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Percent Composition and Chemical Formulas Prentice-Hall Chapter 10.3 Dr. Yager.

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Presentation on theme: "Percent Composition and Chemical Formulas Prentice-Hall Chapter 10.3 Dr. Yager."— Presentation transcript:

1 Percent Composition and Chemical Formulas Prentice-Hall Chapter 10.3 Dr. Yager

2 Objectives  Describe how to calculate the percent of mass of an element in a compound.  Interpret an empirical formula.  Distinguish between empirical and molecular formulas.

3 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%.

4 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.

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7 Percent Composition from the Chemical Formula

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10 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.

11 Propane (C 3 H 8 ) 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 C 3 H 8.

12 Ethyne (C 2 H 2 ) is a gas used in welder’s torches. Styrene (C 8 H 8 ) is used in making polystyrene. These two compounds of carbon have the same empirical formula (CH) but different molecular formulas.

13 Empirical Formulas The empirical formula of a compound shows the smallest whole-number ratio of the atoms in a compound.

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17 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. Molecular Formula Compared to Empirical Formula

18 Methonal, ethanoic acid, and glucose all have the same empirical formula - CH 2 O.

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22 1. Calculate the percent by mass of carbon in cadaverine, C 5 H 14 N 2, a compound present in rotting meat. 1. Calculate the percent by mass of carbon in cadaverine, C 5 H 14 N 2, a compound present in rotting meat. a)67.4% C b)58.8% C c)51.7% C d)68.2% C

23 1. Calculate the percent by mass of carbon in cadaverine, C 5 H 14 N 2, a compound present in rotting meat. 1. Calculate the percent by mass of carbon in cadaverine, C 5 H 14 N 2, a compound present in rotting meat. a)67.4% C b)58.8% C c)51.7% C d)68.2% C

24 2. Which of the following is NOT an empirical formula? a)NO 2 b)H 2 N c)CH d)C 3 H 6

25 2. Which of the following is NOT an empirical formula? a)NO 2 b)H 2 N c)CH d)C 3 H 6

26 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)C 2 H 4 O 2 b)CH 2 O c)C 2 H 3 O d)C 2 H 4 O

27 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)C 2 H 4 O 2 b)CH 2 O c)C 2 H 3 O d)C 2 H 4 O


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