PW51-EMPIRICAL FORMULAS
CHEM 110 (BEAMER)
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PRACTICE WORK 51: EMPIRICAL FORMULAS
General Information
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Do Date: W (5/4)
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You will need your calculator, the periodic table, and Appendix 11A.
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NOTE: I have revised Appendix 11a; you might want to print out the revised version.
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Reference Materials: Notes-63 (Beamer) and Chapter 8.8 (Textbook)
1A)
The percent composition of a compound is found to be 31.84% magnesium, 31.46% carbon, and 36.70% nitrogen. Determine the empirical formula for
this compound.
1B)
Use your answer to Question 1A to determine the empirical mass of the compound.
You do not need to show your work, but – if there is an error – showing work gives you partial credit
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PW51-EMPIRICAL FORMULAS
CHEM 110 (BEAMER)
2A)
The percent composition of a compound is found to be 29.73% iron, 19.18% carbon, and 51.10% oxygen. Determine the empirical formula for this
compound.
2B)
Use your answer to Question 2A to determine the empirical mass of the compound.
You do not need to show your work, but – if there is an error – showing work gives you partial credit
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PW51-EMPIRICAL FORMULAS
CHEM 110 (BEAMER)
3A)
Methyl acetoacetate is an organic compound with a fruity odor that is used as a flavoring in foods. A 180.0-gram sample is chemically separated into its
component elements: 93.08 g of carbon, 12.52 grams of hydrogen, and 74.40 grams of oxygen. Determine the empirical formula for this compound.
3B)
Use your answer to Question 3A to determine the empirical mass of the compound.
You do not need to show your work, but – if there is an error – showing work gives you partial credit
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PW51-EMPIRICAL FORMULAS
CHEM 110 (BEAMER)
4A)
Naphthalene is the main ingredient in mothballs that gives them their characteristic odor. The percent composition (by mass) of each element in
naphthalene is 93.7% carbon and 6.30% hydrogen. Determine the empirical formula for this substance.
4B)
Use your answer to Question 4A to determine the empirical mass of naphthalene.
You do not need to show your work, but – if there is an error – showing work gives you partial credit
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PW51-EMPIRICAL FORMULAS
CHEM 110 (BEAMER)
5A)
Slight Trick Question: Benzoic acid is an organic compound used in food preservatives. A 250.0-gram sample is separated into its individual elements
and found to contain 172.09 grams of carbon and 12.40 grams of hydrogen. The rest is oxygen. Determine the empirical formula for benzoic acid.
5B)
Use your answer to Question 5A to determine the empirical mass of benzoic acid.
You do not need to show your work, but – if there is an error – showing work gives you partial credit
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PW51-EMPIRICAL FORMULAS
CHEM 110 (BEAMER)
NOTE: Questions 6a and 6b would be “extra credit” questions.
6A)
Pentane is an organic liquid that is sometimes used in pesticides and in the production of polystyrene (styrofoam). Determine the empirical formula for
pentane if its composition is 83.21% carbon and 16.79% hydrogen by mass.
6B)
Use your answer to Question 6A to determine the empirical mass of pentane.
You do not need to show your work, but – if there is an error – showing work gives you partial credit
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PW51-EMPIRICAL FORMULAS
CHEM 110 (BEAMER)
Answer Key
1A)
MgC2N2
1B)
76.35 g/mol MgC2N2
2A)
FeC3O6
2B)
187.88 g/mol FeC3O6
3A)
C5H8O3
3B)
116.13 g/mol C5H8O3
4A)
C5H4
4B)
64.09 g/mol C5H4
5A)
C7H6O2
5B)
122.13 g/mol C7H6O2
6A)
C5H12
6B)
72.17 g/mol C5H12
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