1. Oxidation-Reduction Reactions
4.9
Oxidation-Reduction Reactions

2. Oxidation-Reduction Rxns. (Redox Rxns)
A chemical reaction where one or more electrons are transferred
Photosynthesis, combustion reactions, sugar/fat/protein oxidation in humans

3. Covalent Vs. Ionic Bonds
Covalent - electrons are shared
Between elements in molecular compounds (remember two nonmetals make binary molecular compounds???)
Ionic - opposite charges (cations and anions) are attracted like magnets (strong bond)

4. Oxidation States (oxidation numbers)
Helps show where electrons are transferred in chemical reactions…RULES…
Lone and diatomic elements = zero
Oxygen = -2 except in H2O2 (charge is -1)
In ionic compounds, ions’ #s are same as their charge
Do negative first. Charges add to make zero (or a charge if the compound is charged)
Ion charges: n+ or n- (#before charge)
Oxidation states: +n or -n (# after charge)

6. Try these… Fe3O4 This can happen (non whole number oxidation numbers)
O: -2 each, N: +2
PbS
S: -2, Pb: +2
SnCl6-2
Cl: -1 each, Sn: +4 H+
H: +1
Cl2
Cl: 0
Fe3O4
O: -2 each, Fe: +8/3
This can happen (non whole number oxidation numbers)

7. Purpose
In reactions, we want to know what elements gain or lose electrons
This is shown through assigning oxidation numbers
The element that becomes more negative gains electrons, decreases oxidation state (reduction)
The element that becomes more positive loses electrons, increases oxidation state (oxidation)
One doesn’t happen without the other.

8. Memorize!
LEO (lose electrons oxidation) the lion goes GER (gain electrons reduction)…or…
OIL (oxidation is lost) RIG (reduction is gained)
Example: CH4(g) + 2O2(g) --> CO2(g) + 2H2O(g)
Complete/balance equation if necessary
Assign oxidation states/numbers
Determine which element is oxidized/reduced

9. Also… C: -4 -> +4 so it’s oxidized O: 0 -> -2 so it’s reduced
Donates e- so REDUCING AGENT (allows something else to be oxidized)
O: 0 -> -2 so it’s reduced
Accepts e- so OXIDIZING AGENT (allows something else to be reduced)

10. You try… PbS(s) + O2(g) --> PbO(s) + SO2(g) Assign oxidation #s
S: oxidized, reducing agent
O: reduced, oxidizing agent
Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction?

11. Balancing Redox Rxns.
Fancy way of balancing skeleton equations using electrons
Two ways:
By oxidation states (LEARNING.)
Half-reactions (chapter 18)

12. Steps to follow 1. Assign oxidation states/numbers
2. Use lines to connect oxidation and reduction on both sides of the reaction
3. Add coefficients that will neutralize the number of electrons gained and lost
4. Balance the rest of the equation
5. Make sure your states of matter are appropriate

13. Example
Balance the reaction between solid lead(II)oxide and ammonia gas to produce nitrogen gas, liquid water, and solid lead.