1. Oxidation-reduction reactions
Pgs
Oxidation-reduction reactions

2. Oxidation-Reduction Reactions
Reactions that occur when electrons are transferred between atoms
Also called Redox Reactions
Oxidation = LOSS of electrons
Reduction = GAIN of electrons
LEO the lion goes GER

3. Oxidation – Reduction Reactions
Reaction of sodium metal with chlorine gas:
2Na (s) + Cl2 (g)  2NaCl (s)
What’s really happening in this reaction?
Na Cl
Na+Cl-
Metals ALWAYS lose electrons to nonmetals  metals = ox, nonmetals = reduced
Na+Cl-
Each sodium gives-up an electron to the chlorine resulting in ions!

4. Practice!!
In each of the following reactions, identify what is being oxidized, and what is being reduced?
2Mg (s) + O2 (g)  2MgO (s)
2Al (s) + 3I2 (s)  2AlI3 (s)

5. Can reactions between nonmetals be redox reactions?
Yes, but it’s harder to see
CH4 (g) + 2O2 (g)  CO2 (g) + H2O (g) + energy
Use oxidation states to determine where the electrons are going!

6. Oxidation States Also called oxidation numbers
Positive and negative numbers assigned to an INDIVIDUAL atom to help of keep track of electrons during redox reactions

7. Rules for Assigning Oxidation Numbers
Oxidation number of a free element = zero
Examples  HONClBrIF, solid metals (Na, Ag)
Oxidation number of a monatomic ion is the same as it’s charge
Examples  NaCl CaCl2
Oxygen’s oxidation number in compounds is -2, EXCEPT for peroxides where it is -1
Examples  O H2O H2O2

8. Rules for Assigning Oxidation Numbers
Hydrogen’s oxidation number = +1 in covalent compounds
Examples  H2O HI NH3
For a neutral compound, the sum of the oxidation states must be ZERO
Examples  CuCl2 Fe2O3
For polyatomic ions, the sum of the oxidation numbers must equal the charge of the ion
Examples  SO42-

9. Practice!! Assign oxidation numbers to each of the following atoms:
SO3 N2O5 C2H6
SO32- PF3

10. What do we use oxidation numbers for?
To determine what is being oxidized and what is being reduced in a redox reaction
Example:
Identify what is oxidized and reduced in the following reaction:
HINT  Oxidation = INCREASE in oxidation #
Reduction = DECREASE in oxidation #
CH4 (g) + 2O2 (g)  CO2 (g) + H2O (g)

11. Practice!!
Determine what is oxidized and reduced in the following reactions:
Cu (s) + 2AgNO3 (aq)  Cu(NO3)2 + 2Ag
Br2 (g) + 2NaF (aq)  2NaBr (aq) + F2 (g)
CH3OH (g) + O2 (g)  CO2 (g) + H2O (g)

12. Two more terms to know… Reducing Agent electron donor
What is oxidized in the reaction
Oxidizing Agent  electron acceptor
What is reduced in the reaction
Identify the reducing agent and oxidizing agent in the previous 3 reactions:
Cu (s) + 2AgNO3 (aq)  Cu(NO3)2 + 2Ag
Br2 (g) + 2NaF (aq)  2NaBr (aq) + F2 (g)
CH3OH (g) + O2 (g)  CO2 (g) + H2O (g)