10.3 Percent Composition and Chemical Formulas It helps to know the percents of the components in a shirt because they affect how warm it is, whether it will need to be ironed, and how it should be cleaned. You will learn how the percents of the elements in a compound are important in chemistry. Slide 1 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > The Percent Composition of a Compound The Percent Composition of a Compound How do you calculate the percent by mass of an element in a compound? Slide 2 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > The Percent Composition of a Compound The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%. Slide 3 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > The Percent Composition of a Compound Percent Composition from Mass Data The relative amounts of the elements in a compound are expressed as the percent composition or the percent by mass of each element in the compound. Slide 4 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.9 Slide 5 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.9 Slide 6 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.9 Slide 7 of 40 © Copyright Pearson Prentice Hall End Show Practice Problems for Sample Problem 10.9 Slide 8 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > The Percent Composition of a Compound Percent Composition from the Chemical Formula Slide 9 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.10 Slide 10 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.10 Slide 11 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.10 Slide 12 of 40 © Copyright Pearson Prentice Hall End Show Practice Problems for Sample Problem 10.10 Slide 13 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > The Percent Composition of a Compound Percent Composition as a Conversion Factor You can use percent composition to calculate the number of grams of any element in a specific mass of a compound. Slide 14 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > The Percent Composition of a Compound Propane (C3H8) is 81.8% carbon and 18% hydrogen. You can calculate the mass of carbon and the mass of hydrogen in an 82.0 g sample of C3H8. Slide 15 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > Empirical Formulas Empirical Formulas What does the empirical formula of a compound show? Slide 16 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > Empirical Formulas The empirical formula gives the lowest wholenumber ratio of the atoms of the elements in a compound. The empirical formula of a compound shows the smallest whole-number ratio of the atoms in the compound. Slide 17 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > Empirical Formulas Ethyne (C2H2) is a gas used in welder’s torches. Styrene (C8H8) is used in making polystyrene. These two compounds of carbon have the same empirical formula (CH) but different molecular formulas. Slide 18 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.11 Slide 19 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.11 Slide 20 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.11 Slide 21 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.11 Slide 22 of 40 © Copyright Pearson Prentice Hall End Show Practice Problems for Sample Problem 10.11 Slide 23 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > Molecular Formulas Molecular Formulas How does the molecular formula of a compound compare with the empirical formula? Slide 24 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > Molecular Formulas The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple whole-number multiple of its empirical formula. Slide 25 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > Molecular Formulas Methanal, ethanoic acid, and glucose all have the same empirical formula— CH2O. Slide 26 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Percent Composition and Chemical Formulas > Molecular Formulas Slide 27 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.12 Slide 28 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.12 Slide 29 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.12 Slide 30 of 40 © Copyright Pearson Prentice Hall End Show SAMPLE PROBLEM 10.12 Slide 31 of 40 © Copyright Pearson Prentice Hall End Show Practice Problems for Sample Problem 10.12 Slide 32 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Section Quiz. Assess students’ understanding of the concepts in Section 10.3. Continue to: -or- Launch: Section Quiz Slide 33 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Section Quiz. 1. Calculate the percent by mass of carbon in cadaverine, C5H14N2, a compound present in rotting meat. a. 67.4% C b. 58.8% C c. 51.7% C d. 68.2% C Slide 34 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Section Quiz. 2. Which of the following is NOT an empirical formula? a. NO2 b. H2N c. CH d. C3H6 Slide 35 of 40 © Copyright Pearson Prentice Hall End Show 10.3 Section Quiz. 3. Determine the molecular formula of a compound that contains 40.0 percent C, 6.71 percent H, and 53.29 percent O and has a molar mass of 60.05 g. a. C2H4O2 b. CH2O c. C2H3O d. C2H4O Slide 36 of 40 © Copyright Pearson Prentice Hall End Show
