Name ___________________________________ Date ________________ Class _______________
Unit 11 Test Review: Stoichiometry
Section 11.1 What is stoichiometry?
For each statement below, write true or false.
_______________ 1. The study of the quantitative relationships between the amounts of reactants
used and the amounts of products formed by a chemical reaction is
called stoichiometry.
_______________ 2. Stoichiometry is based on the law of conservation of mass.
_______________ 3. In any chemical reaction, the mass of the products is less than the mass of the
reactants.
_______________ 4. The coefficients in a chemical equation represent not only the number of
individual particles but also the number of moles of particles.
_______________ 5. The mass of each reactant and product is related to its coefficient in the
balanced chemical equation for the reaction by its molar mass.
Complete the table below, using information represented in the chemical equation for the combustion
of methanol, an alcohol.
methanol + oxygen → carbon dioxide + water
2CH3OH(l) + 3O2 (g) → 2CO2(g) + 4H2O(g)
Substance
Molar Mass
(g/mol)
6. Methanol
32.05
7. Oxygen gas
32.00
8. Carbon
dioxide
44.01
9. Water
18.02
Number of
Molecules
Number of
Moles (mol)
Mass (g)
10. What are the reactants? _________________________________________________________
11. What are the products? __________________________________________________________
12. What is the total mass of the reactants? _____________________________________________
13. What is the total mass of the products? _____________________________________________
14. How do the total masses of the reactants and products compare? ________________________
Answer the questions about the following chemical reaction.
sodium + iron(III) oxide → sodium oxide + iron
6Na(s) + Fe2O3(s) → 3Na2O(s) + 2Fe(s)
15. What is a mole ratio?
16. How is a mole ratio written?
17. Predict the number of mole ratios for this reaction. _______________
18. What are the mole ratios for this reaction?
19. What is the mole ratio relating sodium to iron? _________________________
20. What is the mole ratio relating iron to sodium? _________________________
21. Which mole ratio has the largest value? _________________________
Section 11.2 Stoichiometric Calculations
Read the following passage and then solve the problems. In the equation that follows each problem,
write in the space provided the mole ratio that can be used to solve the problem. Complete the
equation by writing the correct value on the line provided.
The reaction of sodium peroxide and water produces sodium hydroxide and oxygen gas. The following
balanced chemical equation represents the reaction.
2Na2O2(s) + 2H2O(l) → 4NaOH(s) + O2(g)
1. How many moles of sodium hydroxide are produced when 1.00 mol sodium peroxide reacts with water?
1.00 mol Na2O2 ×
= _______________ mol NaOH
2. How many moles of oxygen gas are produced when 0.500 mol Na2O2 reacts with water?
0.500 mol Na2O2 ×
= _______________ mol O2
3. How many moles of sodium peroxide are needed to produce 1.00 mol sodium hydroxide?
1.00 mol NaOH ×
= _______________mol Na2O2
4. How many moles of water are required to produce 2.15 mol oxygen gas in this reaction?
2.15 mol O2 ×
= _______________ mol H2O
5. How many moles of water are needed for 0.100 mol of sodium peroxide to react completely in this
reaction?
0.100 mol Na2O2 ×
= _______________ mol H2O
6. How many moles of oxygen are produced if the reaction produces 0.600 mol sodium hydroxide?
0.600 mol NaOH ×
= _______________ mol O2
Solving a mass-to-mass problem requires the four steps listed below. The equations in the boxes show
how the four steps are used to solve an example problem. After you have studied the example, solve
the problems below, using the four steps.
Example problem: How many grams of carbon dioxide are produced when 20.0 g acetylene (C2H2) is burned?
Step 1 Write a balanced chemical equation for the reaction.
Step 2 Determine the number of moles of the known
substance, using mass-to-mole conversion.
Step 3 Determine the number of moles of the unknown
substance, using mole-to-mole conversion.
Step 4 Determine the mass of the unknown substance, using
mole-to-mass conversion.
7. In some mole-to-mass conversions, the number of moles of the known substance is given. In those
conversions, which step of the above solution is not necessary? ____________________
8. In a blast furnace, iron and carbon monoxide are produced from the reaction of iron(III) oxide (Fe2O3)
and carbon. How many grams of iron are formed when 150 g iron(III) oxide reacts with an excess of
carbon?
9. Solid sulfur tetrafluoride (SF4) and water react to form sulfur dioxide and an aqueous solution of
hydrogen fluoride. How many grams of water are necessary for 20.0 g sulfur tetrafluoride to react
completely?
Section 11.3 Limiting Reactants
Study the diagram showing a chemical reaction and the chemical equation that represents the
reaction. Then complete the table keeping your answers in terms of the units provided for that row of
the table. Show your calculations for questions 25-27 in the space below the table.
The molar masses of O2, NO, and NO2 are 32.00 g/mol, 30.01 g/mol, and 46.01 g/mol, respectively.
***Keep your answers in terms of the units provided for that row of the table.***
Amount of
O2
Amount of
NO
Amount of NO2
Amount and Name
of Excess Reactant
Limiting Reactant
1 molecule
2 molecules
2 molecules
none
none
4 molecules
4 molecules
4 molecules
NO
2 molecules O2
2 molecules
8 molecules
1.
2.
3.
1.00 mol
2.00 mol
4.
5.
6.
4.00 mol
4.00 mol
7.
8.
9.
5.00 mol
7.00 mol
10.
11.
12.
1.00 mol
4.00 mol
13.
14.
15.
0.500 mol
0.200 mol
16.
17.
18.
32.00 g
60.02 g
19.
20.
21.
16.00 g
80.00 g
22.
23.
24.
10.00 g
20.00 g
25.
26.
27.
Section 11.4 Percent Yield
Study the diagram and the example problem.
Example Problem: The following chemical equation represents the production of gallium oxide, a substance
used in the manufacturing of some semiconductor devices.
4Ga(s) + 3O2(g) → 2Ga2O3(s)
In one experiment, the reaction yielded 7.42 g of the oxide from a 7.00-g sample of gallium. Determine the
percent yield of this reaction. The molar masses of Ga and Ga2O3 are 69.72 g/mol and 187.44 g/mol,
respectively.
Use the information in the diagram and example problem to evaluate each value or expression below. If
the value or expression is correct, write correct. If it is incorrect, write the correct value or expression.
1. actual yield: unknown ___________________________________________________________
2. mass of reactant: 7.00 g Ga ______________________________________________________
3. number of moles of reactant:
__________________________________
4. number of moles of product:
______________________________
5. theoretical yield:
6. percent yield:
__________________________________
________________________________________________
Reviewing Vocabulary
Use the following terms to complete the statements. Some terms will be used more than once.
actual yield
percent yield
stoichiometry
excess reactant
mole ratio
theoretical yield
limiting reactant
1. The reactant that limits the extent of the reaction is called the ____________________.
2. The amount of product actually produced by a chemical reaction is called the
____________________.
3. A(n) ____________________ is a ratio between the number of moles of any two substances in a
balanced chemical equation.
4. A(n) ____________________ is a reactant that has a portion remaining after the reaction has
stopped.
5. The ____________________ is the maximum amount of product that can be produced from a
given amount of reactant.
6. The study of the quantitative relationships among the amounts of reactants used and the
amounts of products formed by a chemical reaction is called ____________________.
7. The ratio of the actual yield to the theoretical yield expressed as a percent is called the
___________________.
8. The amount of product formed during a reaction depends on the ____________________.
9. A chemical reaction rarely produces the ____________________ of the product.
10. Chemists sometimes use ____________________ to speed up a chemical reaction.
Understanding Main Ideas (Part A)
Circle the letter of the choice that best completes the statement or answers the question.
1. Stoichiometry is based on the law of conservation of
a. charge.
b. mass.
c. reactants.
d. volume.
2. In a balanced chemical equation, the numbers of individual particles and the numbers of moles of
particles are represented by the
a.chemical symbols.
c. molar masses.
b. coefficients.
d. subscripts.
3. Mole ratios for a reaction are obtained from the
a. balanced chemical equation.
c. periodic table.
b. molar masses.
d. total mass of products.
4. In the decomposition reaction of compound AB into substances A and B, what is the number of mole
ratios?
a. 1
b. 3
c. 6
d. 9
5. Calculating the mass of a reactant and product from the number of moles of another product or reactant
in a chemical equation is an example of a
a. mass-to-mass conversion.
c. mole-to-mass conversion.
b. mass-to-mole conversion.
d. mole-to-mole conversion.
6. Limiting a reactant is often accomplished by
a. producing excess product.
c. slowing down a chemical reaction.
b. overcoming conservation of mass.
d. using an excess of another reactant.
7. In a reaction, substances A and B form substance C. If the actual mole ratio of substance B to
substance A is less than the balanced equation mole ratio of substance B to substance A, substance B
is the
a. actual yield.
b. excess reactant.
c. limiting reactant.
d. product.
8. Percent yield of a product is a measure of a reaction's
a. efficiency.
b. heat production.
c. rate.
d. spontaneity.
9. The actual yield of a product is
a. a negative value.
c. the same as its theoretical yield.
b. independent of the reactants.
d. measured experimentally.
10. The most important industrial chemical in the world is
a. carbon dioxide.
b. oxygen.
c. petroleum.
d. sulfuric acid.
Understanding Main Ideas (Part B)
Answer the following questions.
1. The following balanced chemical equation represents the burning of butane, a material found in some
lighters used to start fires in charcoal grills.
2C4H10(g) + 13O2(g)
8CO2(g) + 10H2O(g)
a. How many molecules of carbon dioxide are represented by the equation? _______________
b. How many moles of butane are represented by the equation? ____________________
c. Explain how you can use the balanced chemical equation to show that mass is conserved in the
reaction.
d. What is the mole ratio of butane to carbon dioxide? ____________________
e. What is the mole ratio of oxygen to butane? ____________________
2. Use the solution to the sample problem below to describe each step of the four-step procedure for
solving a mass-to-mass problem.
Example problem: The burning of 20.0 g of acetylene (C2H2) produces what mass of carbon dioxide?
Step
1
2
3
4
Explanation
Thinking Critically
Graph 1 shows the molar relationships among the reactants and products for the reaction of ammonia
and oxygen. Graph 2 shows the masses of the reactants. Use the information in the graphs to answer
the questions.
1. Write the balanced chemical equation for the reaction of ammonia and oxygen forming nitrogen oxide
and water.
2. Determine the limiting reactant.
Applying Scientific Methods
Combustion is the reaction of an element or compound with oxygen to form one or more oxides. For example,
the combustion of charcoal produces carbon dioxide.
C(s) + O2(g) → CO2(g)
As charcoal burns, or combusts, chemical energy is converted into light and heat—enough heat to cook food.
For combustion to continue, there must be material that combusts (fuel), oxygen, and heat energy. Combustion
can be controlled or stopped by limiting each or all three.
One way to extinguish a charcoal fire is to douse the coals
with water. As the liquid water reaches the hot coals, it
absorbs energy from the coals and warms. Some water
quickly changes into steam. As the water and steam continue
to gain energy, the coals lose energy and cool. The loss of
energy from the coals is sufficient to stop the combustion of
the charcoal. In effect, the water robbed the charcoal of the
energy needed to keep burning.
A less spectacular way to extinguish a charcoal fire is to
cover the burning coals. If the coals are in a grill, you can put
on the lid and close the air valves. This action makes oxygen
the limiting reactant in combustion.
Some fire extinguishers control fires by cooling the fuel and
limiting oxygen. For example, the fire extinguisher shown
produces water and carbon dioxide. To activate the fire
extinguisher, the canister must be inverted. Notice that the
canister contains a bottle of sulfuric acid immersed in a
solution of sodium carbonate. When the canister is inverted,
the stopper on the bottle falls off, and the sulfuric acid mixes
with the sodium carbonate solution. The reaction is
represented by the following chemical equation.
Na2CO3(aq) + H2SO4(aq) → Na2SO4(aq) + H2O(l) + CO2(g)
The increased pressure caused by the carbon dioxide gas in the canister propels the water from the nozzle.
The water cools the burning fuel. The carbon dioxide also does something else. Because its density is greater
than the density of oxygen, carbon dioxide displaces the oxygen around the burning fuel. The displacement
limits the oxygen available for combustion and thus aids in extinguishing the fire.
Other types of fire extinguishers cause the fuel to be the limiting reactant. They produce foams and powders
that react with the fuel. These reactions produce noncombustible products.
Liquids, foams, and powders are also used to keep potential fuels from burning. For example, timber in the
paths of forest fires can be sprayed with a variety of materials that retard fires. Some of these materials contain
ammonium phosphate and ammonium sulfate. Heat from the oncoming fire causes the ammonium compounds
to react with the cellulose in the timber and produce fire-retardant compounds. Other materials sprayed on
timber produce noncombustible foams that coat the surface of the timber. These foams retard combustion by
preventing oxygen from reacting with the timber.
1. Describe how fire-fighting techniques use the concept of limiting reactants to extinguish fires.
2. If your clothes begin to burn, safety experts advise you to "Stop, Drop, and Roll." Why?
3. Why are long, narrow plots of brush and timber often cleared in large forested areas?
4. Why is it advisable to cover a spent campfire with dirt?
5. Cellulose, a material found in plant cell walls, is the chief fuel in forest and brush fires. It is composed of
several thousand units of C12H12O10 strung end-to-end. Balance the following chemical equation for the
combustion of one C12H12O10 unit.
C12H12O10 + _______O2 → _______CO2 + _______H2O