1. Unit 7: Redox &
Electrochemistry

2. What information does the oxidation number give you?
Bell Ringer
What information does the oxidation number give you?

3. Why electrochemistry? REDOX reactions are important in …
30/09/99
Why electrochemistry?
REDOX reactions are important in …
Purifying metals (e.g. Al, Na, Li)
C3H8O + CrO3 + H2SO4  Cr2(SO4)3 + C3H6O + H2O
Producing gases (e.g. Cl2, O2, H2)
Electroplating metals
Electrical production (batteries, fuel cells)
Protecting metals from corrosion
Balancing complex chemical equations
Sensors and machines (e.g. pH meter)

4. Remember: LEO the lions says GERRRRRR!
What is Redox?
30/09/99
REDOX stands for REDuction/OXidation
Oxidation is often thought of as a combination of a substance with oxygen (rusting, burning)
Oxidation refers to a loss of e-
Reduction refers to a gain of e-
Remember: LEO the lions says GERRRRRR!
Loss Electrons = Oxidation
Gain Electrons = Reduction

5. Reactions Fe  Fe+3 +3e- What is happening to the Fe atom?
Fe is going from 0 to +3 oxidation #
It must be losing electrons
Loss of Electrons = Oxidation
In conclusion, the iron atom is being oxidized

6. In conclusion, the sulfur atom is being reduced
Reactions
S +2e-  S-2
What is happening to the Sulfur atom?
S is going from 0 to -2 oxidation #
It must be gaining electrons
Gain of Electrons = Reduction
In conclusion, the sulfur atom is being reduced

7. Oxidation Numbers 1. FREE ELEMENTS Na  Na0 H2  H20 F2  F20
- the charge an atom would have if the electrons belonged to the more EN atom
- there are a few rules to help us out
1. FREE ELEMENTS
Always have an oxidation number of zero Na 
Na0 H2 
H20 F2 
F20

8. H is ALWAYS +1 (for us) Oxidation Numbers 4. HYDROGEN
- the charge an atom would have if the electrons belonged to the more EN atom
4. HYDROGEN
H is ALWAYS +1 (for us)
Disclaimer – there are compounds where H has a -1 oxidation number, but we don’t deal with them at this level of chemistry.

9. O is ALWAYS -2 (for us) Oxidation Numbers 5. OXYGEN
- the charge an atom would have if the electrons belonged to the more EN atom
5. OXYGEN
O is ALWAYS -2 (for us)

10. Oxidation Numbers 2. SIMPLE IONS Sodium ion  Na+1 Calcium ion  Ca+2
- the charge an atom would have if the electrons belonged to the more EN atom
2. SIMPLE IONS
Oxidation Number = the charge an ion would make
Sodium ion 
Na+1
Calcium ion 
Ca+2
Sulfur ion 
S-2
Nitrogen ion 
N-3

11. Oxidation Numbers 3. COMPOUNDS NaCl  Na+1Cl-1  As+5I5-1 AsI5 
- the charge an atom would have if the electrons belonged to the more EN atom
3. COMPOUNDS
The sum of all oxidation numbers will equal ZERO
NaCl 
Na+1Cl-1 
As+5I5-1
AsI5 
Cu+2(N+5O3-2)2
Cu(NO3)2 
H2+1Cr2+6 O7-2
H2Cr2O7

12. Oxidation Numbers 5. POLYATOMIC IONS (SO4)-2  (S+6O4-2)-2 
- the charge an atom would have if the electrons belonged to the more EN atom
5. POLYATOMIC IONS
The sum of oxidation numbers will equal the charge of that ion
(SO4)-2 
(S+6O4-2)-2 
(N+5O3-2)-
(NO3)- 
(Cr2+3O4)-2
(Cr2O4)-2

13. Do the five problems on your notes sheet
Oxidation Numbers
Do the five problems on your notes sheet
a. Cr2O3
d. KCl
b. H2Cr2O7
e. Mg(OH)2
c. AsCl5

14. What things are conserved during a chemical reaction?
Bell Ringer
What things are conserved during a chemical reaction?

15. What is reduced/oxidized?
Identify in the following reactions what is oxidized and what is reduced
2K + Cl2  2KCl
K0 – goes from 0 to +1, it is oxidized
Cl0 – goes from 0 to -1, it is reduced

16. Practice Cl-1 – goes from -1 to 0, it is oxidized
Identify in the following reactions what is oxidized and what is reduced
2NaCl + 3SO3  Cl2 + SO2 + Na2S2O7
Cl-1 – goes from -1 to 0, it is oxidized
S+6 – goes from +6 to +4, it is reduced

17. Practice Zn + Pb+2(aq)  Zn+2(aq) + Pb
Identify in the following reactions what is oxidized and what is reduced
Zn + Pb+2(aq)  Zn+2(aq) + Pb
Zn0 – goes from 0 to +2, it is oxidized
Pb+2 – goes from +2 to 0, it is reduced

18. Notes Sheet Practice ID Oxdized and Reduced
a. C + H2SO4  CO2 + SO2 + H2O
b. HNO3 + HI  NO + I2 + H2O
c. KMnO4 + HCl  MnCl2 + Cl2 + H2O + KCl
d. Sb + HNO3  Sb2O5 + NO + H2O
e. HCl + MnO2  MnCl2 + H2O + Cl2

19. Notes Sheet Practice a. C + H2SO4  CO2 + SO2 + H2O
b. HNO3 + HI  NO + I2 + H2O
c. KMnO4 + HCl  MnCl2 + Cl2 + H2O + KCl
d. Sb + HNO3  Sb2O5 + NO + H2O
e. HCl + MnO2  MnCl2 + H2O + Cl2

20. Notes Sheet Practice 1. C + 2Cl2  CCl4 Ox – Red – 2. H2 + Cl2  2HCl
3. 2P Cl2  2PCl3
4. C H2O  CO H2
5. Fe Cl2  2FeCl2

21. Notes Sheet Practice 6. 2Al + 3Br2  2AlBr3 Ox – Red –
7. Pb HCl  PbCl H2
8. SiO C  Si CO
9. CO Mg  2MgO C
10. H2SO Zn  ZnSO H2
Red -

22. Identify what atom is oxidized and what atom is reduced:
Bell Ringer
Identify what atom is oxidized and what atom is reduced:
Fe + 2HCl  FeCl2 + H2

23. Shows only one half of the reaction, including the e- lost or gained
HALF REACTIONS
Shows only one half of the reaction, including the e- lost or gained
Reduction:
Fe e-  Fe
-notice that there is a conservation of charge and mass
Oxidation:
Fe  Fe e- OR
Fe - 3e-  Fe3+

24. Write both half reactions for the following reaction:
Cu + AgNO3  Cu(NO3)2 + Ag
Reduction:
Ag+  Ag
Ag e-  Ag
Oxidation:
Cu  Cu+2
Cu  Cu e-
Cu - 2e-  Cu+2

25. Write both half reactions for the following reaction:
HNO3 + I2  HIO3 + NO2
Reduction:
N+5  N+4
N e-  N+4
Oxidation:
I20  I+5
I20  2I e-
I e-  2I+5

26. Write both half reactions for the following reaction:
30/09/99
Half Reactions
Write both half reactions for the following reaction:
Sn + AgNO3  Sn(NO3)2 + Ag
Reduction:
Ag+1  Ag0
Ag e-  Ag0
Oxidation:
Sn0  Sn+2
Sn0  Sn e-
Sn0 - 2e-  Sn+2

27. Aluminum and Copper Chloride Lab

28. Redox Lab
Al CuCl2  2 3
Cu AlCl3
Mass
GFM
Moles

30. Bell Ringer
If you were to react Cu and Nickel(II) Chloride what would the products be? How much metal could you make if you started with 2.00g of Cu?

31. Oxidizing and Reducing Agents
Oxidizing Agent 
- causes the oxidation of another atom
- it is actually the atom that is REDUCED
- oxidation number decreases
- causes the reduction of another atom
Reducing Agent 
- it is actually the atom that is OXIDIZED
- oxidation number increases
Ca + Cl2  CaCl2
What is the O.A.?
 Cl
What is the R.A.?
 Ca

32. PRACTICE 4HCl + MnO2  MnCl2 + 2H2O + Cl2 Oxidized:  Cl- Reduced:
In the equation below, identify what is oxidized what is reduced. Also identify the oxidizing and reducing agent.
4HCl + MnO2  MnCl2 + 2H2O + Cl2
Oxidized:
 Cl-
Reduced:
 Mn+4
Oxidizing Agent:
 Mn+4
Reducing Agent:
 Cl-

33. Electrochemical Reactions
Deals with chemical reactions that either produce electricity or need electricity to occur!
There are 2 types of ELECTROCHEMICAL CELLS.
Some things that are the same for both types of cells:
1. The RED CAT GETS FAT!
Anorexic Ox
2. Electrons always flow from the anode to the cathode!

34. Cell Type #1 - Voltaic Cell
Half Reactions
Cell Type #1 - Voltaic Cell
2e-
2e-
2e-
2e-
2e-
2e-
2e-
2e-
2e- Zn
Zn electrode
2e- Cu
Cu electrode
2e-
Lose e- (Table J)
Gains e- (Table J)
Oxidized
Reduced
Cu+2
Zn+2
Anode (-)
Cathode(+)
Cu+2
Zn+2
ZnSO4
CuSO4
Will this go on forever?

35. Cell Type #1 - Voltaic Cell
Half Reactions
Cell Type #1 - Voltaic Cell Zn
Zn electrode Cu
Cu electrode
Lose e- (Table J)
Gains e- (Table J)
Oxidized
Reduced
Anode (-)
Cathode(+)
Zn+2
ZnSO4
CuSO4
Will this go on forever?

36. Electrochemistry Cell Type #1 - Voltaic Cell Zn electrode gets smallerCu
Cu electrode Zn
Zn electrode
Lose e- (Table J)
Oxidized
Anode (-)
Gains e- (Table J)
Reduced
Cathode(+)
Cl-
Na+
2e-
Na+
Cl-
2e-
Cl-
Cl-
Na+
Na+
Zn+2
Cu+2
Na+
Cl-
Cl-
Na+
2Na+
Zn+2
2Cl-
Cu+2
ZnSO4
CuSO4
Zn electrode gets smaller
Cu electrode gets bigger

37. Cell Type #1 - Voltaic Cell
Half Reactions
Cell Type #1 - Voltaic Cell

38. 30/09/99
Bell Ringer
In the reaction below, identify what is the oxidizing agent and the reducing agent.
Ca + H2O  CaO + H2

39. Electrochemistry Cell Type #1 - Voltaic Cell Zn electrode gets smallerCu
Cu electrode Zn
Zn electrode
Lose e- (Table J)
Oxidized
Anode (-)
Gains e- (Table J)
Reduced
Cathode(+)
Cl-
Na+
2e-
Na+
Cl-
2e-
Cl-
Cl-
Na+
Na+
Zn+2
Cu+2
Na+
Cl-
Cl-
Na+
2Na+
Zn+2
2Cl-
Cu+2
ZnSO4
CuSO4
Zn electrode gets smaller
Cu electrode gets bigger

40. Cell Type #1 - Voltaic Cell
Electrochemistry
Cell Type #1 - Voltaic Cell
Summary:
Voltaic Cells – are spontaneous reactions
Electrons travel through the wire from more reactive metal to the less reactive metal (Table J)
Salt Bridge – permits the flow of ions
Red Cat gets fat!

41. Electrochemistry Cell Type #2 - Electrolytic Cell
These are NOT spontaneous reactions – they are forced by the addition of electricity!
Occur within one container, not two separate cells!
These reactions are used to plate metals, purify metals and separate compounds.

42. Electrochemistry Cell Type #2 - Electrolytic Cell Cathode Anode Sn
Becomes negative Fe
Becomes positive
Picks up + ions from solution Sn
Loses positive ion (Sn+2) to solution
Gets plated with the metal ion from the solution

43. Bell Ringer
During a laboratory activity, a student reacted a piece of zinc with 0.1M HCl(aq). Based on Reference Table J, identify one metal that does not react spontaneously with HCl(aq).

44. Bell Ringer
Write out the oxidation and reduction half reactions for the voltaic cell below. (Do not need drawing in notes) K
K electrode Fe
Fe electrode
NaBr
Fe+2
K+1

45. Electrochemical Cell Differences
Electrochemistry
Electrochemical Cell Differences
Electrolytic
Voltaic
spontaneous
non-spontaneous
Anode - negative
Anode - positive
Needs two containers
Needs one container

46. Packet Review
16. K
K electrode Fe
Fe electrode
NaBr
Fe+2
K+1

47. Packet Review
16. Ag
Ag electrode Al
Al electrode
Na2SO4
Al+3
Ag+1

48. Electrochemistry Cell Type #2 - Electrolytic Cell Anode Cathode
Becomes negative
Becomes positive Zn
Picks up + ions from solution
Loses positive ion (Cu+2) to solution Cu
Gets plated with the metal ion from the solution
Cu+2
Electrons ALWAYS flow from Anode to Cathode

49. Electrochemistry
Electroplating Lab
And review packet

50. Electrochemistry Cell Type #2 - Electrolytic Cell Anode Cathode
Becomes negative
Becomes positive Zn
Picks up + ions from solution
Loses positive ion (Cu+2) to solution Cu
Gets plated with the metal ion from the solution
Cu+2
Electrons ALWAYS flow from Anode to Cathode

51. Balancing Net Ionic Equations
Electrochemistry
Balancing Net Ionic Equations
Done on the board

52. Electrolysis Simulation
Electrochemistry
Ionic equation balancing
Electrolysis Simulation

53. Balancing equations using oxidation numbers
C3H8O + CrO3 + H2SO4  Cr2(SO4)3 + C3H6O + H2O
Balancing equations using oxidation numbers

54. Try to balance this one:
BALANCING REACTIONS
conservation of mass and charge
we must make sure that the e- that one atom loses must equal the e- that another atom gains
Try to balance this one:
HNO3 + I2  HIO3 + NO2 + H2O

55. BALANCING REACTIONS HNO3 + I2  HIO3 + NO2 + H2O N+5 + 1e-  N+4
1. Assign ox #’s, write ½ reactions and cross out spectators
N e-  N+4
I e-  I+5
2. Balance each ½ reaction with respect to atoms and then e- 10 ) (
N e-  N+4 1 ) (
I e-  2I+5
3. Distribute to all parts of the ½ reaction
10N e-  10N+4
I e-  2I+5

56. BALANCING REACTIONS 10N+5 + 10e-  10N+4 I20 - 10e-  2I+5
3. Carry everything down and cross out e-
10N e-  10N+4
I e-  2I+5
10N+5 + I20  10N+4 + 2I+5
4. Put coefficients back into equation and balance what is left.
10HNO3 + 1I2  10HIO3 + 2NO2 + H2O 4

57. BALANCING REACTIONS Sb + HNO3  Sb2O5 + NO + H2O Sb0  Sb2+5 + 5e-
1. Assign ox #’s, write ½ reactions and cross out spectators
Sb0  Sb e-
N e-  N+2
2. Balance each ½ reaction with respect to atoms and then e- 3 ) (
2Sb0  Sb e- 10 ) (
N e-  N+2
3. Distribute to all parts of the ½ reaction
6Sb0  3Sb e-
10N e-  10N+2

58. Most missed Part 2 Questions
1. You have a voltaic cell with copper and aluminum as the electrodes. As the cell operates, the mass of the Al electrode decreases. Explain, in terms of particles, why this decrease in mass occurs.
2. Explain, in terms of electrical energy, how the operation of a voltaic cell differs from the operation of an electrolytic cell used in the Hall process. Include both the voltaic cell and the electrolytic cell in your answer.
3. Explain, in terms of ions, why molten cryolite conducts electricity.
[Cryolite = Na3AlF6]

59. BALANCING REACTIONS 6Sb0  3Sb2+5 + 30e- 10N+5 + 30e-  10N+2
3. Carry everything down and cross out e-
6Sb0  3Sb e-
10N e-  10N+2
6Sb0 +10N+5  3Sb N+2
4. Put coefficients back into equation and balance what is left.
6Sb + 10HNO3  3Sb2O5 + 10NO + H2O 5

60. Bell Ringer
Balance the following
S + HNO3  SO2 + NO + H2O

61. Bell Ringer
The Statue of Liberty is made of an iron framework covered by copper metal. Over time, a thin green layer(patina) forms on the outside. Where the iron came into contact with the copper a reaction occurred where the iron was oxidized. Why did this happen? Use your Reference Tables.