Empirical and Molecular Formulas What formulas???? Empirical Formula Simplest/general formula for chemical compound Many compounds can have the SAME empirical formula Lowest whole number ratio of atoms in a compound Sometimes actual chemical formula Ionic compounds, some molecular compounds Molecular Formulas “true” formula Represents the true number of atoms of each element in a chemical compound Multiple of empirical formula Molecular Formula = (empirical formula)n C6H6 = Calculating the Empirical Formula 1) Assume 100g sample of chemical compound. Find the moles of each element in 100g of compound. 1) Divide each mole value by the SMALLEST value! 1) Multiply each number by integer to get ALL whole numbers. Example 1: Vitamin C is made up of 40.9% C, 54.5% O, and 4.58% H. What is the empirical formula? If Vitamin C has a molecular mass of 176g. What is the molecular formula? Example 2: Adipic acid contains 49.32%C, 43.84%O, and 6.85%H by mass. What is the empirical formula for adipic acid? How do we calculate the molecular formula? MUST know two pieces of information Empirical Formula or Percent Composition of a compound. AND Molecular Mass (formula mass for the entire compound) **Divide the molecular mass by the empirical formula mass. MM/EM = multiple (empirical formula)multiple = molecular formula Example 3: Trichloroisocyanuric acid, found in household bleaches, has an empirical formula of OCNCl. The molar mass of the compound is 232.41g. What is the compound’s molecular formula? Example 4: A chemical compound is found to have an empirical formula of NH2. The molecular mass is 32.06g. What is the molecular formula for this compound? Practice, Practice !!!