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Percent Composition and Chemical Formulas Prentice-Hall Chapter 10.3 Dr. Yager
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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.
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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%.
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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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Percent Composition from the Chemical Formula
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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.
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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.
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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.
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Empirical Formulas The empirical formula of a compound shows the smallest whole-number ratio of the atoms in a compound.
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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
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Methonal, ethanoic acid, and glucose all have the same empirical formula - CH 2 O.
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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
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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
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2. Which of the following is NOT an empirical formula? a)NO 2 b)H 2 N c)CH d)C 3 H 6
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2. Which of the following is NOT an empirical formula? a)NO 2 b)H 2 N c)CH d)C 3 H 6
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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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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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