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Chapter 7: Chemical Composition – Study Guide
*Do not forget about the extra resources available to help you study and prepare for this test!
 Textbook pages 167 – 203
 Mastering Chemistry Study Area: http://www.pearsonmylabandmastering.com/northamerica/
 Miss Marnik’s Website: http://www.northallegheny.org/Page/16665
 Labs, problem packets, and homework assignments
Section 1 – Measuring Matter: (text pages 168-170)
Need to be able to:
 Recognize that we use the mass of atoms to count them because they are too small to count
individually.
 Convert between moles and number of atoms.
Practice Problems:
1. Rank the quantities in order from smallest to largest:
a. 0.5 mol
b. 200
c. 5
d. 6,000,000,000
e. 6.02 x 1023
2. A silver ring contains 1.1 x 1022 silver atoms. How many moles of silver are in the ring?
3. How many moles of atoms are in 4.41 x 1023 K atoms?
4. How many gold atoms are in a pure gold ring containing 8.83 x 10-2 mol Au?
5. How many atoms are in 22.9 mol of mercury?
Section 2 – Formula Mass: (text pages 150-151)
Need to be able to:
 Calculate formula mass.
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Practice Problems
6. Calculate the formula mass of each of the following compounds. (Don’t forget your units!)
a. HNO3
c. Sr(NO3)2
b. CaBr2
d. Fe2(SO4)3
Section 3 – Mass and the Mole: (text pages 170-174)
Need to be able to:
 Convert between grams and moles.
 Convert between grams and number of atoms.
Practice Problems:
7. Find the molar mass of the following elements:
a. Hydrogen
c. Fluorine
b. Zinc
e. Barium
d. Argon
f.
Tungsten
8. Find the number of moles in each of the following samples:
a. 23.0 g of zinc
c. 24.9 g of argon
b. 38.1 g of tin
d. 0.0223 g of lithium
9. Calculate the mass of each sample:
a. 6.64 mol W
c. 0.581 mol Ba
b. 68.1 mol Xe
d. 1.57 mol S
Honors Chemistry
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10. How many atoms are in each of the following samples:
a. 16.9 g Sr
c. 8.55 g Bi
b. 26.1 g Fe
d. 38.2 g P
11. Calculate the mass in grams of each sample:
a. 1.32 x 1020 uranium atoms
c. 4.11 x 1023 lead atoms
b. 2.55 x 1022 zinc atoms
d. 6.59 x 1024 silicon atoms
Section 4 – Moles of Compounds: (text pages 174-181)
Need to be able to:
 Convert between grams and moles of a compound.
 Convert between mass of a compound and number of molecules.
 Convert between moles of a compound and moles of a constituent element.
 Convert between grams of a compound and grams of a constituent element.
Practice Problems:
12. How many moles of each element are in 1.00 mole of trichloromethane (CHCl3)?
a. How many atoms of chlorine are in 1.00 mol of trichloromethane?
b. How many atoms of chlorine are in 3.00 mol of trichloromethane?
13. Determine the number of moles of Cl in 2.7 mol CaCl2.
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14. Determine the number of moles of C in 5.67 mol C4H10.
15. Determine the molar mass of each of the following compounds:
a. CO2
c. CFCl3
b. HgF
d. Copper (II) cyanide
16. Find the number of moles of each compound:
a. 38.2 g sodium chloride
c. 4.25 g carbon dioxide
b. 36.5 g nitrogen monoxide
d. 2.71 g carbon tetrachloride
17. Determine the mass of each sample:
a. 1.32 mol carbon tetrafluoride
c. 1.29 mol carbon disulfide
b. 0.555 mol magnesium fluoride
d. 1.89 mol sulfur trioxide
18. Determine the number of molecules in each sample:
a. 3.5 g H2O
c. 89 g CCl4
b. 56.1 g N2
d. 19 g C6H12O6
Honors Chemistry
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19. Calculate the mass in grams of each sample:
a. 5.94 x 1020 H2O2 molecules
c. 4.5 x 1025 O3 molecules
b. 2.8 x 1022 SO2 molecules
d. 9.85 x 1019 CH4 molecules
Section 5 – Empirical and Molecular Formulas: (text pages 182-189)
Need to be able to:
 Determine mass percent composition from a chemical formula.
 Determine an empirical formula from experimental data.
 Calculate an empirical formula from reaction data.
 Calculate a molecular formula from an empirical formula and molar mass.
Practice Problems:
20. What is the percent composition of sodium phosphate?
a. How many grams of Na
are in 145 g of sodium
phosphate?
b. How many grams of P
are in 25 g of sodium
phosphate?
c. How many grams of O
are in 185 g of sodium
phosphate?
21. What is the percent composition of hydrochloric acid?
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22. What is the empirical formula of the following substances?
a. H2O2
b. C6H12O6
c. CH3O
d.
C2H4O2
23. Determine the empirical formula for a compound containing 2.128 g of Cl and 1.203 g of Ca.
24. A compound weighing 298.12 g consists of 72.2% magnesium and 27.8% nitrogen by mass. What is the
empirical formula?
25. Find the molecular formula for a compound whose molar mass is ~124.06 g/mole and whose empirical
formula is CH2O3.
26. Find the molecular formula for a compound that contains 4.90 g N and 11.2 g O. The molar mass of the
compound is 92.0 g/mol.
27. A 528.39 g compound containing only carbon, hydrogen, and oxygen is found to be 48.38% carbon and
8.12% hydrogen by mass. The molar mass of this compound is known to be ~222.25 g/mol. What is its
molecular formula?