4Fe 3O2 2 Fe2O3

1

• 4Fe 3O2 ? 2 Fe2O3

2
Oxidation

• Loss of electrons by a substance.

3
Reduction

• Gain of electrons.

4

• 4 Fe ? 4 Fe3 12 e
• 3 O2 12 e ? 6 O2

5

• CuAgNO3?CuNO3Ag

Cu 2Ag? Cu22Ag Cu? Cu2 2 e
Ag e ? Ag
6
OIL RIG

• Oxidation Is Loss
• Reduction Is Gain
• of electrons

7
Oxidation-Reduction Reactions ( Redox)

• Chemical process of elements undergoing a change
  in oxidation number.

8

• I2 2 e ? 2 I
• K ? K e
• Fe2 ? Fe3 e
• Ag e ? Ag

9
Oxidizing Agent

• causes the oxidation of another substance by
  accepting electrons from that substance.

10
Reducing Agent

• causes the reduction of another substance by
  providing electrons.

11

• 2Br Cl2? Br2 2Cl
• 2 Zn O2? 2 ZnO

12

• Mg I2? MgI2
• H2S Cl2? S 2HCl

13
Oxidation Number

• a number assigned to an element in a molecule to
  show the distribution of electrons.

14
Determining Oxidation numbers 1

• The oxidation number of an uncombined atom zero.

15
2

• The oxidation number of a monatomic ion is its
  ionic charge.

16
3

• Many oxidation numbers correspond to
  electronegativity.
• (periodic table position)

17
3 combined elements

• F -1
• Group 1A 1
• H 1 (-1 when combined with a metal)
• Group 2A 2
• Al 3
• O -2 (usually)
• halogens usually -1

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4

• The sum of oxidation numbers of atoms in a
  compound must equal its charge.

19
Fe Cu2 ? Fe2 Cu 0 2
2 0

• Ionic charge x, x-
• Oxidation x, -x

20
Problem

• Find the oxidation numbers for each element in
  K2SO4.

21
Problem

• Find the oxidation numbers for each element in
  Cr2O72-

22
Problem

• NH4
• AsO43-
• CrO42-

• NaClO4
• AlPO4
• HNO2