05 ctr ch20 7/12/04 8:17 am page 517 the meaning of...

Chapter 20 Oxidation-Reduction Reactions 517

Section Review

Objectives• Define oxidation and reduction in terms of the loss or gain of oxygen or hydrogen

and the loss or gain of electrons

• State the characteristics of a redox reaction and identify the oxidizing agent andreducing agent

Vocabulary

Part A CompletionUse this completion exercise to check your understanding of the concepts and termsthat are introduced in this section. Each blank can be completed with a term, shortphrase, or number.

Oxidation–reduction, or , reactions are an important 1.

category of chemical reactions. Oxidation is considered to be any 2.

shift of electrons from an atom. Reduction includes any 3.

shift of electrons an atom. An oxidation reaction is always 4.

accompanied by a reaction. The substance that does the 5.

oxidizing (the agent) is . The substance that does 6.

the reducing (the agent) is . 7.

8.

Part B True-FalseClassify each of these statements as always true, AT; sometimes true, ST; or never true, NT.

________ 9. Reduction is the complete or partial gain of electrons by a substance.

________ 10. In the reaction 2Na � Cl2y 2NaCl, sodium is the reducing agent.

________ 11. In the reaction 2Na � Cl2y 2NaCl, sodium is being reduced.

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• oxidation-reduction reactions

• redox reactions

• oxidation

• reduction

• reducing agent

• oxidizing agent

Name ___________________________ Date ___________________ Class __________________

THE MEANING OF OXIDATION AND REDUCTION

20.1

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518 Core Teaching Resources

________ 12. To protect an iron ship hull, you should attach a metal that is easilyreduced.

Part C MatchingMatch each description in Column B to the correct term in Column A.

Part D Questions and ProblemsAnswer the following in the space provided.

19. Define oxidation and reduction in terms of the loss or gain of electrons.

20. In the equation given, identify the substance oxidized, the substance reduced,the oxidizing agent, and the reducing agent.

Zn � Cu2�y Zn2� � Cu

21. Explain how putting a block of zinc or aluminum on the iron hull of a large shipwill protect the ship from corrosion.

Column B

a. a metal that loses electrons easily

b. complete or partial loss of electrons or gain of oxygen

c. oxidation of metals to metallic ions by oxygen andwater in the environment

d. a metal that resists corrosion

e. a chemical change in which oxygen reacts withanother substance, often producing energy in theform of heat and light

f. a substance that accepts electrons in a redox reaction

Column A

________ 13. combustion

________ 14. oxidation

________ 15. oxidizing agent

________ 16. corrosion

________ 17. zinc

________ 18. gold

Name ___________________________ Date ___________________ Class __________________©

Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.

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Section Review

Objectives• Determine the oxidation number of an atom of any element in a pure substance

• Define oxidation and reduction in terms of a change in oxidation number, andidentify atoms being oxidized or reduced in redox reactions

Vocabulary• oxidation number

Part A CompletionUse this completion exercise to check your understanding of the concepts and termsthat are introduced in this section. Each blank can be completed with a term, shortphrase, or number.

The oxidation number of an element in an uncombined state 1.

is . The oxidation number of a monatomic ion is the same 2.

in magnitude and as its ionic . The sum of the 3.

oxidation numbers of the elements in a neutral compound is 4.

. In a polyatomic ion, however, the sum is equal to the 5.

. Oxidation numbers help you keep track of – 6.

transfer in redox reactions. An oxidation number increase is 7.

, while a is reduction. 8.


________ 9. Oxygen is more electronegative than chlorine.

________ 10. The oxidation number of each oxygen atom in most compounds is �2.

________ 11. The oxidation number of Cl in KClO3 is �1.

________ 12. The oxidation number of each hydrogen atom in most compounds is �1.

________ 13. The oxidation number for copper in a copper penny is �2.

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OXIDATION NUMBERS20.2

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________ 14. In the reaction C � H2O y CO � H2, the oxidation number of thehydrogen doesn’t change.

________ 15. In the reaction C � H2O y CO � H2, the oxidation number of thecarbon increases.

________ 16. An increase in the oxidation number of an atom indicates oxidation.

Part C MatchingMatch the oxidation number of nitrogen in each formula in Column B to the correctoxidation number in Column A.


26. Define oxidation and reduction in terms of a change in oxidation number.

27. Use the change in oxidation number to determine which elements are oxidizedand which are reduced in these reactions. (Note: It is not necessary to usebalanced equations.)

a. HNO3 � HBr y NO � Br2 � H2O

b. KMnO4 � HCl yMnCl2 � Cl2 � H2O � KCl

c. Sb � HNO3y Sb2O5 � NO � H2O

d. C � H2SO4y CO2 � SO2 � H2O

Column B

a. N2

b. HNO3

c. NO

d. NH2OH

e. NH3

f. N2O3

g. N2O

h. N2H4

i. NO2

Column A

________ 17. �3

________ 18. �2

________ 19. �1

________ 20. 0

________ 21. �1

________ 22. �2

________ 23. �3

________ 24. �4

________ 25. �5

Name ___________________________ Date ___________________ Class __________________©


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Section Review

Objectives• Balance a redox equation using the oxidation-number-change method

• Balance a redox equation by breaking a redox equation into oxidation andreduction half-reactions and then using the half-reaction method

Vocabulary• oxidation-number-change method

• half-reaction

• half-reaction method

Part A CompletionUse this completion exercise to check your understanding of the concepts and termsthat are introduced is this section. Each blank can be completed with a term, shortphrase, or number.

One method for balancing redox equations involves 1.

determining the change in of the substances that are 2.

oxidized and reduced. Coefficients are then used to make the 3.

increase in oxidation number equal to the decrease. 4.

The method is another way to write a 5.

equation for a redox reaction. In this method, the net 6.

equation is divided into half-reactions. Each half-reaction 7.

is balanced independently. Finally, the half-reactions are .

The half-reaction method is particularly useful in balancing

equations for reactions.


________ 8. The reduction half-reaction in the reaction MnO4�� Cl�yMn2� �

Cl2 involves MnO4�yMn2�

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BALANCING REDOX REACTIONS20.3

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05_CTR_ch20 7/12/04 8:17 AM 21


________ 9. In an oxidation half-reaction, electrons occur on the right side of theequation.

________ 10. Electrons never appear in a balanced redox reaction.

________ 11. 2e� � 2Cl�y Cl2 is a balanced half-reaction.

________ 12. To balance the oxygen in a half reaction involving MnO4�yMn2�,

2H2O will be added to the product side of the equation.

________ 13. In the equation 2FeBr2 � Br2y 2FeBr3, the oxidation number of theiron doesn’t change.

Part C MatchingMatch each description in Column B to the correct term in Column A.


21. Balance these redox equations using the oxidation-number-change method.

a. HNO3(aq) � HI(g) y NO(g) � I2(s) � H2O

b. HNO3(aq) � I2(s) y HIO3(aq) � NO2(g) � H2O(l)

22. Balance these redox equations using the half-reaction method.

a. H2S(aq) � HNO3(aq) y S(s) � NO(g) � H2O(l)

b. Fe2� � Cr2O72�y Fe3� � Cr3�

Column B

a. ions that are present but do not participate in orchange during the reaction

b. Fe2�y Fe3� � e�

c. balancing a redox equation by first balancing theoxidation and reduction half-reactions

d. balancing a redox equation by comparing the increaseand decrease in oxidation numbers

e. equation showing either the reduction or the oxidationof a species in an oxidation-reduction reaction

f. ions that can serve as reducing agents

g. 2e� � Br2y 2Br�

Column A

________ 14. half-reaction method

________ 15. spectator ions

________ 16. anions

________ 17. oxidation half-reaction

________ 18. half-reaction

________ 19. oxidation-number-change method

________ 20. reduction half-reaction

Name ___________________________ Date ___________________ Class __________________©


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Practice ProblemsIn your notebook, solve the following problems.

SECTION 20.1 THE MEANING OF OXIDATION AND REDUCTIONDetermine what is oxidized and what is reduced in each reaction. Identify theoxidizing agent and the reducing agent.

1. 2Sr � O2y 2SrO

2. 2Li � S y 2Li2S

3. 2Cs � Br2y 2CsBr

4. 3Mg � N2yMg3N2

5. 4Fe � 3O2y 2Fe2O3

6. Cl2 � 2NaBr y 2NaCl � Br2

7. Si � 2F2y SiF4

8. 2Ca � O2y 2CaO

9. Mg � 2HCl yMgCl2 � H2

10. 2Na � 2H2O y 2NaOH � H2

SECTION 20.2 OXIDATION NUMBERS1. Give the oxidation number of each kind of atom or ion.

a. Sn c. S2� e. Se g. Sn4�

b. K� d. Fe3� f. Mg2� h. Br�

2. Calculate the oxidation number of chromium in each of the following formulas.

a. Cr2O3 b. H2Cr2O7 c. CrSO4 d. CrO42�

3. Use the changes in oxidation number to determine which elements are oxidizedand which are reduced in these reactions. (Note: It is not necessary to usebalanced reactions.)

a. C � H2SO4y CO2 � SO2 � H2O

b. HNO3 � HI y NO � I2 � H2O

c. KMnO4 � HCl yMnCl2 � Cl2 � H2O � KCl

d. Sb � HNO3y Sb2O5 � NO � H2O

4. For each reaction in problem 3 above, identify the oxidizing agent and reducingagent.

Name ___________________________ Date ___________________ Class __________________

OXIDATION-REDUCTION REACTIONS20

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SECTION 20.3 BALANCING REDOX EQUATIONS1. Balance these equations using the oxidation-number-change method.

a. C � H2SO4y CO2 � SO2 � H2O

b. H2S � HNO3y S � NO � H2O

c. HNO3 � HI y NO � I2 � H2O

d. Sb � HNO3y Sb2O5 � NO � H2O

e. KMnO4 � HCl yMnCl2 � Cl2 � H2O � KCl

f. KIO4 � KI � HCl y KCl � I2 � H2O

g. Zn � Cr2O72� � H�y Zn2� � Cr3� � H2O

2. Write half-reactions for the oxidation and reduction processes for each of thefollowing reactions.

a. Fe2� � MnO4�y Fe3� � Mn2� (acidic solution)

b. Sn2� � IO3�y Sn4� � I� (acidic solution)

c. S2� � NO3�y S � NO (acidic solution)

d. Mn2� � H2O2yMnO2 � H2O (basic solution)

3. Balance these reactions using the half-reaction method.

a. Zn � HgO y ZnO22� � Hg (basic solution)

b. Fe2� � MnO4�y Fe3� � Mn2� (acidic solution)

c. Sn2� � IO3�y Sn4� � I� (acidic solution)

d. S2� � NO3�y S � NO (acidic solution)

e. Mn2� � H2O2yMnO2 � H2O (basic solution)

f. CrO2 � ClO�y CrO42� � Cl� (basic solution)

Name ___________________________ Date ___________________ Class __________________©


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Figure 1 Titration of iron(II) ion (Fe2�) with a standard solution of 0.0200M potassium permanganate (KMnO4).

To determine the relative amount of iron in a sample of iron ore, a chemist dissolved2.938 g of the ore in 50.0 mL of dilute sulfuric acid (H2SO4) in a reaction flask. Thecolorless solution was then titrated to the end point with potassium permanganate.The half-reactions for the oxidation and reduction processes that occur during thistitration are:

Fe2�y Fe3�

MnO4�yMn2�

Use the data in Table 1 and what you have learned about oxidation-reductionreactions to answer the following questions.

Clamp

Ring stand

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INTERPRETING GRAPHICSUse with Section 20.3

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Table 1 Analysis of an Unknown Iron-Containing Ore

1. Match each component from the following list with the correct number shownin Figure 1. The same number may be used more than once.

________ a. oxidizing agent

________ b. reducing agent

________ c. standard solution of 0.0200M KMnO4

________ d. acidic solution of iron(II) ion, Fe2�

________ e. reaction flask

________ f. buret

2. Use the half-reaction method to balance the equation for the redox reactionbetween permanganate ion and iron(II) ion. Write the net ionic equation only.

3. Explain what the end point of this particular titration means in terms of thereacting species in solution. How does the chemist recognize the end pointwhen it occurs?

4. Use the stoichiometry of the balanced equation given in your answer toquestion 2 and the fact that the molar mass of Fe is 55.85 g to complete Table 1above. Use the space below to show your work.

Name ___________________________ Date ___________________ Class __________________©


Initial Volume of KMnO4 48.65 mL

Final Volume of KMnO4 23.35 mL

Volume of MnO4�

Moles MnO4�

Moles Iron(II), Fe2�

Mass of Iron

% of Iron in Ore

05_CTR_ch20 7/12/04 8:17 AM Page 526


Name ___________________________ Date ___________________ Class __________________

half-reaction oxidation-reduction reaction

half-reaction method oxidizing agent

oxidation redox reaction

oxidation number reducing agent

oxidation-number-change method reduction

1. the substance in a redox reaction that accepts electrons

2. a method of balancing a redox equation by comparing the increases anddecreases in oxidation numbers

3. a process that involves a complete or partial gain of electrons or the loss ofoxygen; it results in a decrease in the oxidation number of an atom

4. a method for balancing a redox equation by balancing the oxidation andreduction half-reactions

5. a positive or negative number assigned to a combined atom according to aset of arbitrary rules

6. a substance in a redox reaction that donates electrons

7. an equation showing either the reduction or the oxidation of a species in anoxidation-reduction reaction

8. a reaction that involves the transfer of electrons between reactants during achemical change

9. a process that involves complete or partial loss of electrons or a gain ofoxygen; it results in an increase in the oxidation number of an atom

10. another name for an oxidation-reduction reaction

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Vocabulary ReviewSelect the term from the following list that best matches each description.

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Chapter QuizChoose the best answer and write its letter on the line.

________ 1. The oxidation number of sulfur in each of the following is �6 except for 20.2a. SO3. c. SO4

2�.b. S2O3

2�. d. Na2SO4.

________ 2. Reduction is 20.1a. a gain of electrons. c. a gain of oxygen.b. a loss of electrons. d. both a and c

________ 3. Identify the oxidizing agent in the following reaction. 20.1

2Na � S y Na2S

a. Na c. Na2Sb. S d. Na�

________ 4. From the unbalanced equations below, identify the one that does 20.1not represent a redox reaction.a. HNO3(aq) � H3PO3(aq) y NO(g) � H3PO4(aq) � H2O(l)b. H2SO4(aq) � NaOH(aq) y H2O(l) � Na2SO4(aq)c. C(s) � O2(g) y CO2(g)d. H2O2(aq) � PbS(s) y PbSO4(s) � H2O(l)

________ 5. Identify the oxidation half-reaction among the following. 20.3a. Fe2�y Fe3� � e� c. O2 � 4H� � 4e�y 2H2Ob. Cl2 � 2e�y 2Cl� d. Fe3� � e�y Fe2�

________ 6. What will the coefficient of HNO3 be when the following equation is 20.3completely balanced using the smallest whole-number coefficients?

HNO3 � MnCl2 � HCl y NO � MnCl4 � H2O

a. 2 c. 6b. 3 d. 5

________ 7. When the half-reactions I2 � 2e�y 2I� and Na y Na� � e� are 20.3correctly combined, the balanced redox equation isa. Na � I � e�y Na� � 2I�

b. Na � I2y Na� � 2I�

c. 2Na � I2y 2Na� � 2I�

d. Na � I2 � 2e�y Na� � 2I� � e�

________ 8. What is the reduction half-reaction for the following unbalanced redox 20.3equation?

Cr2O72� � NH4

�y Cr2O3 � N2

a. NH4�y N2 c. Cr2O3y Cr2O7

2�

b. N2y NH4� d. Cr2O7

2�y Cr2O3

Name ___________________________ Date ___________________ Class __________________©



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Chapter Test A

A. MatchingMatch each term in Column B with the correct description in Column A.

B. Multiple ChoiceChoose the best answer and write its letter on the line.

________ 11. Identify the oxidizing agent in the following reaction.

2Na � 2H2O y 2NaOH � H2

a. Na c. NaOHb. H2O d. H2

________ 12. Identify the reducing agent in the following reaction.

CH4 � 2O2y CO2 � 2H2O

a. H2O b. O2

b. CO2 d. CH4

Column B

a. half-reaction

b. oxidation-number-change method

c. oxidation

d. oxidation number

e. half-reaction method

f. oxidation-reductionreaction

g. spectator ion

h. reducing agent

i. reduction

j. oxidizing agent

Column A

________ 1. a positive or negative number assigned to an atomaccording to a set of arbitrary rules

________ 2. the substance in a redox reaction that acceptselectrons

________ 3. chemical change that occurs when electrons aretransferred between reactants

________ 4. an equation showing either the reduction or theoxidation of a species in a redox reaction

________ 5. complete or partial gain of electrons or loss of oxygen

________ 6. ion that does not change oxidation number orcomposition during a reaction

________ 7. balances redox reactions by balancing oxidation andreduction half-reactions

________ 8. balances a redox reaction by comparing the increasesand decreases in oxidation numbers

________ 9. complete or partial loss of electrons or gain of oxygen

________ 10. the substance in a redox reaction that donateselectrons

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________ 13. Nitrogen has the same oxidation number in all of the following excepta. NO3

�. c. NH4Cl.b. N2O5. d. Ca(NO3)2.

________ 14. Determine what happens in this reaction.

S � Cl2y SCl2

(Hint: Chlorine is the more electronegative element.)a. Sulfur is reduced.b. Chlorine is reduced.c. Chlorine is oxidized.d. Sulfur is the oxidizing agent.

________ 15. Zn y Zn2� representsa. oxidation. c. both a and bb. reduction. d. neither a nor b

________ 16. Sn4�y Sn2� representsa. oxidation. c. hydrolysis.b. reduction. d. none of the above

________ 17. What happens to chlorine (in ClO3�) in the following redox reaction?

ClO3� � I�y Cl� � I2

a. It is oxidized.b. Its oxidation number changes from �6 to �1.c. Its oxidation-number change is �6.d. Its oxidation-number change is �6.

________ 18. Identify the atom that increases in oxidation number in the followingredox reaction.

2MnO2 � 2K2CO3 � O2y 2KMnO4 � 2CO2

a. C c. Mnb. K d. O

________ 19. Identify the reducing agent in this reaction.

I� � MnO4�y I2 � MnO2

a. I� c. I2

b. MnO4� d. MnO2

________ 20. What is the increase in oxidation number for the atom that is oxidizedin the following balanced redox equation?

Cr2O72� � 8H� � 3SO3

2�y Cr3� � 3SO42� � 8H2O

a. �2 c. �3b. �6 d. �6

________ 21. To balance the oxygen and hydrogen for a redox reaction that takesplace in basic solution, it is necessary to usea. H2O and H�. c. H2O and OH�.b. H2O only. d. OH� only.

________ 22. Which of the following is an oxidation half-reaction?a. Zn2� � 2e�y Zn c. Na� � e�y Nab. NO � 2H2O y NO3

� � 4H� � 3e� d. 2H� � 2e�y H2

Name ___________________________ Date ___________________ Class __________________©


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________ 23. What is the reduction half-reaction for the following unbalanced redoxequation?

Cr2O72� � Fe2�y Cr3� � Fe3�

a. Cr3�y Cr2O72� c. Fe3�y Fe2�

b. Fe2�y Fe3� d. Cr2O72�y Cr3�

________ 24. Which atom is reduced in the following unbalanced redox equations?

K2Cr2O7 � H2O � S y KOH � Cr2O3 � SO2

a. S c. Crb. O d. K

________ 25. Identify a true statement about how to protect an iron object fromcorrosion.a. Increase the amount of salt and/or acid in the water.b. Place a gold or silver bar in contact with the iron.c. Place a better reducing agent in contact with the iron.d. Place a metal more easily reduced in contact with the iron.

________ 26. Identify from the unbalanced equations below the one that does notrepresent a redox reaction.a. H2O2(aq) � MnO4

�(aq) y O2(g) � Mn2�(aq)b. H2(g) � N2(g) y NH3(g)c. NaCl(aq) � AgNO3(aq) y NaNO3(aq) � AgCl(s)d. Cu(s) � AgNO3(aq) y Cu(NO3)2(aq) � Ag(s)

C. QuestionsAnswer the following questions in the space provided.

27. Determine which substance is oxidized and which substance is reduced in eachreaction. Identify the oxidizing agent and reducing agent in each case.

a. 2Na � Br2y 2NaBr

b. 2K � S y K2S

28. Combine these two half-reactions to form a balanced redox equation.

Br2 � 2e�y 2Br� and Cr y Cr3� � 3e�

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29. Determine the oxidation number of each element in these substances.a. Li3AlF6

b. Na2O

c. S8

30. Balance the following redox equation, using either the oxidation-number-change method or the half-reaction method. Show all your work. (In using thehalf-reaction method, assume that the reaction occurs in aqueous acidsolution.)

Fe2O3 � CO y Fe � CO2 (acid solution)

D. Essay31. How are oxidation numbers determined and used?

Name ___________________________ Date ___________________ Class __________________©


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Chapter Test B

A. MatchingMatch each term in Column B with the correct description in Column A. Write theletter of the correct term on the line.

B. Multiple ChoiceChoose the best answer and write its letter on the line.

________ 11. Which of the following is true about oxidation reactions?a. Oxidation reactions are the principal source of energy on Earth.b. All oxidation reactions are accompanied by reduction reactions.c. The burning of wood in a fireplace and the metabolization of

food by your body are oxidation reactions.d. all of the above

Column B

a. oxidation-number-change method

b. reducing agent

c. oxidation-reductionreactions

d. spectator ions

e. oxidizing agent

f. reduction

g. oxidation number

h. half-reaction method

i. oxidation

j. redox reaction

Column A

________ 1. the substance in a redox reaction that acceptselectrons

________ 2. the complete or partial gain of electrons or the loss ofoxygen

________ 3. those ions that do not change oxidation number orcomposition during a reaction

________ 4. a positive or negative number assigned to an atomaccording to a set of arbitrary rules

________ 5. the complete or partial loss of electrons or the gain ofoxygen

________ 6. the balancing of a redox reaction by comparing theincreases and decreases in oxidation numbers

________ 7. the chemical changes that occur when electrons aretransferred between reactants

________ 8. a method of balancing redox reactions by balancingthe oxidation and reduction half-reactions

________ 9. the substance in a redox reaction that donateselectrons

________ 10. another name for an oxidation-reduction reaction

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________ 12. What is the oxidized substance in the following reaction?

Fe � 2HCl y FeCl2 � H2

a. Fe c. FeCl2

b. HCl d. H2

________ 13. The reducing agent in the reaction described in question 12 isa. Fe. c. FeCl2.b. HCl. d. H2.

________ 14. What is occurring in the following reaction?

H2 � Cl2y 2HCl

a. H2 is being reduced.b. Cl2 is being oxidized.c. H2 is gaining two electrons.d. Cl2 is acting as an oxidizing agent.

________ 15. What is the oxidation number of sulfur in H2SO3?a. �1 c. �3b. �2 d. �4

________ 16. What is the usual oxidation number of oxygen in a compound?a. �1 c. �1b. �2 d. �2

________ 17. In the unbalanced equation below, what element is being reduced?

MnO2 � HCl y H2O � MnCl2 � Cl2

a. Mn c. Hb. O d. Cl

________ 18. Which of the following is an oxidation reaction?

a. Co3�y Co2� c. AuCl4�y AuCl2

�

b. Cl2y ClO3� d. Mn7�yMn2�

________ 19. Among the following, which is an oxidation-reduction reaction?a. Na2S � CaCO3y CaS � Na2CO3

b. 2HNO3 � Mg(OH)2yMg(NO3)2 � 2H2Oc. H2 � F2y 2HFd. 3Ba(OH)2 � 2H3PO4y Ba3(PO4)2 � 6H2O

________ 20. Which of the following is true concerning the reaction below?

H2S � HNO3y S � NO � H2O

a. S is reduced. c. N is reduced.b. H is oxidized. d. O is oxidized.

________ 21. When the equation in question 20 is balanced, what is the coefficientfor H2O?a. 2 c. 3b. 4 d. 6

Name ___________________________ Date ___________________ Class __________________©


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________ 22. In the equation PbO2 � 4HCl y 2H2O � PbCl2 � Cl2, how manyelectrons are transferred?a. 1 c. 3b. 2 d. 4

________ 23. The element oxidized in the reaction described in question 22 isa. Pb. c. H.b. O. d. Cl.

________ 24. In the unbalanced equation given below, what is the element that isgaining electrons?

HCl � MnO2yMnCl2 � H2O � Cl2

a. H c. Mnb. Cl d. O

________ 25. When the equation in question 24 is balanced, what is the coefficientfor HCl?a. 1 c. 3b. 2 d. 4

________ 26. Which of the following is true concerning redox reactions?a. Double-replacement reactions are always redox reactions.b. Single-replacement reactions may be redox reactions.c. Acid-base reactions are always redox reactions.d. all of the above

________ 27. Identify a false statement about how to protect iron from corrosion.a. Coat the surface with oil, paint, or plastic.b. Attach a metal that is more easily reduced.c. Exclude air and water.d. Attach a metal that is a better reducing agent.

________ 28. From the unbalanced equations below, identify the one that does notrepresent a redox reaction.a. H2CO3(aq) y CO2(g) � H2O(l)b. C(s) � H2O(g) y CO(g) � H2(g)c. S2O3

2�(aq) � I2(s) y S4O62�(aq) � I�(aq)

d. FeBr2(aq) � Br2(l) y FeBr3(aq)

Name ___________________________ Date ___________________ Class __________________©

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C. QuestionsAnswer the following questions in the space provided.

29. For each of the following reactions, identify the element oxidized, the elementreduced, the oxidizing agent, and the reducing agent.

30. Determine the oxidation number of each element in the following.

a. K2SO4

b. Cu(NO3)2

c. HAsO3

d. MnO4�

31. Use the oxidation-number-change method to balance the equations givenbelow. Show all your work.

a. HNO3 � Ag y AgNO3 � NO � H2O

b. Br2 � SO2 � H2O y H2SO4 � HBr

Name ___________________________ Date ___________________ Class __________________©


Oxidized ReducedOxidizing

AgentReducing

Agent

a. K � I2 → 2KI

b. 2Na � 2H2O → 2NaOH � H2

c. H2 � CuO → Cu � H2O

d. Cu(NO3)2 � Mg → Μg(ΝΟ3)2 � Cu

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32. Use the half-reaction method to balance the equations given below. Show allyour work.

a. HNO2 � HI y I2 � NO � H2O

b. K2Cr2O7 � FeCl2 � HCl y CrCl3 � KCl � FeCl3 � H2O

D. Essay33. Explain why oxidation cannot occur without reduction, and vice versa.

Name ___________________________ Date ___________________ Class __________________©

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05 ctr ch20 7/12/04 8:17 am page 517 the meaning of...

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