1. Oxidation, Reduction and Electrochemistry
In this chapter you will be exposed to some basic concepts involved in a special type of chemical reaction.
Time will not permit an in-depth study of this, but the main concepts will be important to learn.

2. Oxidation-Reduction Reactions
Oxidation-Reduction reactions are also termed Redox reactions.
A redox reaction is a chemical reaction which involves the loss and gain of electrons.

3. Redox Reactions
In a redox reaction one substance is oxidized (loses electrons) and another substance is reduced (gains electrons)
OIL RIG ( oxidation is loss, reduction is gain of electrons)
LEO the lion goes GER (loss of electrons is oxidation, gain of electrons is reduction.
2 Na(s) + Cl2(g) NaCl
Na – loses 1 electron (oxidized)
Cl – gains 1 electron (reduced)

4. Practice Problem
Identify the substance oxidized and reduced in the following redox equation.
Ag (s) + NO3 (aq) AgNO3

5. Oxidation Numbers
To analyze an equation as a redox reaction it’s essential to identify the oxidation numbers of the reactants and products.
Changes in oxidation numbers reveal if a substance is oxidized or reduced.

6. Oxidation Number Rules
When assigning oxidation numbers use the following rules:
The oxidation number for any “free” or uncombined element in atomic or molecular form is 0.
The oxidation number of a monatomic ion is equal to the charge on the ion.
The oxidation number of an atom of fluorine in a compound is always –1 because it is the most electronegative.

7. Oxidation Numbers
4) An atom of the more electronegative element in a binary compound is assigned the number equal to its ion charge.
In compounds, atoms of group I, II, and aluminum have positive oxidation numbers : +1, +2, +3 respectively.
Hydrogen is +1 unless combined with a metal atom, then its –1.
The oxidation number of oxygen is usually –2. When combined with fluorine it is +2. In peroxides, such as H2O2 oxygen has the oxidation number –1.

8. Oxidation Numbers
8) The sum of the oxidation numbers of all atoms in a particle must equal to zero in a compound and to its charge for a polyatomic ion.

9. Oxidation Number Practice
NH4+ :
Al :
BF3 :
KClO3
CO32-

10. Oxidation Number Practice
NH4+ : H= N= -3
Al : 0
BF3 : F= B: +3
KClO K= O= Cl= +5
CO O= C=+4

11. Identifying Redox Reactions
To identify a redox reaction you must analyze the oxidation numbers of reactants and products.
Redox Reaction

12. Identify oxidized and reduced substance:
1) Cl2 + 2HBr  2HCl + Br2 +1 -1 +1 -1
Assign oxidation numbers to each atom in the equation.
Consider only the atoms for which there was a change in oxidation number.

13. Identify oxidized and reduced substance:
1) Cl2 + 2HBr  2HCl + Br2 +1 -1 +1 -1
An increase in oxidation number indicates an oxidation.
A decrease in oxidation number indicates a reduction.
The oxidation number of Cl decreased (from 0 to -1): Cl was reduced
The oxidation number of Br increased (from -1 to 0): Br was oxidized

14. Identify oxidized and reduced substance:
2) 2H2 + O2  2H2O +1 -2
An increase in oxidation number indicates an oxidation.
A decrease in oxidation number indicates a reduction.
The oxidation number of O decreased (from 0 to -2): O was reduced
The oxidation number of H increased (from 0 to +1): H was oxidized

15. Classwork
Oxidizing and reducing handout