Pluchino – Regents Chemistry The Mole & Stoichiometry – 04 Empirical & Molecular Formulas Aim: How can we determine the empirical and molecular formula of a compound? Do Now: The ratio of C to H atoms in a compound is 1:2. The molar mass is 42 g/mol. What is the formula of the compound? Empirical Formula: shows the ratio of atoms in a compound in the lowest terms Molecular Formula: shows the number and type of each atom in a compound A compound is 20% H and 80% carbon by mass. What is its empirical formula? Finding the Empirical Formula 1. Assume 100 g of the sample. 2. Divide the mass of the element in the compound by its molar mass to get the number of moles of each element. 3. Divide everything by the smallest number of moles. 4. The resulting numbers become the subscript for each element. The molar mass of the compound with the empirical formula of CH
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