Chem 112 – Stoichiometry Practice Test
Matching
Match each item with the correct statement below.
a. actual yield
e.
b. percent yield
f.
c. theoretical yield
g.
d. excess reagent
h.
limiting reagent
mass
number of molecules
volume
____
1. This quantity can always be used in the same way as moles when interpreting balanced chemical equations.
____
2. This is conserved only in reactions where the temperature is constant and the number of moles of gaseous
reactants is the same as that of gaseous products.
____
3. This is conserved in every ordinary chemical reaction.
____
4. the reactant that determines the amount of product that can be formed in a reaction
____
5. the maximum amount of product that could be formed from given amounts of reactants
____
6. the reactant that is not completely used up in a reaction
____
7. the amount of product formed when a reaction is carried out in the laboratory
____
8. the ratio of the actual yield to the theoretical yield
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
9. How many hydrogen atoms are in 5 molecules of isopropyl alcohol, C H O?
a. 5 (6.02 10 )
c. 35
b. 5
d. 35 (6.02 10 )
____ 10. Avogadro's number of representative particles is equal to one ____.
a. kilogram
c. kelvin
b. gram
d. mole
____ 11. All of the following are equal to Avogadro's number EXCEPT ____.
a. the number of atoms of bromine in 1 mol Br
b. the number of atoms of gold in 1 mol Au
c. the number of molecules of nitrogen in 1 mol N
d. the number of molecules of carbon monoxide in 1 mol CO
____ 12. How many molecules are in 2.10 mol CO ?
a. 2.53 10 molecules
b. 3.79 10 molecules
c. 3.49
d. 1.26
____ 13. What is the molar mass of (NH ) CO ?
a. 144 g/mol
b. 138 g/mol
c. 96 g/mol
d. 78 g/mol
10
10
____ 14. What is the mass of oxygen in 250 g of sulfuric acid, H SO ?
a. 0.65 g
c. 16 g
b. 3.9 g
d. 160 g
molecules
molecules
____ 15. What is the volume, in liters, of 0.500 mol of C H gas at STP?
a. 0.0335 L
c. 16.8 L
b. 11.2 L
d. 22.4 L
____ 16. What is the density at STP of the gas sulfur hexafluoride, SF ?
a. 0.153 g/L
c. 3270 g/L
b. 6.52 g/L
d. 3.93 10 g/L
____ 17. Which of the following gas samples would have the largest number of representative particles at STP?
a. 12.0 L He
c. 0.10 L Xe
b. 7.0 L O
d. 0.007 L SO
____ 18. If the density of a noble gas is 1.783 g/L at STP, that gas is ____.
a. Kr
c. Ar
b. Xe
d. He
____ 19. What is the percent composition of chromium in BaCrO ?
a. 4.87%
c. 20.5%
b. 9.47%
d. 25.2%
____ 20. Which of the following compounds has the highest oxygen content, by weight?
a. Na O
c. BaO
b. CO
d. H O
____ 21. The lowest whole-number ratio of the elements in a compound is called the ____.
a. empirical formula
c. binary formula
b. molecular formula
d. representative formula
____ 22. Which of the following is true about the total number of reactants and the total number of products in the
reaction shown below?
C H (l) + 8O (g)  5CO (g) + 6H O(g)
a. 9 moles of reactants chemically change into 11 moles of product.
b. 9 grams of reactants chemically change into 11 grams of product.
c. 9 liters of reactants chemically change into 11 liters of product.
d. 9 atoms of reactants chemically change into 11 atoms of product.
____ 23. Which of the following is an INCORRECT interpretation of the balanced equation shown below?
2S(s) + 3O (g)  2SO (g)
a. 2 atoms S + 3 molecules O  2 molecules SO
b. 2 g S + 3 g O  2 g SO
c. 2 mol S + 3 mol O  2 mol SO
d. none of the above
____ 24. How many moles of glucose, C H O , can be "burned" biologically when 10.0 mol of oxygen is available?
C H O (s) + 6O (g)  6CO (g) + 6H O(l)
a. 0.938 mol
c. 53.3 mol
b. 1.67 mol
d. 60.0 mol
____ 25. At STP, how many liters of oxygen are required to react completely with 3.6 liters of hydrogen to form
water?
2H (g) + O (g)  2H O(g)
a. 1.8 L
c. 2.0 L
b. 3.6 L
d. 2.4 L
____ 26. The equation below shows the decomposition of lead nitrate. How many grams of oxygen are produced when
11.5 g NO is formed?
a. 1.00 g
b. 2.00 g
c. 2.88 g
d. 32.0 g
____ 27. When glucose is consumed, it reacts with oxygen in the body to produce carbon dioxide, water, and energy.
How many grams of carbon dioxide would be produced if 45 g of C H O completely reacted with
oxygen?
a. 1.5 g
c. 11 g
b. 1.8 g
d. 66 g
____ 28. Which of the following is NOT true about limiting and excess reagents?
a. The amount of product obtained is determined by the limiting reagent.
b. A balanced equation is necessary to determine which reactant is the limiting reagent.
c. Some of the excess reagent is left over after the reaction is complete.
d. The reactant that has the smallest given mass is the limiting reagent.
____ 29. Identify the limiting reagent and the volume of CO formed when 11 L CS reacts with 18 L O to produce
CO gas and SO gas at STP.
CS (g) + 3O (g)
CO (g) + 2SO (g)
a. CS ; 5.5 L CO
c. CS ; 11 L CO
b. O ; 6.0 L CO
d. O ; 27 L CO
____ 30. What is the maximum number of grams of PH that can be formed when 6.2 g of phosphorus reacts with 4.0
g of hydrogen to form PH ?
P (g) + 6H (g)
4PH (g)
a. 0.43 g
c. 270 g
b. 6.8 g
d. 45 g
____ 31. Methane and hydrogen sulfide form when hydrogen reacts with carbon disulfide. Identify the excess reagent
and calculate how much remains after 36 L of H reacts with 12 L of CS .
4H (g) + CS (g)
CH (g) + 2H S(g)
a. 3 L CS
c. 9 L CS
b. 6 L CS
d. 12 L H
____ 32. Hydrogen gas is produced when zinc reacts with hydrochloric acid. If the actual yield of this reaction is 85%,
how many grams of zinc are needed to produce 112 L of H at STP?
Zn(s) + 2HCl(aq)
ZnCl (s) + H (g)
a. 95 g
c. 280 g
b. 180 g
d. 380 g
Short Answer
33. Find the mass in grams of 3.10
10
molecules of F .
34. Calculate the molecular formulas of the compounds having the following empirical formulas and molar
masses: C H , 58 g/mol; CH, 78 g/mol; and HgCl, 236.1 g/mol.
35. If 8.00 mol of NH reacted with 14.0 mol of O , how many moles of H O will be produced?
4NH (g) + 7O (g)
4NO + 6H O(g)
36. If 5.0 g of H are reacted with excess CO, how many grams of CH OH are produced, based on a yield of
86%?
CO(g) + 2H (g)
CH OH(l)
37. For the reaction 2Na(s) + Cl (g)
Na and 13.0 L of Cl (at STP)?
2NaCl(s), how many grams of NaCl could be produced from 103.0 g of
38. The decomposition of potassium chlorate yields oxygen gas. If the yield is 95%, how many grams of KClO
are needed to produce 10.0 L of O ?
2KClO (s)
2KCl(s) + 3O (g)
Essay
39. The percentage composition of a polymer used for the non-stick surfaces of cooking utensils is 24% C and
76% F by mass. Explain the steps in determining the empirical formula of the polymer.
40. The density of acetylene at STP is 1.17 g/L. The empirical formula of acetylene is CH. Describe how you can
determine the molar mass of acetylene and its molecular formula if you know only its density at STP and its
empirical formula.
41. What is the importance of the coefficients in a balanced chemical reaction?
42. What is the general procedure for solving a stoichiometric problem?
43. Discuss reasons why the theoretical yield of a reaction is not the same as the actual yield.
Chem
Answer Section
MATCHING
1. ANS: G
PTS: 1
DIF: L1
REF: p. 356
OBJ: 12.1.2 Interpret balanced chemical equations in terms of interacting moles, representative particles,
masses, and gas volume at STP.
2. ANS: H
PTS: 1
DIF: L1
REF: p. 357
OBJ: 12.1.2 Interpret balanced chemical equations in terms of interacting moles, representative particles,
masses, and gas volume at STP.
3. ANS: F
PTS: 1
DIF: L1
REF: p. 357
OBJ: 12.1.2 Interpret balanced chemical equations in terms of interacting moles, representative particles,
masses, and gas volume at STP. | 12.1.3 Identify the quanties that are always conserved in chemical
reactions.
4. ANS: E
PTS: 1
DIF: L1
REF: p. 369
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
5. ANS: C
PTS: 1
DIF: L1
REF: p. 369
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
6. ANS: D
PTS: 1
DIF: L1
REF: p. 372
OBJ: 12.3.2 Calculate theoretical yield, actual yield, or percent yield given appropriate information.
7. ANS: A
PTS: 1
DIF: L1
REF: p. 372
OBJ: 12.3.2 Calculate theoretical yield, actual yield, or percent yield given appropriate information.
8. ANS: B
PTS: 1
DIF: L1
REF: p. 372
OBJ: 12.3.2 Calculate theoretical yield, actual yield, or percent yield given appropriate information.
MULTIPLE CHOICE
9. ANS: C
PTS: 1
DIF: L1
REF: p. 291 | p. 292
OBJ: 10.1.2 Relate Avogadro’s number to a mole of a substance.
10. ANS: D
PTS: 1
DIF: L1
REF: p. 290
OBJ: 10.1.2 Relate Avogadro’s number to a mole of a substance.
11. ANS: A
PTS: 1
DIF: L1
REF: p. 290
OBJ: 10.1.2 Relate Avogadro’s number to a mole of a substance.
12. ANS: D
PTS: 1
DIF: L2
REF: p. 291 | p. 292
OBJ: 10.1.2 Relate Avogadro’s number to a mole of a substance.
13. ANS: C
PTS: 1
DIF: L2
REF: p. 295 | p. 296
OBJ: 10.1.4 Describe how the mass of a mole of a compound is calculated.
14. ANS: D
PTS: 1
DIF: L2
REF: p. 298
OBJ: 10.2.1 Describe how to convert the mass of a substance to the number of moles of a substance, and
moles to mass.
15. ANS: B
PTS: 1
DIF: L2
REF: p. 301
OBJ: 10.2.2 Identify the volume of a quantity of gas at STP.
16. ANS: B
PTS: 1
DIF: L2
REF: p. 302
OBJ: 10.2.2 Identify the volume of a quantity of gas at STP.
17. ANS: A
PTS: 1
DIF: L3
REF: p. 301
OBJ: 10.2.2 Identify the volume of a quantity of gas at STP.
18. ANS: C
PTS: 1
DIF: L3
REF: p. 302
OBJ: 10.2.2 Identify the volume of a quantity of gas at STP.
19. ANS: C
PTS: 1
DIF: L2
REF: p. 307
OBJ: 10.3.1 Describe how to calculate the percent by mass of an element in a compound.
20. ANS: D
PTS: 1
DIF: L3
REF: p. 307
OBJ: 10.3.1 Describe how to calculate the percent by mass of an element in a compound.
21. ANS: A
PTS: 1
DIF: L1
REF: p. 309
OBJ: 10.3.2 Interpret an empirical formula.
22. ANS: A
PTS: 1
DIF: L2
REF: p. 356
OBJ: 12.1.2 Interpret balanced chemical equations in terms of interacting moles, representative particles,
masses, and gas volume at STP.
23. ANS: B
PTS: 1
DIF: L2
REF: p. 356
OBJ: 12.1.2 Interpret balanced chemical equations in terms of interacting moles, representative particles,
masses, and gas volume at STP.
24. ANS: B
PTS: 1
DIF: L2
REF: p. 359 | p. 360
OBJ: 12.2.1 Construct mole ratios from balanced chemical equations and apply these ratios in mole-mole
stoichiometric calculations.
25. ANS: A
PTS: 1
DIF: L1
REF: p. 363 | p. 364 | p. 365 | p. 366
OBJ: 12.2.2 Calculate stoichiometric quantities from balanced chemical equations using units of moles,
mass, representative particles, and volumes of gases at STP.
26. ANS: B
PTS: 1
DIF: L2
REF: p. 360 | p. 361 | p. 362
OBJ: 12.2.2 Calculate stoichiometric quantities from balanced chemical equations using units of moles,
mass, representative particles, and volumes of gases at STP.
27. ANS: D
PTS: 1
DIF: L2
REF: p. 360 | p. 361 | p. 362
OBJ: 12.2.2 Calculate stoichiometric quantities from balanced chemical equations using units of moles,
mass, representative particles, and volumes of gases at STP.
28. ANS: D
PTS: 1
DIF: L1
REF: p. 369
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
29. ANS: B
PTS: 1
DIF: L2
REF: p. 371
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
30. ANS: B
PTS: 1
DIF: L2
REF: p. 371
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
31. ANS: A
PTS: 1
DIF: L2
REF: p. 371
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
32. ANS: D
PTS: 1
DIF: L2
REF: p. 374
OBJ: 12.3.2 Calculate theoretical yield, actual yield, or percent yield given appropriate information.
SHORT ANSWER
33. ANS:
3.10 10 molecules
= 19.6 g F
1 mol F /6.02
10
molecules
38.0 g F /1 mol F
PTS: 1
DIF: L2
REF: p. 297
OBJ: 10.2.1 Describe how to convert the mass of a substance to the number of moles of a substance, and
moles to mass.
34. ANS:
58 g/mol/29 g/efm = 2 efm/mol; C H
78 g/mol/13 g/efm = 6 efm/mol; C H
236.1 g/mol/236.1 g/efm = 1 efm/mol; HgCl
PTS: 1
DIF: L3
REF: p. 312
OBJ: 10.3.3 Distinguish between empirical and molecular formulas.
35. ANS:
12.0 mol of H O
PTS: 1
DIF: L2
REF: p. 359
OBJ: 12.2.1 Construct mole ratios from balanced chemical equations and apply these ratios in mole-mole
stoichiometric calculations.
36. ANS:
Theoretical yield:
5.0 g H
1 mol H /2.0 g H
1 mol CH OH/2 mol H
32 g CH OH/1 mol CH OH
= 40 g CH OH
40 g CH OH 86% = 34 g CH OH
PTS: 1
DIF: L3
REF: p. 371
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
37. ANS:
13.0 L Cl
1 mol Cl /22.4 L Cl = 0.580 mol Cl
103.0 g Na 1 mol Na/23 g Na = 4.48 mol Na
Cl is limiting reagent: 0.580 mol Cl
2 mol NaCl/1 mol Cl = 1.16 mol NaCl
1.16 mol NaCl 58 g NaCl/1 mol NaCl = 67.3 g NaCl
PTS: 1
DIF: L3
REF: p. 371
OBJ: 12.3.1 Identify and use the limiting reagent in a reaction to calculate the maximum amount of
product(s) produced and the amount of excess reagent that remains unreacted.
38. ANS:
10.0 L 100%/95% = 10.5 L theoretical yield
10.5 L O
1 mol O /22.4 L O
2 mol KClO /3 mol O
122.6 g KClO /1mol KClO
= 38.4 g KClO
PTS: 1
DIF: L3
REF: p. 374
OBJ: 12.3.2 Calculate theoretical yield, actual yield, or percent yield given appropriate information.
ESSAY
39. ANS:
The quantity of each element present is given as a percent by mass, which means that for every 100 grams of
polymer there are 24 grams of C and 76 grams of F. The objective is to use the percentage mass quantities to
find the ratio of the moles of each element in the polymer. Begin by converting the number of grams to the
number of moles using a molar mass conversion factor. For example, 24 g C (1 mol C/12.0 g C) 2 mol C;
and 76.0 g F (1 mol F/19.0 g F) 4 mol F. Simplify the ratio 2 mol C/4 mol F 1 mol C : 2 mol F. Write
the empirical formula using the number of moles as subscripts, or CF .
PTS: 1
DIF: L3
REF: p. 310
OBJ: 10.2.1 Describe how to convert the mass of a substance to the number of moles of a substance, and
moles to mass. | 10.3.2 Interpret an empirical formula.
40. ANS:
Because the density of acetylene is determined at STP, the molar mass can be calculated. This is because
there are exactly 22.4 L of any gas present in 1 mol of that gas. Therefore, the molar mass of acetylene is:
(1.17 g/L) (22.4 L/mol) 26.2 g/mol. The empirical formula mass (efm) of acetylene as determined from
its empirical formula is 12.0 g C 1.0 g H = 13.0 g CH/mole CH. The molecular formula can then be
determined by dividing the molar mass by the efm, and multiplying the subscripts of the elements in the
empirical formula by this factor. For acetylene, molar mass/efm 26.2/13.0 2. Therefore, the molecular
formula is C H .
PTS: 1
DIF: L3
REF: p. 296 | p. 300 | p. 309 | p. 312
OBJ: 10.3.3 Distinguish between empirical and molecular formulas.
41. ANS:
The coefficients in a balanced chemical equation indicate the relative number of moles of reactants and
products. From this information, the amounts of reactants and products can be calculated. The number of
moles may be converted to mass, volume, or number of representative particles.
PTS: 1
DIF: L3
REF: p. 356
OBJ: 12.1.2 Interpret balanced chemical equations in terms of interacting moles, representative particles,
masses, and gas volume at STP.
42. ANS:
The coefficients from the balanced equation are used to write mole ratios. The mole ratios relate the moles of
reactants to the moles of product. By multiplying the number of moles of the reactant by the mole ratio, you
can determine the number of moles of the product.
PTS: 1
DIF: L2
REF: p. 359
OBJ: 12.2.1 Construct mole ratios from balanced chemical equations and apply these ratios in mole-mole
stoichiometric calculations.
43. ANS:
see p. 372-373
PTS: 1