2. Chapter Menu Electrochemistry Section 20.1 Voltaic Cells
Section 20.2 Batteries Section 20.3 Electrolysis Exit Click a
hyperlink or folder tab to view the corresponding slides. 3.
Section 20-1 Section 20.1Voltaic Cells
- Describea way to obtain electrical energy from a redox
reaction.
oxidation:the loss of electrons from the atoms of a substance;
increases an atoms oxidation number
- Identifythe parts of a voltaic cell, and explain how each part
operates.
- Calculatecell potentials, and determine the spontaneity of
redox reactions.
reduction:the gain of electrons by the atoms of a substance;
decreases the atoms oxidation number 4. Section 20-1 Section
20.1Voltaic Cells(cont.) salt bridge electrochemical cell voltaic
cell half-cell In voltaic cells, oxidation takes place at the
anode, yielding electrons that flow to the cathode, where reduction
occurs. anode cathode reduction potential standard hydrogen
electrode 5. Section 20-1 Redox in Electrochemistry
- Electrochemistry is the study of the redox processes by which
chemical energy is converted to electrical energy and vice
versa.
- Redox reactions involve a transfer of electrons from the
species that is oxidized to the species that is reduced.
6. Section 20-1 Redox in Electrochemistry(cont.) 7. Section 20-1
Redox in Electrochemistry(cont.)
- Asalt bridgeis a pathway to allow the passage of ions from one
side to another, so that ions do not build up around the
electrodes.
- Anelectrochemical cell is an apparatus that uses a redox
reaction to produce electrical energy or uses electrical energy to
cause a chemical reaction.
8. Section 20-1 Redox in Electrochemistry(cont.)
- Avoltaic cellis a type of electrochemical cell that converts
chemical energy to electrical energy by a spontaneous redox
reaction.
9. Section 20-1 Chemistry of Voltaic Cells
- An electrochemical cell consists of two parts calledhalf-cells
, in which the separate oxidation and reduction reactions take
place.
- The electrode where oxidation takes place is called theanode
.
- Thecathodeis the electrode where reduction occurs.
10. Section 20-1 Chemistry of Voltaic Cells(cont.)
- Electric potential energy is a measure of the amount of current
that can be generated from a voltaic cell to do work.
- Electric charge can flow between two points only when a
difference in electric potential energy exists between the two
points.
- A volt is a unit used to measure cell potentialthe force from
the difference in electric potential energy between two
electrodes.
11. Section 20-1 Calculating Electrochemical Cell Potentials
- The tendency of a substance to gain electrons is itsreduction
potential .
- When two half-reactions are coupled, the voltage generated
corresponds to the difference in potential between the
half-reactions.
12. Section 20-1 Calculating Electrochemical Cell
Potentials(cont.)
- Thestandard hydrogen electrodeconsists of a small sheet of
platinum immersed in a hydrochloric acidsolution that has ahydrogen
ionconcentration of 1M .Hydrogen gas (H 2 ), at apressure of 1 atm,
isbubbled in and thetemperature is maintained at 25C.
13. Section 20-1 Calculating Electrochemical Cell
Potentials(cont.)
- The standard hydrogen electrode is the standard against which
all other reduction potentials are measured.
14. Section 20-1 Calculating Electrochemical Cell
Potentials(cont.) 15. Section 20-1 Calculating Electrochemical Cell
Potentials(cont.)
- Formula for cell potential
- E 0 cell=E 0 reduction E 0 oxidation
16. Section 20-1 Use Standard Reduction Potentials
- Cell potentials can be used to determine if a proposed reaction
under standard conditions will be spontaneous.
- If the calculated potential is positive, the reaction is
spontaneous.
- If the calculated potential is negative, the reaction is not
spontaneous.
17.
Section 20-1 Section 20.1 Assessment In electrochemistry, the
site where oxidation occurs is called ____.A. electrode B. anode C.
cathode D. ion 18.
Section 20-1 Section 20.1 Assessment The standard potential of a
voltaic cell is the difference between the:A. electrode voltage B.
standard reduction potentialof the cell and hydrogen C. standard
reduction potentialsof the half-cell reactions D. half-cell
reactions and thesalt bridge 19. End of Section 20-1 20. Section
20-2 Section 20.2Batteries
- Describethe structure, composition, and operation of the
typical carbon-zinc dry-cell battery.
reversible reaction:a reaction that can take place in both the
forward and reverse directions
- Distinguishbetween primary and secondary batteries, and give
two examples of each type.
- Explainthe structure and operation of the hydrogen-oxygen fuel
cell.
- Describethe process of corrosion of iron and methods to prevent
corrosion.
21. Section 20-2 Section 20.2Batteries(cont.) battery dry cell
primary battery secondary battery Batteries are voltaic cells that
use spontaneous reactions to provide energy for a variety of
purposes. fuel cell corrosion galvanization 22. Section 20-2 Dry
Cells
- Abatteryis one or more voltaic cells in a single package that
generates electric current.
23. Section 20-2 Dry Cells(cont.)
- Adry-cell is an electrochemical cell in which the electrolyte
is a moist paste. The paste in a zinc-carbon cell consists of zinc
chloride, manganese(IV) oxide, ammonium chloride, and a small
amount of water.
- The anode is the zinc shell.
- The cathode is a carbon rod, but reduction occurs in the
paste.
24. Section 20-2 Dry Cells(cont.)
- In the alkaline cell, zinc is in a powdered form and mixed with
potassium hydroxide contained in a steel case.
- Alkaline batteries are small and more useful in small
devices.
25. Section 20-2 Dry Cells(cont.)
- Silver batteries are similar to alkaline but smaller.
26. Section 20-2 Dry Cells(cont.)
- Primary batteriesproduce electric energy by means of redox
reaction that are not easily reversed.
- Secondary batteries depend on reversible redox reactions and
are rechargeable.
27. Section 20-2 Lead-Acid Storage Battery
- Lead-acid storage batteries are common in automobiles.
- The electrolyte solution is sulfuric acid, hence the name.
- The anode consists of grids of porous lead.
- The cathode consists of lead grids filled with lead(IV)
oxide.
28. Section 20-2 Lithium Batteries
- Lithium is the lightest known metal and has the lowest standard
reduction potential of the metallic elements.
- Lithium batteries can be either primary or secondary.
29. Section 20-2 Fuel Cells
- Afuel cellis a voltaic cell in which the oxidation of a fuel is
used to produce electric energy.
30. Section 20-2 Fuel Cells(cont.)
- Potassium hydroxide is often the electrolyte.
- The oxidation half reaction
- 2H 2 (g) + 4OH -> 4H 2 O + 4e
- The reduction half reaction
- O 2 (g) + 2H 2 O(l) + 4e -> 4OH (aq)
- When combined, the equation is the same as burning hydrogen in
oxygen to form water.
31. Section 20-2 Corrosion
- Corrosion is the loss of metal resulting from an
oxidation-reduction reaction of the metal with substances in the
environment.
- Rusting begins in a chip or pit in the iron surface, which
become the anode.
- Iron(II) becomes part of the water solution.
32. Section 20-2 Corrosion(cont.)
- The cathode is usually at the edge of the water drop where
water, iron, and air come into contact.
- The reduction reaction is O 2 (g) + 4H + (aq)+ 4e -> 2H 2
O(l).
- Next the oxidation 4Fe 2+ (aq) + 2O 2 (g) + 2H 2 O(l) + 4e
-> 2Fe 2 O 3 (s) + 4H + .
- Rusting is slow, but salts speed the process.
33. Section 20-2 Corrosion(cont.) 34. Section 20-2
Corrosion(cont.)
- Paint and other covers seal out moisture to prevent
corrosion.
- Blocks of metal that are more easily oxidized than steel, such
as magnesium, aluminum, or titanium, are often attached to the
hulls of shipsthey corrode while the iron in the hull is
protected.
35. Section 20-2 Corrosion(cont.)
- Galvanizationis the process of coating iron with a layer or
zinc.
- Zinc oxidizes at the surface, creating a layer of metal-oxide
that protects from further corrosion.
36.
Section 20-2 Section 20.2 Assessment Which type of battery has a
reversible spontaneous reaction? A. alkaline battery B. secondary
battery C. primary battery D. zinc-carbon battery 37.
Section 20-2 Section 20.2 Assessment Which is NOT a method of
preventing corrosion?A. painting B. galvanization C. coating with
electrolytes D. sacrificial anode 38. End of Section 20-2 39.
Section 20-3 Section 20.3Electrolysis
- Describehow it is possible to reverse a spontaneous redox
reaction in an electrochemical cell.
redox reaction:an oxidation-reduction reaction electrolysis
electrolytic cell
- Comparethe reactions involved in the electrolysis of molten
sodium chloride with those in the electrolysis of brine.
- Discussthe importance of electrolysis in the smelting and
purification of metals.
In electrolysis, a power source causes nonspontaneous reactions
to occur in electrochemical cells. 40. Section 20-3 Reversing Redox
Reactions
- The use of electrical energy to bring about a chemical reaction
is calledelectrolysis .
- An electrochemical cell in which electrolysis occurs is called
anelectrolytic cell .
41. Section 20-3 Applications of Electrolysis
- Electrolysis of water is one method of obtaining hydrogen gas
for commercial use.
42. Section 20-3 Applications of Electrolysis(cont.)
- Electrolysis can separate molten sodium chloride into sodium
metal and chlorine gas in a chamber called a Downs cell.
43. Section 20-3 Applications of Electrolysis(cont.)
- In the decomposition of brine, an aqueous solution of NaCl,
electrolysis is used to produce hydrogen gas, chlorine gas, and
sodium hydroxide.
44. Section 20-3 Applications of Electrolysis(cont.)
- The Hall-Hroult process requires large amounts of energy, which
is the primary reason for recycling aluminum.
45. Section 20-3 Applications of Electrolysis(cont.)
- Objects can be electroplated with a metal such as silver.
- The cathode is the object to be electroplated, where reduction
occurs.
- The anode is a bar of silver, where silver is oxidized and
silver ions transferred to the cathode.
46.
Section 20-3 Section 20.3 Assessment Which of the following is
NOT a product of electrolysis of brine?A. Chlorine gas B. Hydrogen
gas C. Sodium hydroxide solution D. Sodium metal 47.
Section 20-3 Section 20.3 Assessment What is required to drive a
nonspontaneous reaction in an electrolytic cell?A. electrodes B.
additional ions C. an energy source D. an electrolyte 48. End of
Section 20-3 49. Resources Menu Chemistry Online Study Guide
Chapter Assessment Standardized Test Practice Image Bank Concepts
in Motion 50. Study Guide 1 Section 20.1Voltaic Cells Key
Concepts
- In a voltaic cell, oxidation and reduction take place at
electrodes separated from each other.
- The standard potential of a half-cell reaction is its voltage
when paired with a standard hydrogen electrode under standard
conditions.
- The reduction potential of a half-cell is negative if it
undergoes oxidation when connected to a standard hydrogen
electrode. The reduction potential of a half-cell is positive if it
undergoes reduction when connected to a standard hydrogen
electrode.
51. Study Guide 1 Section 20.1Voltaic Cells(cont.) Key
Concepts
- The standard potential of a voltaic cell is the difference
between the standard reduction potentials of the half-cell
reactions.
52. Study Guide 2 Section 20.2Batteries Key Concepts
- Primary batteries can be used only once; secondary batteries
can be recharged.
- When a battery is recharged, electric energy supplied to the
battery reverses the direction of the batterys spontaneous
reaction.
- Fuel cells are batteries in which the substance oxidized is a
fuel from an external source.
- Methods of preventing corrosion are painting, coating with
another metal, or using a sacrificial anode.
53. Study Guide 3 Section 20.3Electrolysis Key Concepts
- In an electrolytic cell, an outside source of power causes a
nonspontaneous redox reaction to occur.
- The electrolysis of molten sodium chloride yields sodium metal
and chlorine gas. The electrolysis of brine yields hydrogen gas,
sodium hydroxide, and chlorine gas.
- Metals such as copper are purified in an electrolytic
cell.
- Electrolysis is used to electroplate objects and to produce
pure aluminum from its ore.
54.
Chapter Assessment 1 A salt bridge is used for what? A.
electrolysis B. allowing ions to move fromone half-cell to the
other C. increasing the reductionpotential D. linking multiple
voltaic cellstogether 55.
Chapter Assessment 2 Batteries that can be used more than once
are also called ____. A. primary batteries B. secondary batteries
C. tertiary batteries D. fuel cells 56.
Chapter Assessment 3 Corrosion is loss of metal by what
mechanism? A. electrolysis B. galvanization C. oxidation-reduction
reaction D. salt bridge 57.
Chapter Assessment 4 Electrolysis of H 2 O results in what
products? A. H +and OH B. H 2 O 2and O 2 C. NaOH and H 2 D. H 2and
O 2 58.
Chapter Assessment 5 Which of the following is NOT a dry-cell?A.
a car battery B. a silver battery C. a zinc-carbon battery D. an
alkaline battery 59.
STP 1 Which is NOT a characteristic of an acid? A. sour taste B.
conduct electricity in solution C. reactivity with some metals D.
slippery feel 60.
STP 2 Which metal has the lowest standard reduction potential?
A. Sodium B. Magnesium C. Lithium D. Silver 61.
STP 3 Which statement is NOT true about batteries? A. Batteries
are composed of twohalf-cells. B. Secondary batteries are alsoknown
as storage batteries. C. Redox reactions in zinc-carbonbatteries
are easily reversible. D. Batteries are compact forms ofvoltaic
cells. 62.
STP 4 Which of the following is the equation used to calculate a
cell potential? A. E 0 cell=E 0 oxidation E 0 reduction B. E 0
cell=E 0 reduction E 0 oxidation C. E 0 cell=E 0 reduction+ E 0
oxidation D. E 0 cell=E 0 reduction xE 0 oxidation 63.
STP 5 Which is NOT an example of a sacrificial anode?A.
magnesium B. aluminum C. iron D. titanium 64. IB Menu Click on an
image to enlarge. 65. IB 1 66. IB 2 67. IB 3 68. IB 4 69. IB 5 70.
IB 6 71. IB 7 72. IB 8 73. IB 9 74. IB 10 75. IB 11 76. IB 12 77.
IB 13 78. IB 14 79. IB 15 80. IB 16 81. IB 17 82. IB 18 83. IB 19
84. CIM Figure 20.2Voltaic Cells 85. Help Click any of the
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