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Exploring Empirical and Molecular Formulas in AP Chemistry

Learn the concepts of empirical and molecular formulas in chemistry, understand their significance, and solve practice problems to strengthen your understanding.

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Exploring Empirical and Molecular Formulas in AP Chemistry

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  1. Chapter 2 Part 2 AP Chemistry 2012

  2. Empirical And Molecular Formulas • What do the following molecular formulas have in common? C6H12, C3H6, C2H4, CH2 • Each of the above molecules have a carbon to hydrogen ratio of 1 to 2. (Or they contain twice as many hydrogen atoms as carbon atoms)

  3. Empirical Formulas • An empirical formula contains the lowest whole number ratio of atoms. • In the previous example, this would be CH2 • Other empirical formulas: H2O C4H8O NO3 CH4

  4. Molecular Formulas • Molecular formulas represent the actual molecule and are based on molar mass. • The molecular formula of the molecule below is C4H10, what is its empirical formula?

  5. Note • A molecular formula can also be an empirical formula.

  6. Determining Molecular Formulas • Question: What is the molecular formula of a compound with the empirical formula C2H6O and a molar mass of 138 g/mol? Solution: 1. Find the molar mass of the empirical formula 2. Divide the molar mass of m.f. by e.f. 3. Multiply the subscripts on the e.f. by the answer you obtained in #2 (2×12g/mol) + (6×1g/mol) + (1×16g/mol) = 46 g/mol 138 g/mol ÷ 46 g/mol = 3 C2 × 3H6 × 3O1 × 3

  7. Book Practice Problems page 71: 2.8, 2.44, 2.50, 2.54, 2.56, 2.66

  8. How does a calcium ion form from a calcium atom?  How many protons, neutrons, and electrons do a calcium atom and ion have?  How does the formation of a cation from a neutral atom differ from the formation of an anion from a neutral atom? • Why don’t we write the formula of the ionic compound formed between Ba2+ and S2- as Ba2S2?  Why is CrO named chromium (II) oxide while CaO is calcium oxide?

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