1. Chapter 19
Redox Reactions

2. Oxidation Numbers Rules Examples Uncombined element = 0
Monatomic ion = charge on ion (from location of periodic table)
2 element compound – right gets what it wants (from periodic table), calculate left
3 element compound – right and left get what they want, calculate middle
Examples

3. Oxidation-Reduction (Redox)
Loss of e- (becomes more positive)
Reduction
Gain of e- (becomes more negative)
LEO the lion says GER
Loss of e- is oxidation
Gain of e- is reduction
Example

4. Recognizing Redox Reactions
THERE HAS TO BE A CHANGE IN OXIDATION NUMBER FOR A REACTION TO BE REDOX!!
Examples

5. Half-Reactions
Separate redox reaction into the individual oxidation and reduction reactions
Examples

6. Redox Reactions Oxidizing Agent Reducing Agent
Substance that causes oxidation
It is Reduced!
Reducing Agent
Substance that causes reduction
It is Oxidized!

7. Balancing Half-Reactions
Steps:
Write half-reactions separately
Balance everything except H and O
Balance O by adding water
Balance H by adding H+
Balance overall charge by adding e-’s
Add oxidation and reduction reactions with equal e-’s
Cancel if possible

8. Balancing Half-Reactions
Examples

9. Electrochemistry Using half-reactions and calculating voltages Anode
Site of oxidation
Lower reduction potential
Cathode
Site of reduction
Ecell = Ecathode – Eanode

10. Electrochemistry Examples
Cr+3+/Cr with Zn+2/Zn – Use chart on page 615

11. Calculating Voltage for a Cell
Zn2+/Zn with Cu2+/Cu
What two half reactions will occur?
What is the oxidation half reaction?
What is the reduction half reaction?
What would the voltage reading be for the entire cell?
Which electrode would get bigger?
Which electrode would be consumed?

12. Calculating Voltage for a Cell