Chapter10 section03 Percent Composition and Chemical Formulas By Hamdy Karim.
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Slide 1 of 40
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Percent Composition and Chemical Formulas
> The Percent Composition of a Compound
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
I. Percent Composition from Mass Data
10.3
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SAMPLE PROBLEM
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10.9
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SAMPLE PROBLEM
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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
II. Percent Composition from the Chemical Formula
10.3
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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
> Empirical Formulas
Empirical Formulas
The empirical formula gives the lowest whole-number ratio of the atoms of the elements in a 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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Percent Composition and Chemical Formulas
>
Rules for Determining Empirical Formula:
1.Convert grams of each element to moles
2.Divide each # of moles by the smallest # of moles
3.If answers to #2 are not all whole numbers, multiply by integers (2, 3…) to get whole numbers
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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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Practice Problems
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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
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 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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Percent Composition and Chemical Formulas
>
Steps to Determining the Molecular Formula of a Compound:
1.Determine the empirical formula
2.Find the molar mass of the empirical formula
3.Divide the molecular formula mass (given in problem) by the empirical formula mass (from step 2)
4.Multiply this integer by the empirical formula
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SAMPLE PROBLEM
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10.12
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SAMPLE PROBLEM
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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.
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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.
END OF SHOW