP STUDY PROBLEM #12______ Which contains the larger number of MOLES of atoms?a) g HBr b) 25.0 g C6H11O6 c) g of Br2______ A sample of a compound weighing 4.18 g contains 1.67 g of sulfur and the rest is oxygen. What is the empirical formula?______ 3. What is the empirical formula of the compound whose composition is 28.7% K, 1.4% H, 22.8 % P, and 47.1% O?______ A compound contains 92.3% C and 7.7% H and has a molar mass of 78.0 g/mol. Determine the molecular formula.