1. Oxidation - Reduction
RedOx

2. RedOx reactions
Chemical reactions involving an electron transfer between atoms. Elements will change oxidation state from the reactant side to the product side.

3. Rules of assigning oxidation states
If in doubt with + or - The higher e-neg will get the - !
Group 1 is +1
Group 2 is +2
Transition METALS are always positive!
Fluorine is -1
H is +1 in covalent & -1 in binary ionic
O is -2 except with F then O is +2, or in a peroxide then -1.

4. Cu(s) Zn(s) Cl2(g) O2(g) O3(g) C60(s) Ne(g)
…and
Elements that are not bonded to a different element have oxidation states of zero.
Examples
Cu(s) Zn(s) Cl2(g) O2(g) O3(g) C60(s) Ne(g)

5. H2S H2SO3 H2SO4 NOW More complicated . . .
sulfur has a -2 oxidation state
H2SO3
sulfur has a +4 oxidation state
H2SO4
sulfur has a +6 oxidation state
How? 

6. Assigning oxidation states to atoms in a polyatomic ion
Oxidation states on individual atoms must equal the charge on the ion
(S+6 O4-2 ) -8 +6
= -2
(S O4-2 ) -8
= -2
(S O4)
= -2
(SO4)

7. Try these . . .
hydroxide
ammonium
chromate

8. Try these answers. . . Hydroxide OH-1 O: -2 H: +1
ammonium NH N: -3 (b/c higher e-neg) H: +1
Chromate CrO Cr: +6 O: -2

9. Put it all together……. Assign oxidation states to each atom in the compound
KClO3
MnCr2O7
K2PtCl6

10. Put it all together……. answers
KClO3 K: +1 Cl: +5 O: -2
MnCr2O7 Mn: +2 Cr: +6 O:-2
K2PtCl6 K: +1 Pt: +4 Cl: -1

11. 2Na + 2HOH 2NaOH + H2 Hydroxide polyatomic ion Recognizing RedOx
If the oxidation state changes for any of the atoms it is considered a RedOx reaction
2Na + 2HOH NaOH + H2
Hydroxide polyatomic ion

12. Single Replacement Reactions are ALWAYS RedOX
Double Replacement Reactions are NEVER RedOX

13. RedOx: Yes or NO? HCl + NaOH  HOH + NaCl Mg + 2HCl  MgCl2 + H2
MnO2 + 4HBr MnBr2 + Br2 + 2H2O

14. RedOx
Definitions….

15. Metals tend to undergo oxidation+3 +2 +1 -1 -2 -3
Oxidation results in an increase in oxidation state
Atoms that Lose e-lectrons undergo Oxidation
Metals tend to undergo oxidation

16. Non-metals tend to undergo reduction+3 +2 +1 -1 -2 -3
Reduction results in a decrease in oxidation state
Atoms which Gain e-lectrons undergo Reduction
Non-metals tend to undergo reduction

17. GeR

18. oxidation and reduction
In a RedOx reaction
If one atom is being oxidized another must be reduced.
In other words . . .
oxidation and reduction
always occur together

20. Assign oxidation states to each atom. Is this a RedOx reaction?
Al + CuCl2 Cu + AlCl3
Assign oxidation states to each atom.
Is this a RedOx reaction?
What species is oxidized?
Reduced?
Write a balanced equation based on these reactants.

21. 2Al + 3CuCl2  2AlCl3 + 3Cu
Write a balanced equation based on these reactants.
Is this a RedOx reaction? YES
What species is oxidized? Al0
Reduced? Cu+2

22. Assign oxidation states to all atoms What species is oxidized?
MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O
Assign oxidation states to all atoms
What species is oxidized?
How do you know?
What species is reduced?

23. Oxidation state increases from -1 to 0 Cl-1 loses electrons
MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O
What species is oxidized? Cl -1
How do you know?
Oxidation state increases from -1 to 0
Cl-1 loses electrons
What species is reduced? Mn+4
Oxidation state decreases from +4 to +2
Mn+4 loses electrons

24. RedOx Practice Losing e- oxidation Gain e- Reduction Remember . . . +4+3 +2 +1 -1 -2 -3 -4
Losing e- oxidation
Gain e- Reduction
Remember . . .

25. Writing half-reactions
A half reaction shows either oxidation or reduction of a RedOx reaction.
The electrons being lost (oxidation) or gained (reduction) are also shown.

26. Oxidation half-reaction example
Fe(s)  Fe+3(aq) + 3e-
Fe0 gets oxidized
electrons are lost
products
conservation of mass AND CHARGE
charges on both sides equal each other

27. Reduction half-reaction example
Sn+4 + 2e-  Sn+2
Sn+4 gets reduced
electrons are gained
reactants
conservation of mass AND CHARGE
charges on both sides equal each other

28. Practice KMnO4 + HCl  MnCl2 + KCl + Cl2 + H2O
Assign oxidation states….
What species is oxidized?
½ rxn?
What species is reduced?
Where does the electron transfer take place?

29. Answers KMnO4 + HCl  MnCl2 + KCl + Cl2 + H2O
What species is oxidized? Cl-1
½ rxn? Cl-1  Cl0 + 1e- or 2Cl-  Cl20 + 2e-
What species is reduced? Mn+7
½ rxn? Mn+7 + 3e-  Mn+4
Where does the electron transfer take place? Cl- loses e- to Mn+7

30. The End
I came I saw I RedOxed