1. Oxidation and Reduction
Section 9.1

2. Electron Transfer Theory
According to modern theory
the gain of electrons is called reduction.
the loss of electrons is called oxidation.
In metallurgy reduction = producing metals from ore and oxidation = reaction with oxygen (combustion, corrosion)
LEO the lion says GER

3. Redox Theory suggests:
the total number of e- gained in a reaction must equal the total number of e- lost
Reduction and oxidation are separate processes that occur simultaneously
The chemical equations of the oxidation, reduction and the overall equation must be balanced.

4. Writing and Balancing Half-Reactions
Write a balanced net equation for the reaction of copper with aqueous silver nitrate.
Step 1: Write each half reaction (the metal reacting with the solution will undergo an oxidation – forms a + ion thus a loss of electrons, while the one in solution will undergo a reduction)

5. Example Continued…
Step 2: Remember the number of electrons lost must equal the number of electrons gained. So we need to multiply the second reaction by two so that we will have 2e- in each equation

6. Example Cont… Step 3: Now add the two half-reaction equations
Step 4: Cancel out like terms
Step 5: Write net equation

7. Oxidation States
An oxidation number is a positive or negative number corresponding to the oxidation state of an atom
Using the following rules you can determine the oxidation number of other atoms in compounds (pg. 658)
Oxidation # are assigned arbitrarily, they are not electric charges. The pos/neg sign comes before the number

8. Examples
What is the oxidation number of sodium in sodium hydride (NaH)?
- hydrogen in a hydride has an oxidation # of -1
- b/c there is only 1 Na, it must be +1
What is the oxidation number of sulphur in dihydrogen sulphide (H2S)?
- hydrogen is always +1
- b/c there are 2 of them the overall is 2(+1) = +2
- b/c only 1 S, it must be -2

9. Examples Cont…
What is the oxidation number of carbon in the carbonate ion (CO22-)?
- O has an oxidation number of -2
- there is an overall charge of 2- on the ion so we can set up a mini equation:
- solve for x

10. Examples Cont…
What is the oxidation number of sulphur in calcium sulphate ( )
We can assumed that Ca is in ionic form  its oxidation number is +2
So we can set up our equation and solve

11. Oxidation Numbers and Redox Reactions
An oxidation is an increase in oxidation number
A reduction is a decrease in oxidation number
In redox reactions, oxidation numbers change.

12. Example:
When methane burns, carbon dioxide and water form. Identify the oxidation and reduction in this reaction:
First write the reaction:
Now insert the oxidation numbers and arrows:

13. Seatwork:
Pg. 653 #2
Pg. 656 #8-9
Pg. 659 #12, 13
Pg. 662 #18, 19, 20