Chapter 9
Stoichiometry
Table of Contents
Section 1 Introduction to Stoichiometry
Section 2 Ideal Stoichiometric Calculations
Section 3 Limiting Reactants and Percentage Yield
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Chapter 9
Section 1 Introduction to
Stoichiometry
Lesson Starter
Mg(s) + 2HCl(aq) ? MgCl2(aq) + H2(g)
• If 2 mol of HCl react, how many moles of H2 are obtained?
• How many moles of Mg will react with 2 mol of HCl?
• If 4 mol of HCl react, how many mol of each product are
produced?
• How would you convert from moles of substances to
mas s es?
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Chapter 9
Section 1 Introduction to
Stoichiometry
Objective
• Define stoichiometry.
• Describe the importance of the mole ratio in
s toichiometric calculations .
• Write a mole ratio relating two substances in a
chemical equation.
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Chapter 9
Section 1 Introduction to
Stoichiometry
Stoichiometry Definition
• Composition stoichiometry deals with the mass
relations hips of elements in compounds .
• Reaction stoichiometry involves the mas s
relations hips between reactants and products in a
chemical reaction.
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Chapter 9
Visual Concepts
Stoichiometry
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Visual Concept
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Chapter 9
Section 1 Introduction to
Stoichiometry
Reaction Stoichiometry Problems
Problem Type 1: Given and
unknown quantities are amounts
in moles.
Amount of given
substance (mol)
Problem Type 2: Given is an
amount in moles and unknown is
a mas s
Amount of given
substance (mol)
Amount of unknown
substance (mol)
Amount of unknown
substance (mol)
Mass of unknown
substance (g)
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Chapter 9
Section 1 Introduction to
Stoichiometry
Reaction Stoichiometry Problems, continued
Problem Type 3: Given is a
mass and unknown is an amount
in moles.
Mass of given
substance (g)
Problem Type 4: Given is a mass
and unknown is a mass.
Mass of a given substance (g)
Amount of given
substance (mol)
Amount of given
substance (mol)
Amount of unknown
substance (mol)
Mass of unknown
substance (g)
Amount of unknown
substance (mol)
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Chapter 9
Section 1 Introduction to
Stoichiometry
Mole Ratio
• A mole ratio is a conversion factor that relates the
amounts in moles of any two substances involved in a
chemical reaction
Example:
2Al2O3(l) ? 4Al(s) + 3O2(g)
Mole Ratios: 2 mol Al2O3
4 mol Al
,
2 mol Al2O3
3 mol O2
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Al
, 43mol
mol O
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Chapter 9
Section 1 Introduction to
Stoichiometry
Converting Between Amounts in Moles
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2
Chapter 9
Section 1 Introduction to
Stoichiometry
Stoichiometry
Calculations
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Chapter 9
Visual Concepts
Molar Mass as a Conversion Factor
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Visual Concept
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Lesson Starter
Acid-Base Neutralization Reaction Demonstration
• What is the equation for the reaction of HCl with
NaOH?
• W hat is the mole ratio of HCl to NaOH?
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Objective
• Calculate the amount in moles of a reactant or a
product from the amount in moles of a different
reactant or product.
• Calculate the mas s of a reactant or a product from the
amount in moles of a different reactant or product.
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Objectives, continued
• Calculate the amount in moles of a reactant or a
product from the mas s of a different reactant or
product.
• Calculate the mas s of a reactant or a product from the
mas s of a different reactant or product.
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Quantities in Moles
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Chapter 9
Visual Concepts
Conversion of Quantities in Moles
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Visual Concept
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Solving
Mass-Mass
Stoichiometry
Problems
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Quantities in Moles, continued
Sample Problem A
In a spacecraft, the carbon dioxide exhaled by astronauts
can be removed by its reaction with lithium hydroxide, LiOH,
according to the following chemical equation.
CO2(g) + 2LiOH(s) ? Li2CO3(s) + H2O(l)
How many moles of lithium hydroxide are required to react
with 20 mol CO2, the average amount exhaled by a pers on
each day?
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Quantities in Moles, continued
Sample Problem A Solution
CO2(g) + 2LiOH(s) ? Li2CO3(s) + H2O(l)
Given: amount of CO2 = 20 mol
Unknown: amount of LiOH (mol)
Solution:
mol ratio
mol CO2 ?
20 mol CO2 ?
mol LiOH
? mol LiOH
mol CO2
2 mol LiOH
? 40 mol LiOH
1 mol CO2
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Amounts in Moles to Mass
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Solving Stoichiometry
Problems with Moles or
Grams
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Amounts in Moles to Mass,
continued
Sample Problem B
In photos ynthes is , plants use energy from the sun to
produce glucos e, C6H12O6, and oxygen from the
reaction of carbon dioxide and water.
W hat mas s , in grams , of glucos e is produced when
3.00 mol of water react with carbon dioxide?
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Amounts in Moles to Mass, continued
Sample Problem B Solution
Given: amount of H2O = 3.00 mol
Unknown: mass of C6H12O6 produced (g)
Solution:
Balanced Equation: 6CO2(g) + 6H2O(l) ? C6H12O6(s) + 6O2(g)
mol ratio
mol H2O ?
3.00 mol H2O ?
molar mass factor
mol C 6H12O6
mol H2O
?
1 mol C6H12O6
?
6 mol H2O
g C 6H12O6
mol C 6H12O6
?
180.18 g C 6H12O6
1 mol C 6H12O6
g C 6H12O6
=
90.1 g C6H12O6
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Mass to Amounts in Moles
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Chapter 9
Visual Concepts
Mass and Number of Moles of an Unknown
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Visual Concept
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Mass to Amounts in Moles,
continued
Sample Problem D
The firs t s tep in the indus trial manufacture of nitric acid
is the catalytic oxidation of ammonia.
NH3(g) + O2(g) ? NO(g) + H2O(g) (unbalanced)
The reaction is run using 824 g NH3 and exces s
oxygen.
a. How many moles of NO are formed?
b. How many moles of H2O are formed?
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Conversions of Mass to Amounts in Moles, continued
Sample Problem D Solution
Given: mass of NH3 = 824 g
Unknown:
a. amount of NO produced (mol)
b. amount of H2O produced (mol)
Solution:
Balanced Equation: 4NH3(g) + 5O2(g) ? 4NO(g) + 6H2O(g)
molar mass factor
a.
g NH3 ?
mol NH3
b.
g NH3 ?
mol NH3
g NH3
g NH3
mol ratio
?
mol NO
mol NH 3
? mol NO
?
mol H2O
? mol H2O
mol NH3
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Section 2 Ideal Stoichiometric
Calculations
Chapter 9
Conversions of Mass to Amounts in Moles,
continued
Sample Problem D Solution, continued
molar mass factor
a. 824 g NH3 ?
b. 824 g NH3 ?
1 mol NH3
?
17.04 g NH3
1 mol NH3
17.04 g NH3
?
mol ratio
4 mol NO
? 48.4 mol NO
4 mol NH3
6 mol H2O
4 mol NH3
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? 72.5 mol H2O
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Mass-Mass to Calculations
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Chapter 9
Visual Concepts
Mass-Mass Calculations
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Visual Concept
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Solving Mass-Mass Problems
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Mass-Mass to Calculations, continued
Sample Problem E
Tin(II) fluoride, SnF2, is us ed in s ome toothpas tes . It is
made by the reaction of tin with hydrogen fluoride
according to the following equation.
Sn(s) + 2HF(g) ? SnF2(s) + H2(g)
How many grams of SnF2 are produced from the
reaction of 30.00 g HF with Sn?
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Mass-Mass to Calculations, continued
Sample Problem E Solution
Given: amount of HF = 30.00 g
Unknown: mas s of SnF2 produced (g)
Solution:
molar mass factor
mol ratio
molar mass factor
mol SnF2
g SnF2
mol HF
?
?
? g SnF2
g HF
mol HF
mol SnF2
1 mol SnF2
156.71 g SnF2
1 mol HF
g HF ?
?
?
20.01 g HF
2 mol HF
1 mol SnF2
g HF ?
= 117.5 g SnF2
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Solving Various Types of Stoichiometry Problems
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Solving Various Types of Stoichiometry Problems
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Solving Volume-Volume
Problems
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Chapter 9
Section 2 Ideal Stoichiometric
Calculations
Solving Particle Problems
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Chapter 9
Section 3 Limiting Reactants and
Percentage Yield
Objectives
• Describe a method for determining which of two reactants is a
limiting reactant.
• Calculate the amount in moles or mass in grams of a product,
given the amounts in moles or masses in grams of two
reactants, one of which is in excess.
• Distinguish between theoretical yield, actual yield, and
percentage yield.
• Calculate percentage yield, given the actual yield and
quantity of a reactant.
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Chapter 9
Section 3 Limiting Reactants and
Percentage Yield
Limiting Reactants
• The limiting reactant is the reactant that limits the
amount of the other reactant that can combine and the
amount of product that can form in a chemical reaction.
• The excess reactant is the substance that is not used
up completely in a reaction.
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Chapter 9
Visual Concepts
Limiting Reactants and Excess Reactants
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Visual Concept
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Chapter 9
Section 3 Limiting Reactants and
Percentage Yield
Limited Reactants, continued
Sample Problem F
Silicon dioxide (quartz) is us ually quite unreactive but
reacts readily with hydrogen fluoride according to the
following equation.
SiO2(s) + 4HF(g) ? SiF4(g) + 2H2O(l)
If 6.0 mol HF is added to 4.5 mol SiO2, which is the
limiting reactant?
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Chapter 9
Section 3 Limiting Reactants and
Percentage Yield
Limited Reactants, continued
Sample Problem F Solution
SiO2(s) + 4HF(g) ? SiF4(g) + 2H2O(l)
Given: amount of HF = 6.0 mol
amount of SiO2 = 4.5 mol
Unknown: limiting reactant
mole ratio
Solution:
mol HF ?
mol SiO2 ?
mol SiF4
mol HF
? mol SiF4 produced
mol SiF4
? mol SiF4 produced
mol SiO2
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Chapter 9
Section 3 Limiting Reactants and
Percentage Yield
Limited Reactants, continued
Sample Problem F Solution, continued
SiO2(s) + 4HF(g) ? SiF4(g) + 2H2O(l)
6.0 mol HF ?
1 mol SiF4
? 1.5 mol SiF4 produced
4 mol HF
4.5 mol SiO2 ?
1 mol SiF4
? 4.5 mol SiF4 produced
1 mol SiO2
HF is the limiting reactant.
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Chapter 9
Section 3 Limiting Reactants and
Percentage Yield
Percentage Yield
• The theoretical yield is the maximum amount of
product that can be produced from a given amount of
reactant.
• The actual yield of a product is the meas ured amount
of that product obtained from a reaction.
• The percentage yield is the ratio of the actual yield to
the theoretical yield, multiplied by 100.
percentage yield ?
actual yield
? 100
theorectical yield
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Chapter 9
Visual Concepts
Comparing Actual and Theoretical Yield
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Visual Concept
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Section 3 Limiting Reactants and
Percentage Yield
Chapter 9
Percentage Yield, continued
Sample Problem H
Chlorobenzene, C6H5Cl, is us ed in the production of
many important chemicals , s uch as as pirin, dyes , and
dis infectants . One indus trial method of preparing
chlorobenzene is to react benzene, C6H6, with chlorine,
as represented by the following equation.
C6H6 (l) + Cl2(g) ? C6H5Cl(l) + HCl(g)
When 36.8 g C6H6 react with an exces s of Cl2, the
actual yield of C6H5Cl is 38.8 g.
W hat is the percentage yield of C6H5Cl?
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Section 3 Limiting Reactants and
Percentage Yield
Chapter 9
Percentage Yield, continued
Sample Problem H Solution
C6H6 (l) + Cl2(g) ? C6H5Cl(l) + HCl(g)
mass of C6H6 = 36.8 g
mass of Cl2 = excess
actual yield of C6H5Cl = 38.8 g
Unknown: percentage yield of C6H5Cl
Solution:
Theoretical yield
Given:
molar mass factor
g C 6H6 ?
mol C 6H6
g C 6H6
mol ratio
molar mass
mol C 6H5Cl
?
mol C 6H6
?
g C 6H5Cl
? g C 6H5Cl
mol C 6H5Cl
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Chapter 9
Section 3 Limiting Reactants and
Percentage Yield
Percentage Yield, continued
Sample Problem H Solution, continued
C6H6(l) + Cl2(g) ?
C6H5 Cl(l) + HCl(g)
Theoretical yield
36.8 g C 6H6 ?
1 mol C 6H6
78.12 g C 6H6
?
1 mol C 6H5Cl
1 mol C 6H6
?
112.56 g C 6H5Cl
1 mol C 6H5Cl
? 53.0 g C 6H5Cl
Percentage yield
percentage yield C 6H5Cl ?
percentage yield ?
actual yield
? 100
theorectical yield
38.8 g
? 100 ? 73.2%
53.0 g
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End of Chapter 9 Show
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Chapter 9
Standardized Test Preparation
Multiple Choice
1. In s toichiometry, chemis ts are mainly concerned with
A.
B.
C.
D.
the types of bonds found in compounds .
mass relations hips in chemical reactions .
energy changes occurring in chemical reactions .
the s peed with which chemical reactions occur.
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Chapter 9
Standardized Test Preparation
Multiple Choice
1. In s toichiometry, chemis ts are mainly concerned with
A.
B.
C.
D.
the types of bonds found in compounds .
mass relations hips in chemical reactions .
energy changes occurring in chemical reactions .
the s peed with which chemical reactions occur.
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Chapter 9
Standardized Test Preparation
Multiple Choice
2. As s ume ideal s toichiometry in the reaction
CH4 + 2O2 ? CO2 + 2H2O. If you know the mass of
CH4, you can calculate
A.
B.
C.
D.
only the mas s of CO2 produced.
only the mas s of O2 reacting.
only the mas s of CO2 + H2O produced.
the mas s of O2 reacting and CO2 + H2O produced.
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Chapter 9
Standardized Test Preparation
Multiple Choice
2. As s ume ideal s toichiometry in the reaction
CH4 + 2O2 ? CO2 + 2H2O. If you know the mass of
CH4, you can calculate
A.
B.
C.
D.
only the mas s of CO2 produced.
only the mas s of O2 reacting.
only the mas s of CO2 + H2O produced.
the mas s of O2 reacting and CO2 + H2O produced.
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Chapter 9
Standardized Test Preparation
Multiple Choice
3. Which mole ratio for the equation 6Li + N2 ? 2Li3N is
incorrect?
A. 6 mol Li
2 mol N2
B.
1 mol N2
6 mol Li
C. 2 mol Li3N
1 mol N2
D.
2 mol Li3N
6 mol Li
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Chapter 9
Standardized Test Preparation
Multiple Choice
3. Which mole ratio for the equation 6Li + N2 ? 2Li3N is
incorrect?
A. 6 mol Li
2 mol N2
B.
1 mol N2
6 mol Li
C. 2 mol Li3N
1 mol N2
D.
2 mol Li3N
6 mol Li
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Chapter 9
Standardized Test Preparation
Multiple Choice
4. For the reaction below, how many moles of N2 are
required to produce 18 mol NH3?
N2 + 3H2 ? 2NH3
A. 4.5
B. 9.0
C. 18
D. 36
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Chapter 9
Standardized Test Preparation
Multiple Choice
4. For the reaction below, how many moles of N2 are
required to produce 18 mol NH3?
N2 + 3H2 ? 2NH3
A. 4.5
B. 9.0
C. 18
D. 36
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Chapter 9
Standardized Test Preparation
Multiple Choice
5. What mas s of NaCl can be produced by the reaction of
0.75 mol Cl2?
2Na + Cl2 ? 2NaCl
A. 0.75 g
B. 1.5 g
C. 44 g
D. 88 g
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Chapter 9
Standardized Test Preparation
Multiple Choice
5. What mas s of NaCl can be produced by the reaction of
0.75 mol Cl2?
2Na + Cl2 ? 2NaCl
A. 0.75 g
B. 1.5 g
C. 44 g
D. 88 g
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Chapter 9
Standardized Test Preparation
Multiple Choice
6. W hat mas s of CO2 can be produced from 25.0 g
CaCO3 given the decompos ition reaction
CaCO3 ? CaO + CO2
A. 11.0 g
B. 22.0 g
C. 25.0 g
D. 56.0 g
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Chapter 9
Standardized Test Preparation
Multiple Choice
6. W hat mas s of CO2 can be produced from 25.0 g
CaCO3 given the decompos ition reaction
CaCO3 ? CaO + CO2
A. 11.0 g
B. 22.0 g
C. 25.0 g
D. 56.0 g
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Chapter 9
Standardized Test Preparation
Multiple Choice
7. If a chemical reaction involving substances A and B
s tops when B is completely used up, then B is referred
to as the
A. excess reactant.
B. primary reactant.
C. limiting reactant.
D. primary product.
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Chapter 9
Standardized Test Preparation
Multiple Choice
7. If a chemical reaction involving substances A and B
s tops when B is completely used up, then B is referred
to as the
A. excess reactant.
B. primary reactant.
C. limiting reactant.
D. primary product.
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Chapter 9
Standardized Test Preparation
Multiple Choice
8. If a chemis t calculates the maximum amount of product
that could be obtained in a chemical reaction, he or
s he is calculating the
A. percentage yield.
B. mole ratio.
C. theoretical yield.
D. actual yield.
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Chapter 9
Standardized Test Preparation
Multiple Choice
8. If a chemis t calculates the maximum amount of product
that could be obtained in a chemical reaction, he or
s he is calculating the
A. percentage yield.
B. mole ratio.
C. theoretical yield.
D. actual yield.
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Chapter 9
Standardized Test Preparation
Multiple Choice
9. W hat is the maximum number of moles of AlCl3 that
can be produced from 5.0 mol Al and 6.0 mol Cl2?
2Al + 3Cl2 ? 2AlCl3
A. 2.0 mol AlCl3
B. 4.0 mol AlCl3
C. 5.0 mol AlCl3
D. 6.0 mol AlCl3
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Chapter 9
Standardized Test Preparation
Multiple Choice
9. W hat is the maximum number of moles of AlCl3 that
can be produced from 5.0 mol Al and 6.0 mol Cl2?
2Al + 3Cl2 ? 2AlCl3
A. 2.0 mol AlCl3
B. 4.0 mol AlCl3
C. 5.0 mol AlCl3
D. 6.0 mol AlCl3
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Chapter 9
Standardized Test Preparation
Short Answer
10. W hy is a balanced equation neces s ary to solve a
mas s -mas s s toichiometry problem?
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Chapter 9
Standardized Test Preparation
Short Answer
10. W hy is a balanced equation neces s ary to solve a
mas s -mas s s toichiometry problem?
Answer: The coefficients of the balanced equation are
needed for the mole-mole ratio that is neces s ary to
s olve s toichiometric problems involving two different
s ubs tances .
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Chapter 9
Standardized Test Preparation
Short Answer
11. What data are neces s ary to calculate the percentage
yield of a reaction?
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Chapter 9
Standardized Test Preparation
Short Answer
11. W hat data are neces s ary to calculate the percentage
yield of a reaction?
Answer: the theoretical yield and the actual yield of the
product
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Chapter 9
Standardized Test Preparation
Extended Response
12. A student makes a compound in the laboratory and
reports an actual yield of 120%. Is this result possible?
Assuming that all masses were measured correctly, give
an explanation.
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Chapter 9
Standardized Test Preparation
Extended Response
12. A student makes a compound in the laboratory and
reports an actual yield of 120%. Is this result possible?
Assuming that all masses were measured correctly, give
an explanation.
Answer: The product was impure, so the mass contained
the product and other substances. For example, if NaCl
is made from HCl and NaOH but is not dried, the mass
of NaCl can include water, which would result in a yield
greater than 100%.
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Chapter 9
Standardized Test Preparation
Extended Response
13. Benzene, C6H6, is reacted with bromine, Br2, to
produce bromobenzene, C6H5Br, and hydrogen
bromide, HBr, as shown below. W hen 40.0 g of
benzene are reacted with 95.0 g of bromine, 65.0 g of
bromobenzene is produced.
C6H6 + Br2 ? C6H5Br + HBr
a. W hich compound is the limiting reactant?
b. W hat is the theoretical yield of bromobenzene?
c. W hat is the reactant in exces s , and how much remains
after the reaction is completed?
d. W hat is the percentage yield?
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 9
Standardized Test Preparation
Extended Response
13. Benzene, C6H6, is reacted with bromine, Br2, to
produce bromobenzene, C6H5Br, and hydrogen
bromide, HBr, as shown below. W hen 40.0 g of
benzene are reacted with 95.0 g of bromine, 65.0 g of
bromobenzene is produced.
C6H6 + Br2 ? C6H5Br + HBr
a. W hich compound is the limiting reactant? benzene
b. W hat is the theoretical yield of bromobenzene? 80.4 g
c. W hat is the reactant in exces s , and how much remains
after the reaction is completed? bromine, 13.2 g
d. W hat is the percentage yield? 80.8%
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.