Princeton 2012/Barron 4th ed.
AP Practice Problems
Unit 6 – Reactions & Stoichiometry
Multiple Choice (no calculator)
1. A hydrocarbon sample with a mass
of 6 grams underwent combustion
producing 11 grams of carbon
dioxide. If all of the carbon initially
present in the compound was
converted to carbon dioxide, what
was the percent of carbon, by mass,
in the hydrocarbon sample? (P5.5)
a.
b.
c.
d.
e.
25%
33%
50%
66%
75%
2. A sample of pure CaCO3 was heated
and decomposed according to the
reaction given below. If 28 grams of
CaO were produced by the reaction,
what was the initial mass of CaCO3?
(P5.10)
CaCO3(s)  CaO(s) + CO2(g)
a.
b.
c.
d.
e.
14 grams
25 grams
42 grams
50 grams
84 grams
3. Which of the following compounds
is soluble? (B4.5)
a.
b.
c.
d.
e.
MgCO3
Al(OH)3
Cr2S3
K2CrO4
NiSO3
4. Which of the following compounds
is insoluble? (B4.6)
a.
b.
c.
d.
e.
Ca(OH)2
Fe2S3
Na2CO3
H2SO3
AuCl3
5. When ammonium oxalate
(NH4)2C2O4, is dissolved in water,
the ions formed are (B4.8)
a. 2N-3(aq) + 8H+(aq) +
2C+4(aq) + 4O-2(aq)
b. (NH4)+2(aq) + C2O4-2(aq)
c. 2NH4+(aq) + C2O4-2(aq)
d. NH4+2(aq) + C2O4-2(aq)
e. 2NH4+(aq) + 2CO-2(aq)
6. When the combustion reaction for
benzene, C6H6, is properly balanced
with the smallest whole-number
coefficients possible, the sum of the
coefficients is (B4.10)
a.
b.
c.
d.
e.
15
4
35
17.5
12
Princeton 2012/Barron 4th ed.
7. Which of the following is a
replacement reaction? (B4.18)
a. sodium chloride with
potassium nitrate
b. chlorine gas with sodium
metal
c. aluminum metal with
hydrobromic acid
d. ethyl alcohol with oxygen
e. magnesium oxide with sulfur
trioxide
8. Which of the following is NOT true
of a net ionic equation? (B4.19)
a. All of the nonreacting ions
have been cancelled
b. It shows the actual reactants
in an equation
c. It allows the chemist to
substituted reactants in a
logical manner
d. It is used to determine which
compounds are insoluble
e. It must have the charges as
well as the atoms balanced
10. In the reaction below, how many
moles of aluminum will produce 1
mol of iron? (B6.12)
8Al + 3Fe3O4  9Fe + 4Al2O3
a.
b.
c.
d.
e.
1
3/4
9/8
8/9
4/3
11. A 0.200-g sample of a compound
containing only carbon, hydrogen,
and oxygen is burned, and 0.357 g of
CO2 and 0.146 g of H2O are
collected. What is the percentage of
carbon in this compound? (B6.18)
a.
b.
c.
d.
e.
56%
73%
48.7%
24.3%
43.2%
12. In the reaction
2AgNO3 + CaCl2  2AgCl + Ca(NO3)2
9. The wavelength of blue light is 400
nm. What is the wavelength in
centimeters? (B6.11)
a.
b.
c.
d.
e.
4.00×10-5 cm
400×10-9 cm
400×10-2 cm
2.5×106 cm
2.5×10-8 cm
how many grams of AgCl (molar
mass = 143.5) will precipitate when
20.0g AgNO3 (molar mass = 170) is
reacted with 15.0g CaCl2 (molar
mass = 111)? (B6.20)
a.
b.
c.
d.
e.
16.9
38.8
33.8
8.45
67.6
Princeton 2012/Barron 4th ed.
13. In the reaction
2AgNO3 + CaCl2  2AgCl + Ca(NO3)2
how many grams of which reactant
will remain when 20.0g AgNO3
(molar mass = 170) is reacted with
15.0g CaCl2 (molar mass = 111)?
(B6.21)
a.
b.
c.
d.
e.
6.53 g CaCl2
6.53 g AgNO3
45.9 g CaCl2
8.47 g CaCl2
25.9 g AgNO3
14. A 50.0-g sample of impure CaCl2 is
reacted with excess AgNO3
according to the reaction
2AgNO3 + CaCl2  2AgCl + Ca(NO3)2
If 5.86 g of AgCl (molar mass =
143.5) precipitates, what is the
percentage of chlorine (molar mass =
35.5) in the sample? (B6.22)
a.
b.
c.
d.
e.
1.45%
2.90%
3.80%
11.7%
8.53%
Princeton 2012/Barron 4th ed.
Essays
1. The table below shows three common forms of copper ore (P5.3).
Ore #
1
2
3
Empirical
Formula
Cu2S
?
?
Copper
?
34.6
55.6
Percent by Weight
Sulfur
?
34.9
28.1
Iron
?
30.5
16.3
a. What is the percent by weight of copper in Cu2S?
b. What is the empirical formula of ore #2?
c. If a sample of ore #3 contains 11.0 grams of iron, how many grams of sulfur does
it contain?
d. Cu can be extracted from Cu2S by the following process:
3 Cu2S + 3 O2  3 SO2 + 6 Cu
If 3.84 grams of O2 are consumed in the process, how many grams of Cu are
produced?
2. Answer the following questions considering the chemical and physical properties of ionic
substances. (B4.1)
a. A large majority of monatomic ions of the representative elements all have one
feature in common. What is that feature and give a specific example to illustrate
it.
b. Write the molecular equation, the ionic equation, and the net ionic equation for
the aqueous reaction of potassium chloride with lead nitrate. Indicate the phase of
each of the reactants and products.
c. What is the name for Cr(NO3)3 and what is the formula for copper (II) sulfate
pentahydrate?
d. What is the formula for the iodate ion?
Princeton 2012/Barron 4th ed.
3. The following questions involve stoichiometry problems frequently encountered by the
chemist in theoretical and laboratory situations. Use the appropriate stoichiometric
methods to answer the following questions. (B6.1)
a. One beaker holds a solution that contains 4.65 grams of sodium sulfide. A second
beaker holds a solution that contains 8.95 grams of lead (II) nitrate. When the
two solutions are mixed, what mass of precipitate forms?
b. Perform the calculations to determine the empirical formula of a CHNO
compound that is analyzed and found to contain 52.63 percent carbon, 7.02
percent hydrogen, and 12.28 percent nitrogen.
c. If the compound in part (b) has a molar mass of 228, what is the molecular
formula?
Princeton 2012/Barron 4th ed.
Answer Key Unit 6 – Reactions and Stoichiometry
Multiple Choice
1. C
2. D
3. D
4. B
5.
6.
7.
8.
C
C
C
D
9. A
10. D
11. C
12. A
13. D
14. B
Essay
1. (a) Molecular weight of Cu2S = 159.3 g
% by mass of Cu =
=
(b) Assume 100 grams of ore #2
34.6 g Cu / 63.6 = 0.544 / 0.544 = 1
30.5 g Fe / 55.9 = 0.546 / 0.544 = 1
34.9 g S / 32.1 = 1.09 / 0.544 = 2
Empirical Formula = CuFeS2
(c) 11 grams is 16.3% of the total molar mass so
11 = 0.163x where x = total molar mass
x = 67.5 grams
28.1% of 67.5 grams = 19.0 grams of sulfur
(d)
2. (a) Monatomic ions of the representative elements contain a single atom of an element in
the s-block or p-block of the periodic table. Most of these ions are formed by gaining or
losing electrons to become isoelectronic with its nearest noble gas. For example Ca loses
two electrons to become Ca+2.
(b) Molecular: 2KCl(aq) + Pb(NO3)2(aq)  PbCl2(s) + 2KNO3(aq)
Ionic: 2K+(aq) + 2Cl-(aq) + Pb+2(aq) + 2NO3-(aq)  PbCl2(s) + 2K+(aq) + 2NO3-(aq)
Net Ionic:
2Cl-(aq) + Pb+2(aq)  PbCl2(s)
(c) Chromium III nitrate and CuSO45H2O
(d) IO33. (a) Na2S(aq) + Pb(NO3)2(aq)  PbS(s) + 2NaNO3(aq)
Since there are two given amounts of products, perform a limiting reactant problem.
Princeton 2012/Barron 4th ed.
Therefore
is the limiting reactant so 6.47 grams of PbS are formed.
(b) Compound is CHNO so percent oxygen = 100% – 52.63 – 7.02 – 12.28 = 28.07 %
28.07 O / 16.0 = 1.75 / 0.877 = 2
52.62 C / 12.0 = 4.39 / 0.877 = 5
7.02 H / 1.00 = 7.02 / 0.877 = 8
12.28 N / 14.0 = 0.877 / 0.877 =1
Empirical formula = C5H8NO2
(c) 228/114 = 2 so C5H8NO2 × 2 = C10H16N2O4