1. ELECTROCHEMICAL CELLS
• Writing of equations representing oxidation and reduction half reactions and redox reactions
• Electrolytic and galvanic cells;
Writing Equations
• Relation of current and potential to rate and equilibrium;
• Understanding of the processes and redox reactions taking place in cells;
• Standard electrode potentials;
Calculating Ecell
Electrolysis
Rust
Industrial applications

2. M+ M+ M+ M+ + - Metal Electrodes. _ M _ e- e- O- e- H+ e- e- e- e- +
Metal atoms can leave their electrons (weakly held) and go into solution. + e-
O-
H+ + + e- M+ M+ + + + O H + + + e- O H + e- e- + + + O H + + M+ M+ e- e- + + +
An electric potential develops between the solution(….) and electrode(……). Move the red charges to show the electric potential.
M(s)  M+(aq) + e- -

3. State which ions would be OXIDISED AND WHICH WOULD BE REDUCED
Direct Contact.
Copper has a STRONGER attraction for electrons than Zinc.
Zn(s)  Zn2+(aq) + 2e- _ _ Zn
Cu2+(aq) + 2e-  Cu(s) e- O H + + e- O H + + +
Cu2+
Cu2+ O H + + +
Cu2+ e- + e-
(SO42-) e- O H + + + O H + + e-
Cu2+
Cu2+ O H e- +
The zinc rod would become layered with copper
The blue solution would become colourless
State which ions would be OXIDISED AND WHICH WOULD BE REDUCED
The copper ions are reduced to copper metal and the zinc metal is oxidised to zinc ions.

4. - Electrochemical Cell. _ _ + e- V > cathode anode KNO3(aq) Zn Cu
Two metals can react indirectly. e- V
Electrons flow through the external circuit from Zn to Cu.
Ions flow through the salt bridge (barrier).
Zinc metal is being
Copper ions are being …………...
Observations: The zinc electrode would be ………….- the copper electrode would ……………….
>
cathode
anode
KNO3(aq)
Salt bridge Zn Cu _ _
ZnSO4
CuSO4
Zn  Zn e-
Cu e-  Cu - +
Decide which electrode would be negative and which positive and put the charges over the correct electrode.

5. e- _ Electrochemical Cell. + _ _ V > Zn2++ 2e- --> Zn KNO3(aq)
Move the labels until they show the correct locations of oxidizing & reducing agents.
Electrochemical Cell.
Two metals can react indirectly. e- V
Attract elelctons weakly
> _
Zn2++ 2e- --> Zn +
KNO3(aq)
Salt bridge Zn Cu _ _
Top right reacts with bottom left.
ZnSO4
CuSO4
Cu e- --> Cu
Attract elelctons strongly
Zn  Zn e-
Cu e-  Cu
OXIDISING AGENT
oxidation
anode
OXIDISING AGENT
cathode
Zn + Cu2+  Zn2+ + Cu
REDUCING AGENT
REDUCING AGENT
reduction

6. ELECTROCHEMICAL CELLS GENERAL
A METAL IN CONTACT with a SOLUTION OF ITS IONS is known as A HALF-CELL.
M M+ + e N+(aq) + e  N(s)
When TWO HALF – CELLS are COMBINED an ELECTROCHEMICAL CELL IS OBTAINED.
OXIDATION takes place at the POSITIVE/NEGATIVE (delete incorrect one) electrode.
PLACE THE TWO SYMBOLS AT THE APPROPRIATE PLACE ON THE
DIAGRAM V
M+(aq)
M+(s)
N+(aq)
N+(s) - e-

7. CELL DIAGRAMS + - M1(s)  M1n+(aq) M2n+(aq)  M2(s)
The cell undergoing reduction (more +ve Eθ value) is assigned as the R.H.S. electrode.
M1(s)  M1n+(aq) M2n+(aq)  M2(s)
The solid line represents the phase boundary solid metal & the aqueous ions.
The double dashed line represents the salt bridge.
The cell potential is calculated by:
Eθcell = EθRHS  EθLHS
(do not change the signs of the Eθ values ) +
Phase boundary
salt bridge
Phase boundary -

8. ELECTROCHEMICAL CELLS
The Daniell cell :
Electrons flow from –ve to +ve in the external circuit.
The salt bridge allows the flow of ions and completes the circuit. ? E0
0.34
-0.76
Galvanic cell converts chemical energy to electrical energy
…….. ……….. // ………….  ………….
Zinc is ……………& copper is …………….

9. ELECTROCHEMICAL SERIES
Electrochemical half-cell potentials (Eθ) are listed from +ve to –ve values.
Electric
Potentials
Reactions written as …………………..
Positive potentials ………….. electrons are good ……………… AGENTS.
Negative potentials …………… electrons are good …………………… AGENTS.
Cu2+ + 2e-  Cu
(….)
Zn2+ + 2e-  Zn
(….)
Zn ………………. so is MORE ……………….

10. ELECTROCHEMICAL SERIES
Oxidizing
Agents
Electrochemical half-cell potentials are listed from +ve to –ve Eθ values.
Electrons flow in external circuit
REDUCING
AGENTS
Reactions written as reductions.
Positive potentials accept electrons are good OXIDISING AGENTS.
Negative potentials donate electrons are good REDUCING AGENTS.
Electrons flow in external circuit.
Reactions take place
Top LEFT to bottom RIGHT

11. ELECTROCHEMICAL SERIES
Difference = 0.8 – (-2.71)

12. STANDARD HYDROGEN ELECTRODE
H2 gas pressure of ……….
(………. kPa)
Solution of …..M H+ ions (HCl)
…………K
Eθ = ……………v
S.H.E. is ………. to set up.
……………….. standard electrodes used.

13. DETERMINATION OF CELL POTENTIALS
Standard electrode
Unknown electrode
High resistance voltmeter
N+(s)
If a cell potential of 1.45v is obtained with metal N. Then the electrode potential of N+ /N is
Salt bridge
N+(aq)
Eθ values are determined using a ……………………………… electrode.
The S.H.E is always the …………………. electrode.
Standard Conditions : ………………………………………………….
A secondary standard electrode the ………………. electrode can be used.
Eθcell= …………………………………………
Eθcell= ………………. – ……….

14. DETERMINATION OF CELL POTENTIALS
Calomel electrode
Unknown electrode
High resistance voltmeter
M+(s)
Salt bridge
M+(aq)
If the calomel electrode ( V ) is used as a standard with another electrode the cell potential is V.
By means of a calculation, identify the other metal.

15. SPONTANEOUS REACTIONS
Positive electrode
Negative electrode
M+(s)
E0 M - ve
High resistance voltmeter
N+(s)
Salt bridge
E V
E V
N+(aq)
M+(aq)

16. NON SPONTANEOUS REACTIONS
E V
E V
M+(aq)
M(s)
N(s)
High resistance voltmeter
Salt bridge
N+(aq)
N+(aq)

17. NON SPONTANEOUS REACTIONS
M+(aq)
M(s)
N(s)
High resistance voltmeter
Salt bridge
N+(aq)
N+(aq)

18. WORKED EXAMPLES
The redox couples Mn2+(aq) Mn(s) and U3+(aq) U(s) have Eθ values of –1.18 and –1.79 respectively. Determine Eθcell when they are combined and write an equation for the reaction that takes place.
2. The redox couples Co2+(aq) Co(s) and Ni2+(aq) Ni(s) have Eθ values of –0.28v and –0.23v respectively. Write an equation for the spontaneous reaction and use the Eθ values to justify your answer.

19. EXAMINATION QUESTIONS
Use the standard Eθ values for the half-equations shown below to answer the questions that follow.
MnO4-(aq)+8H+(aq)+5e Mn2+(aq)+ 4H2O(l) Eθ = +1.70v
Cl2(g) + 2e Cl-(aq) Eθ = +1.36v
Tl3+(aq) + 2e Tl+(aq) Eθ = +1.25v
AgCl(s) + e Ag (s) + Cl-(aq) Eθ = v
Determine Eθcell for the reaction of MnO4-(aq) with Tl+(aq) in acidic solution and write an equation for the reaction.
Why is it not possible to use HCl acid in the reaction above. Use the Eθ values to justify your answer.
Construct an equation for the reaction of Cl2(g) with Ag(s) and calculate the Eθ value for the reaction.

20. Electrolysis
Copper chloride
Electrolytic cell: Converts…

21. Electrolysis - Lead Bromide
PbBr2

22. Electrolysis - Lead Bromide
PbBr2

23. Purifying Copper + -
Identify the anode cathode etc

24. Extraction of Aluminium

25. ELECTROCHEMICAL CELLS
• Writing of equations representing oxidation and reduction half reactions and redox reactions
• Electrolytic and galvanic cells;
Writing Equations
• Relation of current and potential to rate and equilibrium;
• Understanding of the processes and redox reactions taking place in cells;
• Standard electrode potentials;
Calculating Ecell
Electrolysis
Rust
Industrial applications