1. Oxidation-Reduction Reactions
REDOX
Oxidation-Reduction Reactions

2. Oxidation-Reduction Reactions
Electrons are transferred from 1 atom to another.
All single-replacement & combustion rxns are redox rxns.

3. Oxidation
= loss of electrons.
LOSS of ELECTRONS = OXIDATION
LEO

4. Reduction
= gain of electrons.
GAIN of ELECTRONS = REDUCTION
GER

5. REDOX Oxidation & Reduction are complementary.
They occur together & simultaneously or not at all.

6. LEO GOES GER!!!
Memorize!
Oxidation of Cu

7. Oxidation Numbers
In Ionic Compounds: the number of electrons lost or gained by an atom when it forms ions.
Oxidation states of Vanadium

8. Assigning Oxidation Numbers
8 RULES

9. 8 Rules for Oxidation Numbers1.
of a free, uncombined element = 0.
Na He O2 N2 S8 Cl2 P 2.
of a monatomic ion = charge on ion.
Ca+2 = +2. Cl-1 = -1. Al+3 = +3.
Remember: Ions occur in ionic compounds: CaCl2, Al(NO3)3, etc.

10. 8 Rules for Oxidation Numbers3.
Fluorine is always -1.
CF4 4.
Hydrogen is nearly always +1, except when it’s bonded to a metal. Then it’s -1.
LiH CaH2 NaH
H2O, HNO3, H2SO4

11. 8 Rules for Oxidation Numbers5.
Oxygen is nearly always -2 except when its
-Bonded to fluorine, where O is +2
OF2
-In the peroxide ion, where O is -1.
O22-

12. 8 Rules for Oxidation Numbers6.
The sum of oxidation numbers in a neutral compound is 0.
H2O CO2 NO SO3 7.
The sum of oxidation numbers in a polyatomic ion = charge of the ion.
Sum in SO42- = -2. Sum in NO3- = -1.

13. 8 Rules for Oxidation Numbers8.
In covalent compounds, the oxidation number of the more electronegative atom is the negative charge it would have if it was an ion.
*NH3: N = -3, H = +1.
SiCl4: Si = +4, Cl = -1.

14. Assign Oxidation Nos KCl CaBr2 CO CO2 Al(NO3)3 Na3PO4 H2S NH4+1 SO3-2
Al = +3, O = -2, N = +5
Na = +1, O = -2, P = +5
H = +1, S = -2
N = -3, H = +1
S = +4, O = -2

15. Electrons are Negative!
Why do we use the word “reduced” when electrons are gained?
Look at how the oxidation number changes.
For example, if Cl gains an electron it becomes Cl-1. The oxidation number decreased from 0 to -1. The oxidation number was reduced.

16. Writing Equations
Even though oxidation & reduction occur together, we can write separate equations for each process.
Called Half-Reactions.
In order to balance a redox equation, we have to split the full equaton into half-reactions.

17. Conservation of Mass
# of atoms of each type is the same on both sides of the equation.
Still holds for half-reactions.
Do this step first.

18. Conservation of Charge
Total charge on LHS must equal total charge on RHS.
In the past, we usually had both sides neutral. (0 = 0.)
Note: Total charge can be nonzero. Just has to be equal on the 2 sides.
If not balanced, add electrons to whichever side is too positive.

19. Reduction Half-Reactions
Electrons are gained so they are like a reactant!
I e-  2I-
O e-  2O-2
Half-reactions must demonstrate conservation of mass & conservation of charge.
# of atoms of each element on LHS equals “ “ “ “ “ “ “ RHS.
Total charge on LHS = Total charge on RHS

20. Oxidation Half-reactions
K  K e-
Fe2+  Fe e-
Cu  Cu e-
Total Charge on LHS = Total Charge on RHS
# atoms LHS = # atoms RHS
Electrons are lost so they appear on the product side!

21. Identifying Half-Reactions
Reduction: electron term is on reactant side.
Oxidation: electron term is on product side.

22. Vocabulary Interlude
Oxidizing Agent: Is itself reduced. Accepts electrons from something else – aids oxidation for another species.
Reducing Agent: Is itself oxidized.
Loses electrons to something else – aids reduction for another species.

23. Figuring out what is what!
Given an unbalanced equation.
Goal: Balance it.
Procedure:
Assign oxidation numbers to everything
Split into half-reactions
Balance them separately
“Match” the electrons
Add them together

24. What’s oxidized & what’s reduced?
USE OIL RIG

25. 2) And if you’re lucky you strike oil & it shoots up4 3 2 1 -1 -2 -3 -4
2) And if you’re lucky you strike oil & it shoots up
OIL RIG
1) You dig down with an oil rig

26. Oxidizing & Reducing Agents
They are both ALWAYS on the reactant side.
Identify them by seeing how the oxidation numbers change.
Mg + Cu2+  Mg Cu 4 3 2 1 -1 -2 -3 -4 +2 +2
OIL RIG
Mg is oxidized, so
Mg is the reducing agent!

27. Oxidizing & Reducing Agents
What’s oxidized & what’s reduced:
Ca + FeCl2  CaCl2 + Fe
Assign oxidation numbers
Figure out what increases & what decreases.
+2, -1
+2, -1 4 3 2 1 -1 -2 -3 -4
OIL RIG
Ca is oxidized; Fe2+ is reduced.
Ca = reducing agent; FeCl2 = oxidizing agnt.

28. Oxidizing & Reducing Agents
2 FeBr3 + SnBr2  2 FeBr2 + SnBr4
Fe3+ is reduced to Fe2+
Sn2+ is oxidized to Sn4+
FeBr3 is the oxidizing agent.
SnBr2 is the reducing agent.
4, -1
3, -1
2, -1
2, -1