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© Copyright Pearson Prentice Hall
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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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© Copyright Pearson Prentice Hall
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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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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Practice Problems for Sample Problem 10.10
Problem Solving 10.34 Solve
Problem 34 with the help of an
interactive guided tutorial.
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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.
10.3
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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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Practice Problems for Sample Problem 10.11
Problem-Solving 10.37 Solve
Problem 37 with the help of an
interactive guided tutorial.
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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.
10.3
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Percent Composition and
Chemical Formulas > Molecular Formulas 10.3
Methanal, ethanoic acid,
and glucose all have the
same empirical formula—
CH2O.
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Percent Composition and
Chemical Formulas > Molecular Formulas 10.3
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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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Percent Composition and
Chemical Formulas > Concept Map 10
Concept Map 10 Solve the
Concept Map with the help of
an interactive tutorial.
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