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Practice Test Stoichiometry
AP Chemistry
1.) What is the mass of 4 atom(s) of copper in grams?
A) 254.2 g
B) 2.37  1021 g
C) 9.57  10–24 g
D) 6.022  1023 g
E) 4.22  10–22 g
2.) A sample of ammonia has a mass of 43.5 g. How many molecules are in this sample?
A) 2.55 molecules
B) 2.62  1025 molecules
C) 2.36 1023 molecules
D) 1.54  1024 molecules
E) 8.63  10–16 molecules
3.) Roundup, an herbicide manufactured by Monsanto, has the formula C3H8NO5P. How
many moles of molecules are there in a 295.1-g sample of Roundup?
A) 0.5729
B) 2.137
C) 1.745
D) 16.39
E) none of these
4.) Phosphorus has the molecular formula P4, and sulfur has the molecular formula S8. How
many grams of phosphorus contain the same number of molecules as 4.23 g of sulfur?
A) 2.04 g
B) 0.490 g
C) 4.08 g
D) 4.23 g
E) none of these
5.) A given sample of a xenon fluoride compound contains molecules of a single type XeFn,
where n is some whole number. Given that 8.06  1020 molecules of XeFn weigh 0.227 g,
calculate n.
A) 1
B) 6
C) 4
D) 3
E) 2
6.) Phosphoric acid can be prepared by reaction of sulfuric acid with “phosphate rock”
according to the equation:
Ca3(PO4)2 + 3H2SO4  3CaSO4 + 2H3PO4
How many oxygen atoms are there in 1.75 ng of Ca3(PO4)2?
A) 3.40  1012
B) 1.36  1013
C) 8.43  1015
D) 2.72  1022
E) 2.72  1013
7.) How many atoms of hydrogen are present in 7.63 g of ammonia?
A) 2.70  1023
B) 1.52  1024
C) 1.38  1025
D) 8.09  1023
E) 1.12  1020
8.) One molecule of a compound weighs 2.93  10–22 g. The molar mass of this compound
A) 2.06 g/mol
B) 567 g/mol
C) 168 g/mol
D) 176 g/mol
E) none of these
9.) A compound is composed of element X and hydrogen. Analysis shows the compound to
be 80% X by mass, with three times as many hydrogen atoms as X atoms per molecule.
Which element is element X?
A) He
B) C
C) F
D) S
E) none of these
10.) A substance contains 35.0 g nitrogen, 5.05 g hydrogen, and 60.0 g of oxygen. How
many grams of hydrogen are there in a 153-g sample of this substance?
A) 7.72 g
B) 767 g
C) 15.4 g
D) 5.05 g
E) 30.3 g
11.) A mixture of KCl and KNO3 is 44.20% potassium by mass. The percentage of KCl in
the mixture is closest to
12.) Each molecule of testosterone contains 19 atoms of carbon (plus other atoms). The mass
percent of carbon in testosterone is 79.12%. What is the molar mass of testosterone?
576.8 g/mol
180.5 g/mol
228.2 g/mol
240.1 g/mol
288.4 g/mol
13.) Which of the following compounds has the same percent composition by mass as
styrene, C8H8?
A) acetylene, C2H2
B) benzene, C6H6
C) cyclobutadiene, C4H4
D) -ethyl naphthalene, C12H12
E) all of these
14.) You take an aspirin tablet (a compound consisting solely of carbon, hydrogen, and
oxygen) with a mass of 1.00 g, burn it in air, and collect 2.20 g of carbon dioxide and
0.400 g water. The molar mass of aspirin is between 170 and 190 g/mol. The molecular
formula of aspirin is
none of these
15.) Suppose you are given the percent by mass of the elements in a compound and you wish
to determine the empirical formula. Which of the following is true?
You must convert percent by mass to relative numbers of atoms.
You must assume exactly 100.0 g of the compound.
You must divide all of the percent by mass numbers by the smallest percent by
You cannot solve for the empirical formula without the molar mass.
At least two of the above (A-D) are true.
16.) A chloride of rhenium contains 63.6% rhenium. What is the formula of this compound?
A) ReCl
B) ReCl3
C) ReCl5
D) ReCl7
E) Re2Cl3
17.) A hydrocarbon (a compound consisting solely of carbon and hydrogen) is found to be
85.6% carbon by mass. What is the empirical formula for this compound?
B) CH2
C) C2H
D) C3H
E) CH4
18.) The empirical formula of a group of compounds is CHCl. Lindane, a powerful
insecticide, is a member of this group. The molar mass of lindane is 290.8 g/mol. How
many atoms of carbon does a molecule of lindane contain?
A) 2
B) 3
C) 4
D) 6
E) 8
19.) Vitamin C contains the elements C, H, and O. It is known to contain 40.9% C and
4.58% H by mass. The molar mass of vitamin C has been found to be about 180 g/mol.
The molecular formula for vitamin C is:
A) C2H3O2
B) C3H4O3
C) C4H6O4
D) C6H8O6
E) C14H18
20.) A 0.4987-g sample of a compound known to contain only carbon, hydrogen, and oxygen
was burned in oxygen to yield 0.9267 g of CO2 and 0.1897 g of H2O. What is the
empirical formula of the compound?
B) C2H2O
C) C3H3O2
D) C6H3O2
E) C3H6O2
21.) How many of the following are true concerning balanced chemical equations?
I. The number of molecules is conserved.
II. The coefficients for the reactants tell you how much of each reactant you are given.
III. Atoms are neither created nor destroyed.
IV. The coefficients indicate the mass ratios of the substances used.
V. The sum of the coefficients on the reactant side equals the sum of the coefficients on
the product side.
22.) In balancing an equation, we change the __________ to make the number of atoms on
each side of the equation balance.
A) formulas of compounds in the reactants
B) coefficients of compounds
C) formulas of compounds in the products
D) subscripts of compounds
E) none of these
23.) What is the coefficient for oxygen when the following equation is balanced?
NH3(g) + O2(g)  NO2(g) + H2O(g)
A) 3
B) 6
C) 7
D) 12
E) 14
24.) What is the sum of the coefficients of the following equation when it is balanced using
smallest whole numbers?
NaNH2 + NaNO3  NaN3 +NaOH + NH3
A) 5
B) 6
C) 7
D) 8
E) 9
25.) Indium reacts with chlorine to form InCl3. In the balanced equation for this reaction, the
coefficient of the indium trichloride is
A) 1
B) 2
C) 3
D) 4
E) 6
26.) The correct coefficients to balance the following reaction are, in order:
I2O5 + H2S  I2 + SO2 + H2O
A) 1, 1, 1, 1, 1
B) 1, 2, 1, 2, 1
C) 2, 4, 1, 4, 5
D) 2, 5, 2, 5, 5
E) 3, 5, 3, 5, 5
27.) A reaction occurs between sodium carbonate and hydrochloric acid producing sodium
chloride, carbon dioxide, and water. The correct set of coefficients, respectively, for the
balanced reaction is:
A) 3 6 6 3 4
B) 8 6 5 10 5
C) 5 10 10 5 5
D) 1 2 2 1 1
E) none of these
28.) You heat 3.869 g of a mixture of Fe3O4 and FeO to form 4.141 g Fe2O3. The mass of
oxygen reacted is
A) 0.272 g
B) 0.476 g
C) 1.242 g
D) 1.000 g
E) none of these
29.) The Claus reactions, shown below, are used to generate elemental sulfur from hydrogen
2H2S + 3O2  2SO2 + 2H2O
SO2 + 2H2S  3S + 2H2O
How much sulfur (in grams) is produced from 21.5 grams of O2?
A) 97.0 g
B) 14.4 g
C) 21.5 g
D) 43.1 g
E) none of these
30.) When 233.1 g of ethylene (C2H4) burns in oxygen to give carbon dioxide and water,
how many grams of CO2 are formed?
A) 731.4 g
B) 365.7 g
C) 182.9 g
D) 8.31 g
E) 299.4 g
31.) What would be the g Al / mole S ratio for the product of a reaction between aluminum
and sulfur?
A) 26.98 g Al / mol S
B) 80.94 g Al / mol S
C) 40.47 g Al / mol S
D) 53.96 g Al / mol S
E) 17.99 g Al / mol S
32.) How many grams of Ca(NO3)2 can be produced by reacting excess HNO3 with 6.33 g of
A) 7.01 g
B) 14.0 g
C) 28.0 g
D) 12.7 g
E) 6.33 g
33.) Iron is produced from its ore by the reactions:
How many moles of O2(g) are needed to produce 4.6 moles of Fe(s)?
A) 2.3 mole O2
B) 3.5 mole O2
C) 4.6 mole O2
D) 6.9 mole O2
E) 13.8 mole O2
34.) The refining of aluminum from bauxite ore (which contains 50.% Al2O3 by mass)
proceeds by the overall reaction 2Al2O3 + 3C  4Al + 3CO2. How much bauxite ore is
required to give the 5.0  1013 g of aluminum produced each year in the United States?
(Assume 100% conversion.)
A) 1.3  1013 g
B) 5.3  1013 g
C) 1.9  1014 g
D) 7.6  1014 g
E) none of these
35.) One commercial system removes SO2 emissions from smoke at 95.0°C by the following
set of balanced reactions:
SO2 + Cl2  SO2Cl2
SO2Cl2 + 2H2O  H2SO4 + 2HCl
H2SO4 + Ca(OH)2  CaSO4 + 2H2O
Assuming the process is 95.0% efficient, how many grams of CaSO4 may be produced
from 100. grams of SO2?
(molar masses: SO2, 64.1 g/mol; CaSO4, 136 g/mol)
A) 44.8 g
B) 47.1 g
C) 87.2 g
D) 202 g
E) 212 g
36.) The following two reactions are important in the blast furnace production of iron metal
from iron ore (Fe2O3):
Using these balanced reactions, how many moles of O2 are required for the production
of 3.19 kg of Fe?
A) 42.8 moles
B) 19.0 moles
C) 171 moles
D) 57.1 moles
E) 2.39 moles
37.) The limiting reactant in a reaction
A) has the lowest coefficient in a balanced equation
B) is the reactant for which you have the fewest number of moles
C) has the lowest ratio of moles available/coefficient in the balanced equation
D) has the lowest ratio of coefficient in the balanced equation/moles available
E) none of these
38.) Suppose the reaction Ca3(PO4)2 + 3H2SO4  3CaSO4 + 2H3PO4 is carried out starting
with 153 g of Ca3(PO4)2 and 76.8 g of H2SO4. How much phosphoric acid will be
A) 76.7 g
B) 51.1 g
C) 229.8 g
D) 115.1 g
E) 96.7 g
39.) Phosphorus, P4, can be prepared from calcium phosphate by the reaction
3370 g
1795 g
650 g
2Ca3(PO4)2 +
310 g/mol
60.1 g/mol
 6CaSiO3 + P4 + 10CO
12.0 g/mol
The molar mass for each reactant is shown below the reactant, and the mass of each
reactant for this problem is given above. Which reactant is the limiting reagent?
A) C
B) SiO2
C) Ca3(PO4)2
D) P4
E) More information is needed.
40.) Consider the fermentation reaction of glucose:
A 1.00-mole sample of C6H12O6 was placed in a vat with 100 g of yeast. If 32.3 grams
of C2H5OH was obtained, what was the percent yield of C2H5OH?
A) 35.1%
B) 17.5%
C) 100%
D) 32.3%
E) none of these
41.) When 20.0 g C2H6 and 60.0 g O2 react to form CO2 and H2O, how many grams of water
are formed?
A) 14.5 g
B) 18.0 g
C) 58.0 g
D) 20.0 g
E) none of these
42.) Which of the following statements is always true concerning a reaction represented by
the following balanced chemical equation?
2C2H6(g) + 7O2(g)  6H2O(l) + 4CO2(g)
A) If we have equal masses of C2H6 and O2, there is no limiting reactant.
B) If we have an equal number of moles of C2H6 and O2, there is no limiting reactant.
C) If we have more mass of C2H6, then O2 must be limiting.
D) If we have more mass of O2, then C2H6 must be limiting.
E) None of these statements are true.
43.) If 45.0 g of O2 are mixed with 45.0 g of H2 and the mixture is ignited, what mass of
water is produced?
A) 45.0 g
B) 50.7 g
C) 79.9 g
D) 25.3 g
E) 90.0 g
44.) Ammonia can be made by reaction of water with magnesium nitride as shown by the
following unbalanced equation:
Mg3N2(s) + H2O(l)  Mg(OH)2(s) + NH3(g)
If this process is 80% efficient, what mass of ammonia can be prepared from 19.0 kg
magnesium nitride?
A) 2.6 kg NH3
B) 6.4 kg NH3
C) 5.1 kg NH3
D) 3.2 kg NH3
E) 15 kg NH3
45.) One of the major commercial uses of sulfuric acid is in the production of phosphoric
acid and calcium sulfate. The phosphoric acid is used for fertilizer. The reaction is
Ca3(PO4)2 + 3H2SO4  3CaSO4 + 2H3PO4. What mass of concentrated H2SO4 (98% by
mass) must be used to react completely with 100.00 g of calcium phosphate?
46.) In a metallurgical process the mineral pyrite, FeS2, is roasted in air:
FeS2 + O2  Fe2O3 + SO2
The SO2 is then converted into H2SO4 in the following reactions:
2SO2 + O2  2SO3
SO3 + H2SO4  H2S2O7
H2S2O7 + H2O  2H2SO4
Assuming the mineral is 24.0% FeS2 and the remainder is inert, what mass of H2SO4 is
produced if 155 g of the mineral is used?
47.) Calculate the number of nitrogen atoms in 240. g of ammonium nitrate.
A) 2.01 x 1023 nitrogen atoms
B) 6.02 x 10 23 nitrogen atoms
C) 1.20 x 1024 nitrogen atoms
D) 1.81 x 1024 nitrogen atoms
E) 3.61 x 1024 nitrogen atoms
48.) An unknown molecule is found to consist of 24.2% carbon by mass, 4.0% hydrogen by
mass and the remaining mass is due to chlorine. What is the molecular formula of the
molecule given that the molar mass is found to be approximately 150?
A) CH2Cl
B) C2H4Cl2
C) CH2Cl4
D) C3H6Cl3
E) C6H10Cl2
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