Department of Chemistry

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• Department of Chemistry
• CHEM1010 General Chemistry
• Instructor Dr. Hong Zhang
• Foster Hall, Room 221
• Tel [phone]
• Email hzhang_at_tntech.edu

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CHEM1010/General Chemistry_______________________
__________________Chapter 8. (L31)-Oxidation and
Reduction

• Todays Outline
• ..Review of oxidants and reductants
• ..Hydrogen and reducing agents (reductants)
• Hydrogen
• Other common reductants
• ..Redox chemistry of living things
• Photosynthesis
• Respiration

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Chapter 8. (L31)-Oxidation and Reduction

• Oxidants and reductants
• Oxidation and reduction happen together (they
  are coupled).
• Example
• CuO H2 Cu H2O
• Cu 2 0 Cu is reduced
• H 0 1 H is oxidized
• CuO oxidizes H2, so CuO is the oxidant
  (oxidizing agent)
• H2 reduces CuO, so H2 is the reductant (reducing
  agent)

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Chapter 8. (L31)-Oxidation and Reduction

• Oxidants and reductants
• Oxidation and reduction happen together (they
  are coupled).
• Example
• C O2 CO2
• C 0 4 C is oxidized
• O 0 -2 O is reduced
• O2 oxidizes C, so O2 is the oxidant (oxidizing
  agent)
• C reduces O2, C is the reductant (reducing
  agent)

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Chapter 8. (L31)-Oxidation and Reduction

• Hydrogen An important reductant
• ..Hydrogen is 0.9 of outer accessible portion
  of the Earth by mass
• ..Unlike oxygen gas, hydrogen is seldom found as
  a free gas, but always combined with some
  elements, as in coal, petroleum, water, biomass
  as hydrocarbon
• ..Hydrogen is special, in Group IA, but not a
  metal, a unique element

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Chapter 8. (L31)-Oxidation and Reduction

• Hydrogen An important reductant
• ..Small amounts of hydrogen can be made by
• Zn(s) 2HCl ZnCl2 H2
• ..Commercial quantities of hydrogen are made as
  by-products of petroleum refining or by the
  reaction of natural gas with steam
• ..12 billion kg of hydrogen is produced each
  year in the USA, with 2/3 is used to produce NH3

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Chapter 8. (L31)-Oxidation and Reduction

• Hydrogen An important reductant
• ..Hydrogen can be a new fuel for powering cars
• O2 2H2 2H2O
• no pollution from the exhaust pipe
• Textbook ppxxvii
• hydrogen fuel cell cars, the future

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Chapter 8. (L31)-Oxidation and Reduction

• Hydrogen An important reductant
• ..Hydrogen is a very good reductant to free
  metals from their ores (e.g., metals oxides)
• Example
• WO3 3H2 W 3H2O
• W 6 0
• H 0 1
• 6 e- transfer from 3H2 to W

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Chapter 8. (L31)-Oxidation and Reduction

• Hydrogen An important reductant
• ..Hydrogen can also reduce many organic
  compounds
• Example
• C2H4 H2 C2H6
• ethylene ethane
• C -2 -3
• H 0 1
• 2 e- transfer from H2 to 2C

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Chapter 8. (L31)-Oxidation and Reduction

• Hydrogen An important reductant
• ..Hydrogen can also reduce inorganic gases
• Example
• N2 3H2 2NH3
• N 0 -3
• H 0 1
• 6 e- transfer from 3H2 to 2N

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Chapter 8. (L31)-Oxidation and Reduction

• Hydrogen An important reductant
• ..Hydrogen can also reduce inorganic gases
• Example
• O2 2H2 2H2O
• O 0 -2
• H 0 1
• 4 e- transfer from 2H2 to 2O
• Reactions of hydrogen with gases often needs
  catalysts such as Pt, Ni, because they can adsorb
  a large amount of hydrogen gas on their surfaces.

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Chapter 8. (L31)-Oxidation and Reduction

• Other common reducing agents (reductants)
• ..Carbon (e.g., in coal), commonly used to free
  metals from their oxides
• SnO2 C Sn CO2
• Sn 4 0
• C 0 4
• 4 e- transfer from C to Sn
• reductant C
• oxidant Sn in SnO2

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Chapter 8. (L31)-Oxidation and Reduction

• Other common reducing agents (reductants)
• ..Metals can also be made by heating metal
  oxides with another more active metal
• Cr2O3 2Al 2Cr Al2O3
• Cr 3 0
• Al 0 3
• 6 e- transfer from 2Al to Cr
• reductant Al
• oxidant Cr in Cr2O3

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Chapter 8. (L31)-Oxidation and Reduction

• Reduction in photography
• .. Developer used in black-and-white
  photography
• Film AgBr coated, upon exposed to light, the
  following reaction occurs
• C6H4(OH)2 2Ag light C6H4O2 Ag 2H
• hydroquinone silver metal
• The film is then treated with hypo a solution
  of sodium thiosulfate (Na2S2O3, an O is replaced
  by a S in Na2SO4) to remove the AgBr unexposed to
  get the negative
• Then, light will be pass through the negative
  to induce reaction on a light-sensitive paper to
  obtain the pictures.

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Chapter 8. (L31)-Oxidation and Reduction

• Antioxidants
• ..In food chemistry, certain reducing agents are
  called antioxidants.
• Example
• ascorbic acid (Vitamin C) is used to react with
  oxygen to avoid its reaction with food
• Browning of apples and pears oxidation of the
  fruit by oxygen
• Vitamins are considered to act as antioxidants
  in living systems for protection

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Chapter 8. (L31)-Oxidation and Reduction

• Redox chemistry living things
• ..Respiration
• C6H12O6 6O2 6CO2 6H2O energy
• C6(H2O)6 6O2 6CO2 6H2O energy
• ..Photosynthesis
• 6CO2 6H2O sunlight energy C6(H2O)6 6O2
• Source of oxygen on earth photosynthesis
• The old earth did not have oxygen in the air
  before photosynthesis bacteria came into being.

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Chapter 8. (L31)-Oxidation and Reduction

• Quiz Time
• Hydrogen is
• (a) a metal
• (b) the lightest and unique element
• (c) an oxidant
• (d) none no above is right.

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Chapter 8. (L31)-Oxidation and Reduction

• Quiz Time
• Which of the following reactions is the one for
  hydrogen fuel cell
• (a) Cr2O3 2Al 2Cr Al2O3
• (b) N2 3H2 2NH3
• (c) C O2 CO2
• (d) O2 2H2 2H2O.

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Chapter 8. (L31)-Oxidation and Reduction

• Quiz Time
• When a picture is taken, light causes which of
  the following to happen
• (a) damage of the film
• (b) drying of water in the film
• (c) reduction the Ag cation in the AgBr salt on
  the film to Ag particles
• (d) burning of the film.

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Chapter 8. (L31)-Oxidation and Reduction

• Quiz Time
• Which of the following is an antioxidant
• (a) water
• (b) baking soda
• (c) vinegar
• (d) Vitamin C.

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Chapter 8. (L31)-Oxidation and Reduction

• Quiz Time
• Vitamin C is a common name for
• (a) phosphoric acid
• (b) sulfuric acid
• (c) ascorbic acid
• (d) hydrochloric acid.

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Chapter 8. (L31)-Oxidation and Reduction

• Quiz Time
• Vitamin C is
• (a) an oxidant
• (b) non redox agent
• (c) a reductant
• (d) none of above is right.

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Chapter 8. (L31)-Oxidation and Reduction

• Quiz Time
• Which of the following reactions is
  photosynthesis
• (a) C2H4 H2 C2H6
• (b) O2 2H2 2H2O
• (c) C6(H2O)6 6O2 6CO2 6H2O energy
• (d) 6CO2 6H2O sunlight energy C6(H2O)6
  6O2.