Ch 5 oxidation and reduction
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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

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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


Ch 5 oxidation and reduction

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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