 # EMPIRICAL AND MOLECULAR FORMULA EMPIRICAL FORMULAS An empirical

• Slides: 16 EMPIRICAL AND MOLECULAR FORMULA EMPIRICAL FORMULAS An empirical formula indicates the simplest whole-number ratio for a molecule CALCULATING EMPIRICAL FORMULAS Step 1: Convert grams to moles Step 2: Divide all numbers by the smallest value Step 3: Use whole number ratio as subscripts **You just need the mass of each element** EMPIRICAL FORMULA EXAMPLE What is the empirical formula for 2. 50 g of a compound containing 0. 900 g of Calcium and 1. 60 g of Chlorine? Determine the empirical formula of a compound containing 2. 644 g of gold and 0. 476 g of chlorine. DETERMINING EMPIRICAL FORMULA FROM % COMPOSITION Step 1: Assume 100 g, change % to grams Step 2: Convert moles to grams Step 3: Divide all numbers by the smallest Step 4: Use the # of moles as subscripts EMPIRICAL FORMULA EXAMPLE Find the empirical formula of a substance composed of 40. 00% C, 6. 67% H and 53. 33% O. WHAT IS THE EMPIRICAL FORMULA OF A COMPOUND THAT IS 25. 9% NITROGEN AND 74. 1% OXYGEN? MOLECULAR FORMULAS A molecular formula tells exactly how many atoms of each element are in a molecule. �It is a whole number multiple of the empirical formula. EMPIRICAL/MOLECULAR FORMULA Empirical Formula Molecular Formula An empirical formula indicates the simplest whole-number ratio for a molecule A molecular formula tells exactly how many atoms of each element are in a molecule. **Not common** Is a multiple of the empirical formula CH 2 C 2 H 4 C 5 H 10 Using ratios- think whole numbers DETERMINING MOLECULAR FORMULA FROM EMPIRICAL FORMULA Step 1: Divide the molar mass of the compound (given in the problem) by the molar mass of the empirical formula Step 2: Multiply each subscript by the answer to Step 2 **You need the actual molar mass of the compound** MOLECULAR FORMULA EXAMPLE Find the molecular formula of a compound with empirical formula of CH 2 O and molar mass of 180. 18 g . FINDING THE MOLECULAR FORMULA FROM THE PERCENT COMPOSITION Step 1: Find empirical formula Step 2: Divide the molar mass of the compound (given in the problem) by the molar mass of the empirical formula Step 3: Multiply each subscript by the answer to Step 2 MOLECULAR FORMULA EXAMPLE What is the formula of a gas whose molar mass is 30. 0 grams and whose composition is 20. 0 % H and 80. 0% C? A compound has an empirical formula of CH and a molar mass of 78 g/mol. What is its molecular formula. A brown gas has the empirical formula of NO 2. Its experimental molar mass is 46 g/mol. What is its molecular formula?