1. Electrochem review due
May 14, 2018
5/17
Electrochem review due
5/18
Last day to turn in Mole $
Last day for thermochem corrections and retest
Electrochemistry “test”
Warm up:
1. Which element or ion is being oxidized?
2KBr + Cl2  2KCl + Br2
2. What is the oxidation number of the nitrogen in nitric acid?
3Cu + 8HNO3  3Cu(NO3)2 + 2NO + 4H2O
3. What is the missing reactant?
_____ + NH4Cl  NaCl + NH3 + H2O
4. Which is oxidized and which is reduced?   

2. Redox reactions and reduction potentials

3. Redox reactions and reduction potentials
Reduction: species gains electrons
Oxidation: species loses electrons
One cannot occur without the other
Redox reactions and reduction potentials

4. How to remember? L G E says E O R oses ains lectrons lectrons xidized
educed
How to remember?

5. O R I says I L G
xidation
eduction s s
oss
ain
How to remember?

6. Identify which species is oxidized and which is reduced.
Ex: Na + 2H+  Na+ + H2
Ex: Pb + 2Fe3+  Pb2+ + 2Fe2+
Na = Oxidized
H+ = Reduced
Pb = Oxidized
Fe3+ = Reduced
Identify which species is oxidized and which is reduced.

7. Reduction potential table
You can predict what species will be oxidized and what species will be reduced based on a reduction potential table.
Reduction potential table shows the volts (V) to reduce a species for a given half reaction.
All compared to the reduction of H+, which is given as 0V.
Reduction potential is given the variable Eored
More positive means the species is more likely (more potential) to be reduced.
Reduction potential table

9. Write the half reaction and identify the reduction potential in volts
Ex: Ag+ is reduced to Ag
Ag+ + e-  Ag
Ered = 0.80 V
Write the half reaction and identify the reduction potential in volts

10. If a species is more likely to be oxidized, it will be more negative on the reduction potential table.
You can get the oxidation potential (Eox) by flipping the reaction and changing the sign on the reduction potential.
What if it’s oxidized?

11. Write the half reaction and identify the oxidation potential in volts
Ex: Mg is oxidized to Mg2+
Mg  Mg2+ + 2e-
Eox = 2.37 V
Write the half reaction and identify the oxidation potential in volts

12. Redox reactions involve the transfer of electrons from one species to another.
For a redox reaction to occur spontaneously, the overall (total) potential must be positive.
Compare the reduction potentials of the two half-reactions. Flip the sign on the more negative potential reaction and flip the reaction.
Then add the two half reactions to get the net ionic equation. Add the two potentials to get the overall potential (Ecell): Eocell = Eored + Eoox
To add half reactions, there must be an equal number of electrons in each half reaction. You may have to multiply the half reactions to get an equal number of electrons.
However, NEVER multiply the potentials.

13. 6 moles of electrons transferred
Determine the net ionic equation between the indicated species and calculate the cell potential of the reaction. Indicate how many moles of electrons are being transferred. Ex: Nickel (Ni) and Aluminum (Al). Al3+ + 3e-  Al Eored = V Ni2+ + 2e-  Ni Eored = V 2(Al  Al3+ + 3e- ) Eorox = 1.66 V + 3(Ni2+ + 2e-  Ni) Eored = V 2Al + 3Ni2+  2Al3+ + 3Ni Ecell = 1.41 V
More negative, so flip!
6 moles of electrons transferred
Practice

14. 2 moles of electrons transferred
Determine the net ionic equation between the indicated species and calculate the cell potential of the reaction. Indicate how many moles of electrons are being transferred. Ex: Hydrogen (H2) and Fluorine (F2) 2H+ + 2e-  H2 Eored = 0 v F2 + 2e-  2F- Eored = 2.87 V H2  2H+ + 2e- Eored = 0 v F2 + 2e-  2F- Eored = 2.87 V H2 + F2  2H + + 2F- Ecell = 2.87 V
More negative, so flip!
2 moles of electrons transferred
Practice