1. Electrochemistry Introduction Voltaic Cells

2. Electrochemical Cell  Electrochemical device with 2 half-cells with electrodes and solutions  Electrode—metal strip in electrochemical cell, one in each solution

3. 2 types of electrochemical cells 1)Voltaic Cells 2)Electrolytic Cells  Still dealing with oxidation-reduction reactions  Physical separation of oxidation and reduction processes

4. 1) Voltaic Cells  “simple battery”  Electric current generated from a redox reaction in an electrochemical cell  Pathway of electron transfer  Always spontaneous  Physically separates oxidation process from reduction process

6. Voltaic Cell—Oxidation Process  Anode  Electrode where oxidation occurs  Negative charge, source of electrons  electrons migrate out through connecting wire  GIVING UP ELECTRONS !!

8. Voltaic Cell—Reduction Process  Cathode  Electrode where reduction occurs  Positive charge, electron receiver, ion source  Metallic ions (positive ions) move to electrode surface and accept electrons coming from the anode through the connecting wire.  Metallic ions converted to solid metal on the electrode

10. Salt Bridge  U-shaped tube containing a soluble salt in a saturated solution  Maintains electrical neutrality within cell solutions  Electrons do NOT go through bridge, only through wire  No acting role in redox reaction

12. General Points for Voltaic Cells  Electrons move from ANODE (-) to CATHODE (+)  Electron movement through the connecting wire generates an electric current that can be utilized.

14. Cell Diagrams  Representation of an electrochemical cell, short-hand method to actual drawing of cell  Anode---  Left portion  Cathode---  Right portion  Single line—  Boundary between electrode and solution  Double line—  Represents salt bridge

15. Example 1:  Oxidation: Zn (s)  Zn +2 + 2e -  Reduction: Cu +2 + 2e -  Cu (s) Remember to combine reactions by balancing elements and electrons in half reactions.

16. Example 2:  Oxidation: 2Na (s)  2Na + + 2e -  Reduction: Ni +2 + 2e -  Ni (s)

17. Example 3:  Write the equation for the redox reaction occurring in this voltaic cell. Al (s) Al +3 (aq) H + (aq) H 2(g) Pt (s)

18. Example 4:  Write the equation for the redox reaction occurring in this voltaic cell. Mg (s) Mg +2 (aq) Cu +2 (aq) Cu (s)

19. Homework  p. 673 #1-3