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Chapter 16
Oxidation and Reduction

16-04
Title
Definitions of oxidation and reduction
Caption
In a redox reaction, one substance loses electrons, while the other substance gains electrons.
Notes
Every redox reaction involves both a substance which loses electrons, and a substance which gains electrons.
Keywords
oxidation, reduction, electron, reaction
16-04-01un
Title
Determining the element undergoing oxidation and reduction
Caption
The element undergoing oxidation is the one which assumes a more positive oxidation state when going from reactants and products. The element undergoing reduction is the one which assumes a more negative oxidation state when going from reactants and products.
Notes
In this example, C is oxidized, and S is reduced.
Keywords
oxidation, reduction, electron, reaction, oxidation state
16-04-03un
Title
Determining the elements undergoing oxidation and reduction
Caption
The element undergoing oxidation is the one which assumes a more positive oxidation state when going from reactants and products. The element undergoing reduction is the one which assumes a more negative oxidation state when going from reactants and products.
Notes
In this example, Ca undergoes oxidation, and hydrogen is reduced. Note that oxygen's oxidation state remains unchanged (-2) throughout.
Keywords
oxidation, reduction, electron, reaction, oxidation state
16-04-04un
Title
Determining the elements undergoing oxidation and reduction: Example 16.5
Caption
The element undergoing oxidation is the one which assumes a more positive oxidation state when going from reactants and products. The element undergoing reduction is the one which assumes a more negative oxidation state when going from reactants and products.
Notes
In this example, Al undergoes oxidation, and Cu is reduced. The element with higher electronegativity is normally the one to be reduced.
Keywords
oxidation, reduction, electron, reaction, oxidation state
16-04-05un
Title
Determining the elements undergoing oxidation and reduction: Example 16.6
Caption
The element undergoing oxidation is the one which assumes a more positive oxidation state when going from reactants and products. The element undergoing reduction is the one which assumes a more negative oxidation state when going from reactants and products.
Notes
In this example, Fe undergoes oxidation, and MnO4- is reduced. The element with higher electronegativity is normally the one to be reduced.
Keywords
oxidation, reduction, electron, reaction, oxidation state
16-04-06un
Title
Balancing Redox Reactions: Example 16.7
Caption
Balancing redox reactions works like balancing other reactions seen in this course, with attention paid to the charge balance.
Notes
In this case, the half reactions must be multiplied so that the number of electrons to the left of the arrow equals the number of electrons to the right of the arrow. The half-reaction 2 I- --> I2 + 2 e- must be multiplied by 3 to match the electrons in the half reaction, 6 e- + 14 H+ + Cr2O72- --> 2 Cr3+ + 7 H2O.
Keywords
oxidation, reduction, electron, reaction, oxidation state, half-reaction, charge
16-05
Title
Magnesium is oxidized to Mg2+
Caption
When a magnesium strip is put into a Cu2+ solution, the magnesium is oxidized to Mg2+ and the copper is reduced to Cu(s). Notice the fading of the blue color (due to Cu2+ ions) in solution and the appearance of solid copper on the magnesium electrode.
Notes
Magnesium has lower electronegativity than copper: It will give up its valence electrons to the copper ions in the blue copper(II) sulfate solution.
Keywords
oxidation, reduction, electron, reaction, oxidation state, copper, magnesium
16-11
Title
Voltage is analogous to a river's path
Caption
A high voltage for electricity is analogous to a steep landscape for a river.
Notes
The steeper the riverbed, the greater the potential for water to flow. Likewise, high voltage means that there is a greater potential for electrons to move.
Keywords
oxidation, reduction, electron, reaction, oxidation state, voltage
16-13
Title
Common dry cell battery
Caption
The battery produces electricity by the reaction of zinc, found in the battery's case, and MnO2, found in the battery's interior paste.
Notes
The half reactions are, Zn --> Zn2+ + 2 e- (anode; oxidation) 2 MnO2 + 2 NH4+ + 2 e- --> Mn2O3 + 2 NH3 + H2O (cathode; reduction)
Keywords
oxidation, reduction, electron, reaction, oxidation state, voltage, half-reaction, battery, anode, cathode
16-14
Title
Lead-acid storage battery
Caption
Why do batteries like this become depleted? How are they recharged?
Notes
As the battery is used, the Pb and PbO2 are converted to PbSO4. By applying an electric current to the battery, the PbSO4 takes up the current's energy to convert it back into Pb and PbO2.
Keywords
oxidation, reduction, electron, reaction, oxidation state, voltage, half-reaction, battery, anode, cathode
16-15
Title
A hydrogenÐoxygen fuel cell
Caption
Fuel cells operate much like batteries, but the reactants are replenished continuously.
Notes
The hydrogenÐoxygen fuel cell is the most common type. The overall reaction is, 2 H2 + O2 --> 2 H2O HydrogenÐoxygen fuel cells are attractive, because they produce no pollutants; water is the only product.
Keywords
oxidation, reduction, electron, reaction, oxidation state, voltage, half-reaction, fuel cell, anode, cathode
16-16
Title
Schematic diagram of a fuel-cell breathalyzer
Caption
A breathalyzer fuel cell produces a measurable current from the reaction of alcohol and oxygen.
Notes
The electronics of the breathalyzer convert the measured current to an equivalent blood alcohol concentration.
Keywords
oxidation, reduction, electron, reaction, oxidation state, voltage, half-reaction, fuel cell, anode, cathode
16-18
Title
Electrolytic cell for silver plating
Caption
Silver is oxidized on the left side of the cell and reduced at the right. As it is reduced, it plates on the object to be plated.
Notes
When electrons are supplied to the cathode, silver ion plates out as metallic silver. At the anode, the electrons are drawn out of the silver metal electrode, producing silver ions, that go into the solution.
Keywords
oxidation, reduction, electron, reaction, oxidation state, voltage, half-reaction, fuel cell, anode, cathode, electrolytic cell
16-18-05un
Title
Balancing Redox Reactions: Example 16.13
Caption
Balancing redox reactions works like balancing other reactions seen in this course, with attention paid to the charge balance.
Notes
In this case, the half reactions must be multiplied so that the number of electrons to the left of the arrow equals the number of electrons to the right of the arrow.
Keywords
oxidation, reduction, electron, reaction, oxidation state, half-reaction, charge
16-18-06i
Title
Aluminum atoms and copper ions: Chapter 16, Problem 101
Caption
What happens to the atoms and ions if the Al strip is dipped into the copper ion solution?
Notes
Copper metal will plate out, while Al3+ ions will begin to populate the solution.
Keywords
oxidation, reduction, electron, reaction, oxidation state, copper, aluminum
16-18-07j
Title
An electrochemical cell: Chapter 16, Problem 103
Caption
How might this cell appear after it has generated a substantial amount of electrical current?
Notes
We expect the Zn strip to be much smaller, and the left beaker to contain a higher concentration of zinc ions. Nickel would plate out on the metal strip in the right beaker, and there would be a lower concentration of nickel ions in the solution.
Keywords
oxidation, reduction, electron, reaction, oxidation state, voltage, half-reaction, fuel cell, anode, cathode, electrolytic cell

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