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Wake-up 1. Determine the empirical formula for the following: 28.4% Copper and 71.6% Bromine Molecular Formula What are Molecular Formulas? How to calculate molecular formulas? Empirical Formula A chemical formula that shows the lowest whole number ratio of all atoms in a compound Molecular Formula A chemical formula that shows the total number and kinds of atoms in a molecule Recall from yesterday Compound A is Empirical Formula Compound B is Molecular Formula How to find Molecular Formulas? 1. Write down what you know. The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of butane? Empirical formula = C2H5 Molar Mass = 60g/mol How to find Molecular Formulas? 2. Calculate/Find the Empirical Formula (if needed) The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of butane? C2H5 How to find Molecular Formulas? 3. Calculate the empirical formula mass (efm) using the empirical formula C = 2 x 12.01 = 24.02 H = 5 x 1.00 = 5 Empirical Formula Mass = 24.02 + 5 29.02 How to find Molecular Formulas? 4. Divide the molar mass (that is provided in the problem) by the empirical formula mass The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of butane? 60g/mol 29.02g = 2 mole How to find Molecular Formulas? 5. Multiply the empirical formula subscripts by the whole number you found in step 4 to get the molecular formula. C2H5 x 2 = C4H10 Example #1 The simplest formula for vitamin C is C3H4O3. Experimental data indicates that the molecular mass of vitamin C is about 180 g/mol. What is the molecular formula of vitamin C? Example #2 A compound contains 18.8% sodium, 29% chlorine, and 52.2% oxygen, by mass. If the molar mass of the compound in 122.44 g/mol, determine the empirical and molecular formulas. Example #3 Caffeine has an elemental analysis of 49.48% carbon, 5.190% hydrogen, 16.47% oxygen, and 28.85% nitrogen. It has a molar mass of 194.19 g/mol. What is the molecular formula of caffeine? Molecular Formula What are Molecular Formulas? How to calculate molecular formulas?