1. AP Chem Get HW checked Take out laptops and go to bit.ly/GalCell
Today: Electrochemical Cells

2. Voltaic (Galvanic) Cell bit.ly/GalCell
1. In the model shown, which label (anode or cathode) is attached to the zinc metal and to the copper metal?
Zinc:
Copper:
anode
cathode

3. Voltaic (Galvanic) Cell
2. Which way do electrons flow through the wire, from the anode to the cathode or from the cathode to the anode?
Electrons flow from anode to cathode

4. Voltaic (Galvanic) Cell
3. For the zinc half-cell:
a. Write out the reaction happening in the zinc half-cell.
 b. is this reaction oxidation or reduction?
Zn  Zn2+ + 2e-
oxidation

5. Voltaic (Galvanic) Cell
4. For the copper half-cell.
a. Write out the reaction happening in the copper half-cell.
 b. is this reaction oxidation or reduction?
Cu2+ + 2e-  Cu
reduction

6. Voltaic (Galvanic) Cell)
5. Which ions move through the salt bridge?
6. Why do you think it’s important for ions to be able to move between the two compartments?
Na+ and NO3-
To prevent the buildup of charge

7. Voltaic (Galvanic) Cell)
Red Cat and An Ox
Reduction happens at the Cathode
Oxidation happens at the Anode
Electrons flow from anode to cathode
In a voltaic cell chemical energy is converted to electrical energy (like a battery)

8. When the switch is closed the following reaction occurs:
2 Al + 3 Sn2+ → 2 Al Sn
1. Write out the balanced oxidation half reaction. 2. Write out the balance reduction half reaction. 3. Identify the anode and the cathode in the reaction above. Anode: Cathode: 4. Draw an arrow on the diagram to mark the direction of electron flow

9. Electromotive Force (emf)
Water only spontaneously flows one way in a waterfall.
Likewise, electrons only spontaneously flow one way in a redox reaction—from higher to lower potential energy.

10. Electromotive Force (emf)
The potential difference between the anode and cathode in a cell is called the electromotive force (emf).
It is also called the cell potential and is designated Ecell.
Cell potential is measured in volts (V).
1 V = 1 J C

11. Standard Reduction Potentials
Reduction potentials for many electrodes have been measured and tabulated.
© 2009, Prentice-Hall, Inc.

12. Standard Cell Potentials
The cell potential at standard conditions can be found through this equation:
Ecell 
= Ered (cathode) − Ered (anode)
Because cell potential is based on the potential energy per unit of charge, it is an intensive property.

13. To calculate the cell potential, add up the potentials for the cathode and anode. When comparing the reactions for two metals:
the one with the more positive reduction potential will be the cathode and be reduced
the one with the less positive or more negative reduction potential will be the anode and be oxidized. You must FLIP the reduction potential that is in the table to turn it into an oxidation potential.

15. Note about HW Use the reference table for all HW questions
Use the 4 values given in the “pre-lab” only for those questions (they are different because they use a different standard)