AP Chemistry
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1  Problem Set: Chapter 2 Review Problems
Stoichiometry, Empirical Formulas, % Composition
1) What mass, in grams, should be weighed for an experiment that requires 1.72 mol
(NH4)2HPO4?
227 g
2) A. How many formula units are contained in 180.5 grams of K2CrO4?
5.597 x 1023 formula units
b. How many potassium ions?
1.119 x 1024 potassium ions
c. How many atoms of all kinds?
3.918 x 1024 atoms
3) A sample of propane C3H8 has the same mass as 10.0 million molecules of methane CH4
a. What is the mass of 10.0 million molecules of methane?
2.67 x 10-16 g
b. How many propane molecules does the sample contain?
3.64 x 106 Propane molecules
4) The beta-blocker drug, timolol, is expected to reduce the need for heart bypass surgery. Its
composition by mass is 49.4% C, 7.64% H, 17.7% N, 15.2% O, 10.1% S. The mass of 010100
mol of timolol is 3.16 g.
a. What is the simplest formula of timolol? (Use the format C#H#N#O#S# where #
indicate the subscripts)
C13H24N4O3S1
b. What is the molecular formula of timolol?
C13H24N4O3S1
5) Calculate the percent composition (by mass) of aspirin C9H8O4.
59.99. %C
4.48 %H
35.53%O
6) Ammonium nitrate, NH4NO3, and urea, CH4N2O, are both commonly used as sources of
nitrogen in commercial fertilizers. If ammonium nitrate sells for $2.95/lb, which has the more
nitrogen for the dollar?
a. Ammonium nitrate or urea
b. What is the difference between the two (in lb N/$) (give absolute value)
0.009 lb N/$
7) A metal, M, forms an oxide having the simples formula M2O3. This oxide contains 52.9% of
the metal by mass. Calculate the atomic weight of the metal.
27.0 g/mol
8) When a sample is burned in a combustion train, the percent oxygen in the sample cannot be
determined directly from the mass of water and carbon dioxide formed. Why?
In a combustion train, air is added to burn the hydrocarbon, thus much of the oxygen in the
water and carbon dioxide is from oxygen added for the combustion.
9) What mass of NaCl would contain the same total number of ions as 245 g of MgCl2?
226 g NaCl
10) What weight of magnesium carbonate is contained in 375 pounds of an ore that is 12.5%
magnesium carbonate by weight?
46.9 lbs.
a. What weight of impurities is contained in the sample?
328 lbs
b. What weight of magnesium is contained in the sample (assuming that none of the
impurities contain magnesium)?
13.5 lbs
11) A 1.20 g sample of a compound gave 2.92 g CO2 and 1.22 g of H2O on combustion in
oxygen. The compound is known to contain only carbon, hydrogen, and oxygen. What is its
simplest formula? (Use the format C#H#O#)
C4H8O1