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1.3 Molecular Formulas and Percent Composition (Solution, Pt. 1)

Lesson Summary

1. The empirical formula of a compound with molecules containing 12 carbon atoms, 14 hydrogen atoms, and 6 oxygen atoms is __________.

A. C12H14O6

B. C6H7O3

C. CHO

D. CH2O

E. C2H4O

2. Calculate the percent composition, by mass, of carbon in the following compounds:

Cocaine, C17H21NO4

Vancomycin, C55H75Cl2N9O24

3. What is the molecular formula of each of the following compounds?

Empirical formula CH2, molar mass = 84 g/mol

Empirical formula HCO2, molar mass = 90.0 g/mol

4. What is the empirical formula of a compound with 9.5% C, 12.7% O, and 56.3% Cl?

A. COCl
B. COCl2
C. C2OCl
D. CO2Cl
E. ClCO4

5. Which of the following ores containing Cu (63.5 g/mol) has the highest percentage of Cu by mass? (The molar masses are given inside the parenthesis.)

A. Chalcopyrite, CuFeS2 (183.5 g/mol)
B. Chalcocite, Cu2S (159 g/mol)
C. Covellite, CuS (95.6 g/mol)
D. Cuprite, Cu2O (143 g/mol)
E. Tenorite, CuO (79.5 g/mol)

6. An ore containing gold was processed so that all of the gold is converted to AuCl3 (303 g/mol). If a 4.0 g sample of an ore produced 3.03 g of AuCl3, what is the percentage of Au (197 g/mol) in the ore?

A. 10.0 %
B. 49.3 %
C. 75.8 %
D. 98.5 %
E. 24.6 %