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Chapter 6, Activity 8. “Oxidation-Reduction Reactions”. LEO SAYS GER. Activity 8 The Meaning of Oxidation and Reduction (called “ redox ”). OBJECTIVES Define oxidation and reduction in terms of the loss or gain of oxygen, and the loss or gain of electrons.

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chapter 6 activity 8

Chapter 6, Activity 8

“Oxidation-Reduction Reactions”

LEO SAYS GER

activity 8 the meaning of oxidation and reduction called redox
Activity 8The Meaning of Oxidation and Reduction (called “redox”)
  • OBJECTIVES
    • Define oxidation and reduction in terms of the loss or gain of oxygen, and the loss or gain of electrons.
activity 8 the meaning of oxidation and reduction redox
Activity 8The Meaning of Oxidation and Reduction (Redox)
  • OBJECTIVES
    • State the characteristics of a redox reaction and identify the oxidizing agent and reducing agent.
activity 8 the meaning of oxidation and reduction redox1
Activity 8The Meaning of Oxidation and Reduction (Redox)
  • OBJECTIVES
    • Describe what happens to iron and other metals when they corrode.
oxidation and reduction redox
Oxidation and Reduction (Redox)
  • Early chemists saw “oxidation” reactions only as the combination of a material with oxygen to produce an oxide.
    • For example, when methane burns in air, it oxidizes and forms oxides of carbon and hydrogen
oxidation and reduction redox1
Oxidation and Reduction (Redox)
  • But, not all oxidation processes that use oxygen involve burning:
    • Elemental iron slowly oxidizes to compounds such as iron (III) oxide, commonly called “rust”
    • Hydrogen peroxide also releases oxygen when it decomposes
oxidation and reduction redox2
Oxidation and Reduction (Redox)
  • A process called “reduction” is the opposite of oxidation, and originally meant the loss of oxygen from a compound
  • Oxidation and reduction always occur simultaneously
  • The substance gaining oxygen (or losing electrons) is oxidized, while the substance losing oxygen (or gaining electrons) is reduced.
memory aids
MEMORY AIDS
  • LEO the lion goes GER
    • Loss of electrons is oxidation
    • Gain of electrons is reduction
  • OIL RIG
    • Oxidation is loss
    • Reduction is gain
oxidation and reduction redox3
Oxidation and Reduction (Redox)

Each sodium atom loses one electron:

Each chlorine atom gains one electron:

leo says ger
LEO says GER :

Lose Electrons = Oxidation

Sodium is oxidized

Gain Electrons = Reduction

Chlorine is reduced

leo says ger1
LEO says GER :

- Losing electrons is oxidation, and the substance that loses the electrons is called the reducing agent.

- Gaining electrons is reduction, and the substance that gains the electrons is called the oxidizing agent.

Mg(s) + S(s) → MgS(s)

Mg is oxidized: loses e-, becomes a Mg2+ ion

Mg is the reducing agent

S is the oxidizing agent

S is reduced: gains e- = S2- ion

not all reactions are redox reactions
Not All Reactions are Redox Reactions

- Reactions in which there has been no change in oxidation number are NOT redox reactions.

Examples:

corrosion
Corrosion
  • Damage done to metal is costly to prevent and repair
  • Iron, a common construction metal often used in forming steel alloys, corrodes by being oxidized to ions of iron by oxygen.
    • This corrosion is even faster in the presence of salts and acids, because these materials make electrically conductive solutions that make electron transfer easy
corrosion1
Corrosion
  • Luckily, not all metals corrode easily
    • Gold and platinum are called noble metals because they are resistant to losing their electrons by corrosion
    • Other metals may lose their electrons easily, but are protected from corrosion by the oxide coating on their surface, such as aluminum
    • Iron has an oxide coating, but it is not tightly packed, so water and air can penetrate it easily
corrosion2
Corrosion
  • Serious problems can result if bridges, storage tanks, or hulls of ships corrode
    • Can be prevented by a coating of oil, paint, plastic, or another metal
    • If this surface is scratched or worn away, the protection is lost
  • Other methods of prevention involve the “sacrifice” of one metal to save the second
    • Magnesium, chromium, or even zinc (called galvanized) coatings can be applied
trends in oxidation and reduction
Trends in Oxidation and Reduction
  • Active metals:
          • Lose electrons easily
          • Are easily oxidized
          • Are strong reducing agents
  • Active nonmetals:
          • Gain electrons easily
          • Are easily reduced
          • Are strong oxidizing agents
identifying redox equations
Identifying Redox Equations
  • In general, all chemical reactions can be assigned to one of two classes:
    • oxidation-reduction, in which electrons are transferred:
      • Single-replacement, synthesis, decomposition, and combustion
    • this second class has no electron transfer, and includes all others:
      • Double-replacement and acid-base reactions