CHAPTER

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CHAPTER 8Chemistry for Changing Times

• Oxidation and Reduction
• Burn and Unburn

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Why Should We Be Interested In Oxidation-Reduction
Reactions?

• Cells obtain energy by oxidizing foods.
• Green plants, using sunlight, produce foods by
  reduction of carbon dioxide.
• Extraction of metals from ores by reduction.
• Metals corrode by oxidation.
• Technology depends on oxidizing fossil fuels
  (coal, natural gas and petroleum) to obtain
  chemical energy which was primarily stored in
  them by the fossilization of green plants.
• Oxidation-reduction reactions can be used to
  produce electricity batteries and cells.

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What Are Some General Characteristics of
Oxidation-Reduction Reactions?

• Oxidation-reduction redox reactions.
• One does not occur without the other when one
  substance is oxidized the other is reduced.
• They occur simultaneously although we may speak
  of them separately.
• They occur in exactly equivalent amounts.
• They are opposite aspects of the same process.
• Reduced forms of matter food, coal and gasoline
  are high in energy.
• Oxidized forms CO2 and H2O are low in energy.

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How Are Redox Reactions Explained? Three Views

• View 1 Oxidation is a gain of oxygen atoms
  Reduction is a loss of oxygen atoms.
• Methane burned
• CH4 2O2 CO2 2H2O.
• Both carbon and hydrogen gain oxygen oxidized.
• Lead dioxide heated
• 2PbO2 2PbO O2.
• Lead dioxide loses an oxygen reduced.
• Burning hydrogen
• 2H2 O2 2 H2O
• Hydrogen is oxidized it gains oxygen.

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Redox Problems 1

• In each of the following reactions, is the
  reactant undergoing oxidation or reduction?
  (These are not complete chemical reactions)
• Pb PbO2
• SnO2 SnO
• KClO3 KCl
• Cu2O 2CuO

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Redox Problems 1 -Answers

• In each of the following reactions, is the
  reactant undergoing oxidation or reduction?
  (These are not complete chemical reactions)
• Pb PbO2 oxidized (gains oxygen)
• SnO2 SnO reduced (loses 1 oxygen)
• KClO3 KCl reduced (loses 3 oxygens)
• Cu2O 2CuO oxidized (Cu gains oxygen)

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How Are Redox Reactions Explained? Three Views

• View 2 Oxidation is a loss of hydrogen atoms
  Reduction is a gain of hydrogen atoms.
• Suppose both reactants gain oxygen atoms?
• Methane burned.
• CH4 2O2 CO2 2H2O.
• Oxygen gains hydrogen reduced.
• Carbon loses hydrogen oxidized.

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Redox Problems 2

• In each of the following reactions, is the
  reactant undergoing oxidation or reduction? (
  Some may not be complete equations)
• CH3OH (methyl alcolol) CH2O (formaldehyde)
  H2
• CO 2H2 CH3OH
• C2H6O C2H4O
• C2H2 C2H6

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Redox Problems 2- Answers

• In each of the following reactions, is the
  reactant undergoing oxidation or reduction? (
  Some may not be complete equations)
• CH3OH (methyl alcohol) CH2O formaldehyde)
  H2 oxidized (loses 2 Hs)
• CO 2H2 CH3OH reduced (gains 3 Hs)
• C2H6O C2H4O oxidized (loses 2 Hs)
• C2H2 C2H6 reduced (gains 4 Hs)

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How Are Redox Reactions Explained? Three Views

• View 3 Ion formation Oxidation is a loss of
  electrons Reduction is a gain of electrons.
• Electrons are passed from one chemical species to
  another energy.
• The charge on an ion is often referred to as the
  oxidation number.
• oxidation if a positive charge loss of
  electrons oxidized.
• electrons reduced.

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Mg Cl2 Mg2 2Cl-. Mg atom 0
charge. Mg ion 2 charge loss of 2 electrons
oxidized oxidation number (plus). Cl atom
0 charge. Cl ion 1- charge gain of 2
electrons reduced 15
Redox Problems 3

• In the following reactions, is the reactant
  undergoing oxidation of reduction? (These are not
  complete chemical reactions)
• Zn Zn2
• Fe3 Fe2
• S2- S

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Redox Problems 3- Answers

• In the following reactions, is the reactant
  undergoing oxidation of reduction? (These are not
  complete chemical reactions)
• Zn Zn2 oxidized (loses 2 electrons)
• Fe3 Fe2 reduced (gains 1 electron)
• S2- S oxidized (loses 2 electrons)

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Why 3 Views of Redox Reactions?

• Gain and loss of oxygen is historical and
  specific.
• Definition in terms of electrons applies more
  broadly.
• Which view should be used?
• Whichever is clearest or most convenient.
• C O2 CO2 gain oxygen oxidized
• CH2O H2 CH4O gain hydrogen reduced
• 3Sn2 2Bi3 3Sn4 2 Bi tin is
  oxidized oxidation number bismuth is reduced
  
• Remember LEO the lion says GER!
• Lose Electrons Oxidized.
• Gain Electrons Reduced.

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Identifying Redox Reactions

• When magnesium metal reacts with chlorine gas,
  magnesium ions and chloride ions are formed
• Mg Cl2 MgCl2
• MgCl2 ionizes Mg2 2Cl-
• Mg goes from 0 to 2 oxidation number
  oxidized
• Cl goes from 0 to 1 reduced

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What Is the Significance of Oxidizing Agents in
Redox Reactions?

• Every redox reaction has an oxidizing agent and
  reducing agent among the reactants.
• Oxidizing agent substance being reduced and
  causing
• oxidization.
• CuO H2 Cu H2O.
• CuO causes H2 to be oxidized CuO is an
  oxidizing agent.
• Hydrogen causes CuO to reduced H2 is the
  reducing agent.

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What Is the Significance of Oxidizing Agents in
Redox Reactions?

• .
• Oxygen is the most common oxidizing agent.
• 1/5 of air.
• 1 of 2 dozen elements essential to life.
• 2/3 of body mass oxygen.
• ½ accessible portion of earth mass.
• Found in all 3 subdivisions of Earths structure.
• Atmosphere 21 oxygen.

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What Is the Significance of Oxidizing Agents in
Redox Reactions?

• Functions of oxygen as an oxidizing agent.
• Burns wood and gasoline combustion.
• Burns the food we eat oxidation.
• Causes corrosion, food spoilage and wood decay.
• Oxidation and combustion need for oxygen to
  burn energy source for release of stored energy.
• Supplies 86 of energy that supports
  civilization.
• 21 billion kg produced/year in US for industrial
  use.
• Produced by liquifying air at very low
  temperatures.

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What Is the Significance of Oxidizing Agents in
Redox Reactions?

• Ozone powerful oxidizing agent and air
  pollutant with both good and bad effects.
• O2 diatomic but ozone is triatomic (O3
  ozone), in mesosphere
• 3O2 (g) O 2O3 (g) ozone.
• O3 in lower atmosphere irritates plants and
  animals plus destructive to rubber toxic
  (destroys biological molecules).
• A product found in photochemical smog.
• O3 in the outer atmosphere (stratosphere)
  protects against (adsorbs) harmful UV radiation
  making possible the evolution of advanced life.
• O3 (g) energy (UV) O2 (g) O (g).
• Ozone depletion in the stratosphere?
• Corrlelated with chlorofluorocarbons aerosol
  can CFCs.

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What Is the Significance of Oxidizing Agents in
Redox Reactions?

• Significance of other oxidizing agents.
• Breathalyzer tests utilized oxidation reactions.
• Potsssium dichromate (K2Cr2O7) can oxidize
  alcohol.
• Turns from yellow to green in proportion to
  amount of alcohol in breath.
• Antiseptics mild oxidizing agents.
• Applied to living tissue (wounds) to kill
  microorganisms or prevent their growth.
• Hydrogen peroxide.
• Tincture of iodine.
• Benzoyl peroxide acne treatment.

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What Is the Significance of Oxidizing Agents in
Redox Reactions?

• Significance of other oxidizing agents.
• Disinfectants oxidizing agents.
• Chlorine in drinking water and swimming pools
  kills diseasecausing bacteria.
• Bleaches oxidizing agents.
• Removal of unwanted color from materials.
• Laundry bleaches sodium hypochlorite (NaOCl) or
  calcium hypochlorite
• Lightening hair color.
• Hydrogen peroxide (6-12 solution).
• Oxidizes melanin pigment to a colorless product.

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What Is the Significance of Reducing Agents in
Redox Reactions?

• Reducing agent substance being oxidized.
• CuO H2 Cu H2O.
• H2 causes CuO to be reduced oxygen loss
  reducing agent.
• What is the value of reactions which initiate a
  reduction phenomena?
• Metals freed from ores involve reduction
  reactions.
• Metal compounds (ores) must be reduced to produce
  the free metal.
• Use of coke carbon from heating coal.
• Tin from tin oxide (C REDUCING AGENT)
• SnO2 C Sn CO2.
• Chromium from Cr oxide.
• Cr2O3 2Al Al2O3 2Cr.

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What Is the Significance of Reducing Agents in
Redox Reactions?

• Antioxidants reducing agents in food chemistry
  and life processes.
• Prevents browning (air oxidation) of fruit
  ascorbic acid (vitamin C) water soluble.
• Vitamin E and A are fat soluble antioxidants.
• Retard damaging oxidation reactions in living
  cells.
• Anticarcinogens.

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What Is the Significance of Reducing Agents in
Redox Reactions?

• Hydrogen as a reducing agent.
• Frees many metals from their ores.
• Used to free more expensive metals such as
  tungsten (W).
• WO3 3H2 W 3H2O.
• Can reduce many chemical compounds.
• Reduces nitrogen from air to produce ammonia.
• N2 3H2 2NH3.

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Redox Problems 4

• Identify the oxidizing and reducing agents in the
  following reactions.
• 2C O2 2CO
• SnO H2 Sn H2O
• Mg Cl2 Mg2 2Cl-

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Redox Problems 4 -Answers

• Identify the oxidizing and reducing agents in the
  following reactions.
• 2C O2 2CO C is RA O is OA
• SnO H2 Sn H2O Sn is OA H is RA
• Mg Cl2 Mg2 2Cl- Mg loses electrons
  and is RA Cl is OA

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How Are Redox Reactions Important To Our Lives?

• Electricity dry cell and storage batteries are
  based on redox reactions.
• Electrical current flow of electrons.
• Redox electrochemical reactions can produce
  electricity.
• Zn CuSO4 Zn2 (aq) Cu (s) SO42-
• Zn oxidized and Cu ions are reduced.
• Electrons transferred from Zn to Cu through a Cu
  wire electrical current. (Zn and Cu separated
  into different compartments connected by Cu wire)
  Zn readily gives off electrons compared with
  Cu.
• Run a motor or light a lamp.

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Redox Problems 5

• Half reactions electrochemical reactions are
  often represented as two half-reactions.
• Zn/Cu cell example overall reaction
• Zn (s) Cu2 (aq) Zn2 (aq) Cu (s)
• Half-reactions
• Oxidation Zn (s) Zn2 (aq) 2 e-
• Reduction Cu2 (aq) 2 e- Cu (s)
• Half-reactions to balanced overall reaction.
• The 2 e-s cancel out when the two half-reactions
  are added.

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Redox Problems 5

• Represent the following reaction as two
  half-reactions and label them as an oxidation
  half-reaction and a reduction half-reaction.
• Mg Cl2 Mg2 2Cl-

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Redox Problem 5 - Answer

• Represent the following reaction as two
  half-reactions and label them as an oxidation
  half-reaction and a reduction half-reaction.
• Mg Cl2 Mg2 2Cl-
• Oxidation Mg Mg2 2 e-
• Reduction Cl2 2 e- 2Cl-

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Redox Problem 7

• Label each of the following half-reactions as
  oxidation or reduction and then combine them to
  obtain a balanced overall redox reaction
• 2H2O2 2O2 4H 4 e-
• Fe3 e- Fe2

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Redox Problem 7 - Answer

• Step 1
• 2H2O2 2O2 4H 4 e- oxidation
• Fe3 e- Fe2 reducton
• Step 2
• Equalize the electrons in both half-reactions.
  Electrons lost by the substance being oxidized
  must be gained by the substance being reduced)
• 4(Fe3 e- Fe2 ) 4Fe3 4 e-
  4Fe2
• Step 3
• Formulate full balanced equation and check.
• 4Fe3 2H2O2 4Fe2 2O2 4H
• Fe 4 Fe 4
• H 4 H 4
• O 4 O 4

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How Are Redox Reactions Important To Our Lives?

• Corrosion - 2Fe O2 H2O 2Fe(OH)2 .
• Economic impact.
• 100 billion corrosive costs/year in US.
• 20 new steel needed to replace that lost through
  corrosion/year in US.

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How Are Redox Reactions Important To Our Lives?

• Corrosion.
• Aluminum. Why no rust?
• Same redox chemical reaction as with iron.
• Aluminum oxide hard and nonporous forms
  protective coat against further oxidation.
• Explosive reactions.
• Chemical explosion redox reaction rapid
  chemical reaction with considerable increase in
  volume.
• Nitrogen compounds are usually involved.
• Nitroglycerine dynamite.
• Ammonium nitrate fertilizer.
• Trinitrotoluene TNT.
• How can fertilizer and fuel oil react to create
  an enormous explosion?
• 1995 Oklahoma City, Alfred P Murrah Building
  worst terrorist bombing in US.

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How Are Redox Reactions Important To Our Lives?

• Explosive reactions.
• Ammonium nitrate-fuel oil (ANFO) mixture releases
  nitrogen gas rapidly.
• ANFO used in 1995 enormous power 2 tons in
  truck.
• Ammonium nitrate is both oxidized and reduced.
• Ammonium ion reducing agent.
• Nitrate ion oxidizing agent.
• Fuel oil provides additional oxidizable material.
• ANFO chemical reaction.
• 52NH4NO3 (s) C17H36 (L) 52N2 (g)
  17CO2 (g) 122H2O (g).
• Tremendous release of gaseous products great
  volume and very rapid explosion.
• Products easily obtained.

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Why Are Redox Reactions Essential To Life
Processes?

• Metabolism redox reactions that produce energy
  for life processes.
• Food production photosynthesis reduction
  process energy storage (food creation).
• Provides all food we need carbohydrate
  production.
• Only natural process that provides the oxygen
  that we breathe.
• Carbohydrates from photosynthesis ultimate
  source of all our food.
• All animals either eat plants or eat other
  animals that eat plants.
• Photosynthesis.
• 6CO2 6H2O energy from sun C6H12O6
  6O2.
• CO2 is reduced
• O2 is oxidized.

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Why Are Redox Reactions Essential To Life
Processes?

• Metabolism redox reactions that produce energy
  for life processes.
• Food oxidation oxidative process energy
  release (food breakdown) for carrying on life
  functions.
• Bread consumption carbohydrate oxidation.
• C6H12O6 (carbohydrate) 6O2 6CO2 6H2O
  energy.