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AP Chemistry
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2  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?
2) A. How many formula units are contained in
180.5 grams of K2CrO4?
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)
b. How many potassium ions?
b. What is the molecular formula of
timolol?
c. How many atoms of all kinds?
5) Calculate the percent composition (by
mass) of aspirin C9H8O4.
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?
6) Ammonium nitrate, NH4NO3, and urea,
b. How many propane molecules does the
sample contain?
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)
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.
10) What weight of magnesium carbonate is
contained in 375 pounds of an ore that is
12.5% magnesium carbonate by weight?
a. What weight of impurities is contained
in the sample?
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?
b. What weight of magnesium is
contained in the sample (assuming
that none of the impurities contain
magnesium)?
11) A 1.20 g sample of a compound gave
9) What mass of NaCl would contain the
same total number of ions as 245 g of
MgCl2?
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#)