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Study Guide for Content Mastery Chemistry: Matter and Change • Chapter 21 121

ElectrochemistryElectrochemistry

Section 21.1 Voltaic CellsIn your textbook, read about redox in electrochemistry.

Use each of the terms below just once to complete the passage.

Oxidation and reduction reactions can occur in separate solutions, as long as there are two

connections between the solutions. One connection is a(n) (1)

through which ions can flow. The other connection is a metal wire through which electrons

can flow. The flow of ions or electrons is known as a(n) (2) . The

complete setup, called a(n) (3) , can convert chemical energy into

electrical energy or electrical energy into chemical energy. These cells are also known as

(4) cells or (5) cells.

Use the diagram of an electrochemical cell to answer the following questions.

6. The equation at the bottom of each beaker shows the half-reaction that is occurring in that beaker. What kind of reaction(oxidation or reduction) is occurring in each beaker?

Left beaker

Right beaker

7. Write the net ionic equation for this electrochemical cell.

8. In which direction do electrons move through the wire?

9. What kind of ions (positive or negative) move from the �-shaped tube into each beaker?

Left beaker Right beaker

STUDY GUIDE FOR CONTENT MASTERYCHAPTER 21

voltaic electrochemical cell electric current salt bridge galvanic

Wire

Ions Ions

Pt2� � 2e� 0 Pt Ni 0 Ni2� � 2e�

Pt Ni

Cl� K�

Cl�K�

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122 Chemistry: Matter and Change • Chapter 21 Study Guide for Content Mastery

In your textbook, read about the chemistry of voltaic cells.

For each item in Column A, write the letter of the matching item in Column B.

Column A Column B

10. One of the two parts of an electrochemical cell, whereeither oxidation or reduction takes place

11. An electrode where oxidation takes place

12. An electrode where reduction takes place

13. One or more electrochemical cells in a single package thatgenerates electrical current

14. A measure of the amount of current that can be generatedfrom an electrochemical cell to do work

In your textbook, read about calculating cell electrochemical potential.

Circle the letter of the choice that best completes the statement or answers the question.

15. The tendency of an electrode to gain electrons is called

a. electron potential. c. reduction potential.

b. gravitational potential. d. oxidation potential.

16. A sheet of platinum covered with finely divided platinum particles is immersed in a 1M HCl solution containing hydrogen gas at a pressure of 1 atm and a temperature of25°C. The platinum sheet is known as a

a. standard platinum electrode. c. hydrogen chloride electrode.

b. standard hydrogen electrode. d. platinum chloride electrode.

17. The standard reduction potential of a half-cell is a measure of

a. concentration. c. temperature.

b. pressure. d. voltage.

18. Which of the following is the correct way to represent the equation,H2(g) + Cu2�(aq) 0 2H�(aq) � Cu(s)?

a. H2�H��Cu2��Cu c. Cu2��Cu�H2�H�

b. H��H2�Cu�Cu2� d. Cu�Cu2��H��H2

19. When connected to a hydrogen electrode, an electrode with a negative standard reductionpotential will carry out

a. reduction. c. both oxidation and reduction.

b. oxidation. d. neither oxidation nor reduction.

Section 21.1 continued


a. battery

b. electrical potential

c. half-cell

d. cathode

e. anode

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In your textbook, read about calculating cell electrochemical potential.

Use the table of standard reduction potentials below to answer the following questions.

20. Suppose you have two voltaic cells whose half-cells are represented by the followingpairs of reduction half-reactions. For each voltaic cell, identify which half-reaction willproceed in the forward direction as a reduction and which will proceed in the reversedirection as an oxidation.

Voltaic Cell #1 Voltaic Cell #2

Al3�(aq) � 3e� 0 Al(s) Tl3�(aq) � 3e� 0 Tl(s)

Ga3�(aq) � 3e� 0 Ga(s) Ga3�(aq) � 3e� 0 Ga(s)

21. Calculate the cell standard potential, E0cell, of each voltaic cell in question 20.

Voltaic Cell #1:

Voltaic Cell #2:

In your textbook, read about using standard reduction potentials.

Use the table of standard reduction potentials at the top of this page to answer the fol-lowing questions.

22. Write the reduction and oxidation half-reactions for the following reaction:

Tl(s) � Al3�(aq) 0 Tl3�(aq) � Al(s)

reduction half-reaction:

oxidation half-reaction:

23. What is the standard reduction potential, E0, for each half-reaction in question 22?

E0reduction: E0

oxidation:

24. Calculate the cell standard potential, E0cell, for the reaction in question 22.

25. Will the reaction in question 22 occur spontaneously as written? Explain why or why not.

26. Will the reverse reaction, Tl3�(aq) � Al(s) 0 Tl(s) � Al3�(aq), occur spontaneously?Explain why or why not.



Half-reaction E0 (volts)

Al3� � 3e� 0 Al �1.662

Ga3� � 3e� 0 Ga �0.549

Tl3� � 3e� 0 Tl �0.741

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Section 21.2 BatteriesIn your textbook, read about dry cells, the lead–acid storage battery, and lithium batteries.

Complete the table below by writing the type of battery described on the right. Chooseyour answers from the following types: lead–acid battery, lithium battery, mercury battery,nickel–cadmium battery, zinc–carbon dry cell.

In the space at the left, write true if the statement is true; if the statement is false,change the italicized word or phrase to make it true.

6. In a zinc–carbon dry cell, a carbon rod serves as the cathode.

7. Secondary batteries produce electric energy by means of redoxreactions that are not easily reversed.

8. One advantage of alkaline cells is that they are larger than drycells.

9. When a lead–acid battery is generating electric current, sulfuricacid is consumed and lead(II) sulfate is produced.

10. Dry cells, alkaline cells, and mercury batteries are examples ofprimary batteries.

11. Compared to most other batteries, lithium batteries store a smallamount of energy for their size.

12. Secondary batteries are rechargeable.

13. Each cell in a lead–acid battery generates about 12 volts.

14. In a mercury battery, liquid mercury is reduced, forming mercuryoxide.

15. Lead–acid batteries and nickel–cadmium batteries are examples ofsecondary batteries.


Type of Battery Description

1. Often used to power hearing aids and calculators because of its small size

2. The standard, rechargeable automobile battery

3. Often used in cordless drills, screwdrivers, and shavers because it is compact and rechargeable

4. The most commonly used voltaic cell from the 1880s until recently

5. Lightweight, long-lasting battery often used in watches and computers to maintain time and date settings

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In your textbook, read about fuel cells.

Circle the letter of the choice that best completes the statement or answers the question.

16. The main purpose of a fuel cell is to produce

a. fuel. b. electric energy. c. chemical energy. d. heat.

17. In the hydrogen–oxygen fuel cell,

a. hydrogen is oxidized and oxygen is reduced. c. both oxygen and hydrogen are oxidized.

b. oxygen is oxidized and hydrogen is reduced. d. both oxygen and hydrogen are reduced.

18. What is the main difference between the reaction in a hydrogen–oxygen fuel cell and theburning of hydrogen in air?

a. When hydrogen burns in air, the oxidation and reduction reactions are separated.

b. The burning of hydrogen in air does not produce water.

c. The reaction in a fuel cell does not produce water.

d. The reaction in a fuel cell is very controlled.

In your textbook, read about corrosion.

Use the diagram below to answer the following questions.

19. What is the function of the sacrificial anode?

20. Name one metal that is commonly used as a sacrificial anode.

21. Galvanizing the iron tank (or pipe) would serve the same function as a sacrificial anode.What is galvanizing?

22. In what two ways does galvanizing protect iron?

Undergroundiron storage

tank

Sacrificial anode Wire



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Section 21.3 ElectrolysisIn your textbook, read about reversing redox reactions and electrolysis.

In the space at the left, write the word or phrase in parentheses that correctly completesthe statement.

1. When a battery is being recharged, its redox reaction is reversedand energy is (absorbed, released) by the battery.

2. The use of electrical energy to cause a chemical reaction is called(combustion, electrolysis).

3. An electrochemical cell in which electrolysis is occurring is calledan (electrolytic, exothermic) cell.

4. In a Down’s cell, sodium metal and chlorine gas are producedfrom (molten, solid) sodium chloride.

5. The electrolysis of brine involves applying current to an aqueoussolution of (hydrochloric acid, sodium chloride).

6. The commercially important products of the electrolysis of brineare hydrogen gas, chlorine gas, and (oxygen gas, sodiumhydroxide).

In your textbook, read about the purification of metallic ores, electroplating, and aluminum manufacture.

Answer the following questions.

7. Copper can be produced by heating Cu2S in the presence of oxygen. Why must the copper then be subjected to electrolysis?

8. When an object is electroplated with silver, what is the anode and what is the cathode?

anode

cathode

9. The manufacture of aluminum begins with the electrolysis of aluminum oxide, Al2O3.What half-reaction occurs at the cathode?

10. Why are plants that produce aluminum often built close to large hydroelectric power stations?


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