1 / 23

Empirical and Molecular Formulas

Empirical and Molecular Formulas. Section 11.4 Chemistry. Objectives. Explain what is meant by the percent composition of a compound. Determine the empirical and molecular formulas for a compound from mass percent and actual mass data. Key Terms. Percent composition Empirical formula

kerry
Télécharger la présentation

Empirical and Molecular Formulas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Empirical and Molecular Formulas Section 11.4 Chemistry

  2. Objectives • Explain what is meant by the percent composition of a compound. • Determine the empirical and molecular formulas for a compound from mass percent and actual mass data.

  3. Key Terms • Percent composition • Empirical formula • Molecular formula

  4. Percent Composition • Percent by mass of each element in a compound. • Mass of Element x 100 Mass of Compound

  5. Example • Calculate percent composition of H in H2O • Molar mass of water: 18.02 g/mol • Determine mass of H in 1 mol of H2O

  6. Mass of H • 1.01 x 2 = 2.02 g H in 1 mol water Atomic mass of H from periodic table Number of H in H2O

  7. Percent Composition of H • 2.02 g of H x 100 = 11.2% H 18.02 g of H2O

  8. Empirical Formula • Formula for a compound with the smallest whole-number ratio of elements. • Percent composition can be used to find the chemical formula.

  9. Empirical Formula • When given percent composition, assume: • The total mass of the compound is 100 g • The percent composition of the element is equal to the mass in grams of the element.

  10. Example • A compound has a percent composition of 40.05% S and 59.95% O. • So in 100 g of the compound, 40.05 g are S and 59.95 g are O. • Find the amount of mol for each element.

  11. Empirical Formula • 40.05g S x 1 mol S = 1.249 mol S 32.07g S • 59.95g O x 1 mol O = 3.747 mol O 16.00g O

  12. Empirical Formula • The element with the smallest number of mol gets the subscript 1.

  13. Empirical Formula • S has a subscript 1 • Then divide the mol O by the mol S • 3.747 mol O/ 1.249 mol S = 3 mol O • Then write your empirical formula using your subscripts: SO3

  14. Practice Problems • Pg. 333

  15. Molecular Formula • Formula that specifies the actual number of atoms of each element in one molecule or formula unit of a substance. • n = molecular formula mass empirical formula mass

  16. Example • Compound is composed of 40.68% carbon, 5.08% hydrogen, and 54.24% oxygen and has a mass of 118.1 g/mol. Determine the empirical and molecular formulas for succinic acid.

  17. Example • 40.68 g C x 1 mol C = 3.387 mol C 12.01 g C • 5.08 g H x 1 mol H = 5.04 mol H 1.008 g H • 54.24 g O x 1 mol O = 3.390 mol O 16.00 g O

  18. Example • 3.387 mol C/ 3.387 = 1 mol C • 5.040 mol H/ 3.387 = 1.49 = 1.5 mol H • 3.390 mol O/ 3.387 = 1.001 = 1 mol O • Ratio of C : H : O = 1 : 1.5 : 1

  19. Example • Empirical Formula: C2H3O2

  20. Example • To find molecular formula, calculate n. • n = molecular formula mass empirical formula mass • Molecular mass is in the problem! • Calculate molar mass of empirical

  21. Example • n = 118.1 = 2 59.04 • Multiply the subscripts of the empirical by n to find the molecular formula. • Molecular Formula: C4H6O4

  22. Practice Problems • Pg 335

  23. Homework • Section 11.4 Problems 27-29 on page 877

More Related