percent composition and chemical formulas
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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.
10.3
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Percent Composition and Chemical Formulas
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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?
10.3
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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%.
10.3
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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.
10.3
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SAMPLE PROBLEM
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10.9
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SAMPLE PROBLEM
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10.9
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SAMPLE PROBLEM
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10.9
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Practice Problems for Sample Problem 10.9
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Percent Composition and Chemical Formulas
> The Percent Composition of a Compound
Percent Composition from the Chemical Formula
10.3
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SAMPLE PROBLEM
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10.10
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SAMPLE PROBLEM
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10.10
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SAMPLE PROBLEM
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10.10
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Practice Problems for Sample Problem 10.10
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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.
10.3
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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.
10.3
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Percent Composition and Chemical Formulas
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Empirical Formulas
Empirical Formulas
What does the empirical formula of a compound show?
10.3
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Percent Composition and Chemical Formulas
> Empirical Formulas
The empirical formula gives the lowest whole-number 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.
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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.
10.3
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SAMPLE PROBLEM
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10.11
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SAMPLE PROBLEM
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10.11
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SAMPLE PROBLEM
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10.11
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SAMPLE PROBLEM
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10.11
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Practice Problems for Sample Problem 10.11
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Percent Composition and Chemical Formulas
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Molecular Formulas
Molecular Formulas
How does the molecular formula of a compound compare with the empirical formula?
10.3
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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.
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Percent Composition and Chemical Formulas
> Molecular Formulas10.3
Methanal, ethanoic acid, and glucose all have the same empirical formula—CH2O.
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Percent Composition and Chemical Formulas
> Molecular Formulas10.3
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SAMPLE PROBLEM
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10.12
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SAMPLE PROBLEM
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10.12
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SAMPLE PROBLEM
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10.12
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SAMPLE PROBLEM
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10.12
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Practice Problems for Sample Problem 10.12
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Section Quiz
-or-Continue to: Launch:
Assess students’ understanding of the concepts in Section
10.3 Section Quiz.
10.3.
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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
10.3 Section Quiz.
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2. Which of the following is NOT an empirical formula?
a. NO2
b. H2N
c. CH
d. C3H6
10.3 Section Quiz.
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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
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