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Ch. 5 Oxidation and Reduction. Milbank High School . Ch. 5 Objectives. Define some important properties of oxygen List important properties of hydrogen Describe oxidation and reduction Identify an oxidation/reduction reaction Identify some common oxidizing and reducing agents

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ch 5 oxidation and reduction

Ch. 5Oxidation and Reduction

Milbank High School

ch 5 objectives
Ch. 5 Objectives
  • Define some important properties of oxygen
  • List important properties of hydrogen
  • Describe oxidation and reduction
  • Identify an oxidation/reduction reaction
  • Identify some common oxidizing and reducing agents
  • List some of the important oxidization and reduction reactions involving living organisms
overview
Overview
  • Oxidation and reduction reactions always occur together (redox reactions)
  • You can’t have one without the other
  • Includes: extracting metal from an ore
  • Salt on roads
    • Salt accelerates the reaction between oxygen and metal
    • Makes electron transfer easier
oxygen
Oxygen
  • Most abundant element on Earth
  • 21% of our atmosphere (pure)
  • 89% of Earth’s water (compound)
  • 45.5% of Earth’s crust (compound)
  • 2/3rd’s of the human body (compound)
  • Foods (compound)
  • Rust
chemical properties of oxygen
Chemical Properties of Oxygen
  • Combines with many elements and compounds
  • Rust (reacts with metals)
  • Other oxides (reacts with nonmetals)
  • Methane (reacts with other compounds)
    • Bunsen burner
hydrogen
Hydrogen
  • In the universe, 95% of all atoms are hydrogen
  • Seldom found alone
  • Hydrocarbons
  • Hindenburg…
3 ways of looking at oxidation and reduction
3 ways of looking at oxidation and reduction
  • 1. oxidation is a gain of oxygen atoms, reduction is a loss of oxygen atoms
  • 2. oxidation is a loss of hydrogen atoms, reduction is a gain of hydrogen atoms
  • 3. oxidation is a loss of electrons, reduction is a gain of electrons
    • Most fundamental explanation, what we will be dealing with the most
slide8

Oxygen

Hydrogen

e-

in relation to our lab
In relation to our lab…
  • Remember that reduction is a loss of oxygen from a compound
  • We converted iron ore to metallic iron
    • We removed oxygen from the iron(III) oxide
    • 2Fe2O3 + 3C  4Fe + 3CO2
    • Carbon was oxidized because it gained an oxygen
leo the lion
Leo the Lion!
  • LEO the lion says GER
    • Loss of electrons is oxidation, gain of electrons is reduction
examples
Examples
  • Is the reactant oxidized or reduced?
  • Pb  PbO3
  • SnO2  SnO
  • KClO3 KCl
  • C2H6O  C2H4O
  • C2H2  C2H6
pertaining to leo
Pertaining to LEO…
  • Mg + S  MgS
  • Mg + S  Mg2+ + S2-
  • Magnesium is oxidized
    • Said to be the reducing agent
    • Substance in the reaction that loses electrons
  • Sulfide sulfur atom is reduced
    • Said to be the oxidizing agent
    • Substance in the reaction that gains electrons
oxidation numbers
Oxidation Numbers
  • A count of the electrons transferred or shared in the formation or breaking of chemical bonds
  • You must assign each element in the reaction an oxidation number
  • Follow a set of rules…
oxidation number rules
Oxidation Number Rules

1. The total of the oxidation numbers of all the atoms in a neutral molecule, an isolated atom, or a formula unit is 0

  • Examples

2. In their compounds, the Group 1A metals all have an oxidation number of +1, and the Group 2A metals have an oxidation number of 2+.

  • Examples
rules con t
Rules Con’t

3. In its compounds, hydrogen has an oxidation number of +1 (except in metal hydrides such as NaH, where it is -1)

  • Examples

4. In its compounds, oxygen has an oxidation number of -2 (except in peroxides such as H2O2, where it is -1)

  • Examples

5. In their binary compounds with metals, Group7A elements have an oxidation number of -1. Group 6A elements have an oxidation number of -2, and Groups 5A elements have an oxidation number of -3.

  • Examples
problems
Problems
  • What is the oxidation number of each element?
  • I2
  • Cr2O3
  • AlCl3
  • Na2SO4
  • CaH2
identifying redox reactions
Identifying Redox Reactions

0 +3 -2 0 +3 -2

  • 2 Al + Fe2O3 2 Fe + Al2O3
  • Al increases from 0 to +3, it is ______
  • Oxidized!
  • Fe decreases from +3 to 0, it is _______
  • Reduced!
problems1
Problems
  • Zn  Zn2+
  • Fe3+  Fe2+
  • CaCO3  CaO + CO2
  • AgNO3  Ag
  • Do Practice Exercises
oxidizing and reducing agents
Oxidizing and Reducing Agents
  • Now the confusing part…
  • CuO + H2 Cu + H2O
  • Cu goes from +2 to 0
    • Cu is reduced, therefore it is called an oxidizing agent because it causes some other substance to be oxidized
  • H goes from 0 to +1
    • H is oxidized, therefore it is called a reducing agent because it causes some other substance to be reduced.
identifying agents in an equation
Identifying Agents in an Equation
  • CuO + H2 Cu + H2O

Reduction: CuO is the oxidizing agent

Oxidation: H2 is the reducing agent

some common oxidizing agents
Some common oxidizing agents
  • Oxygen!
    • Oxidized coal in electric power
    • Gas in automobiles
    • Wood in campfires
    • Food we eat
  • Antiseptics
    • Hydrogen Peroxide
    • Benzoyl peroxide
  • Disinfectants
    • Chlorine
some common reducing agents
Some common reducing agents
  • Metals
  • Antioxidants
    • Ascorbic acid is used to prevent the browning of fruits by inhibiting air oxidation
    • Many antioxidants are believed to retard various oxidation reactions that are potentially damaging to vital components of living cells
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