1. 14.2a Voltaic Cells
Basic Function

2. Voltaic Cell Basics
Electrodes and electrolytes chemically react to form ions that move in or out of solution.
= electrode where electrons are transferred out of the solution (ox. occurs)
= electrode where electrons are transferred into the solution (red. occurs)
can be a liquid or a paste
Each half-cell contains one and one

3. Voltaic Cells
device that changes chemical energy into electrical energy
involves a reaction
reducing agent transfers electrons to the oxidizing agent
oxidation:
of electrons
(  ox. state)
reduction:
(  ox state)

4. Voltaic Cells
if the two half-rxtns are combined in the same container, the electron exchange occurs directly as work and released as heat (not ideal)
to harness the energy, keep each half-rxtn in a separate container so the electron transfer occurs through a wire ( )
when the metal solid of the metal ion is not a possibility then an is used
usually carbon or platinum

5. Half-cells
A or porous disk is used to allow for unrelated ions to move between cells, allowing balance of charge
is also used

6. Particle movement which direction will the electrons flow in?
from reducing agent to oxidizing agent
Locations of each half-rxtn
anode:
oxidation/SRA
cathode:
reduction/SOA
cations --->
<--- anions

7. Cell Notation short hand for describing cells
anode is on L and cathode is on R
separate anode and cathode half-rxtn with ||
separate phases in one half-rxtn with |
electrodes go on far ends of notation
Mg(s) | Mg2+(aq) || Al3+(aq) | Al(s)
Pt(s) | ClO3-(aq), ClO4-(aq) || MnO4-(aq), Mn2+(aq) | Pt(s)

8. |------------------------- e- flow ----------------------->
anode (-) | electrolyte || electrolyte | cathode (+)
cations --->
<--- anions

9. Basic Concepts of Electrochemical Cells
Anode
Cathode

10. CHEMICAL CHANGE ---> ELECTRIC CURRENT
With time, Cu plates out onto Zn metal strip, and Zn strip “disappears.”
Zn is oxidized and is the reducing agent Zn(s) ---> Zn2+(aq) + 2e-
Cu2+ is reduced and is the oxidizing agent Cu2+(aq) + 2e- ---> Cu(s)

11. CHEMICAL CHANGE ---> ELECTRIC CURRENT
To obtain a useful current, we separate the oxidizing and reducing agents so e- transfer occurs thru an external wire.
This is accomplished in a GALVANIC or VOLTAIC cell.
A group of such cells is called a battery.

12. Salt bridge allows anions and cations to move between half cells
Zn --> Zn2+ + 2e-
Cu2+ + 2e- --> Cu
Reduction
Cathode
Positive
Oxidation
Anode
Negative
<--Anions
Cations-->
•Electrons travel thru external wire
Salt bridge allows anions and cations to move between half cells

14. Cell description Describe a voltaic Cell: balanced chemical eqtn.
give the direction of electron flow
assign the anode and cathode
give cell notation

15. Example Write balanced equation
Describe the Galvanic cell based on the following half-reactions:
Ag+ + e-  Ag
Fe3+ + e-  Fe2+
Write balanced equation
Fe half-rxtn is reversed since Fe2+ is SRA
Ag+ + Fe2+  Ag + Fe3+

16. Example Assign cathode and anode Give the direction of electron flow
oxidation: Fe2+  Fe3+ + e-
reduction: Ag+ + e-  Ag
electrons flow from Fe2+ half-cell to Ag+ half-cell
Assign cathode and anode
anode: oxidation: Fe2+  Fe3+ + e-
cathode: reduction: Ag+ + e-  Ag

17. Cell Notation
Pt(s) | Fe2+(aq), Fe3+(aq) || Ag+(aq) | Ag(s)

18. Homework Read p.622 - 626 in textbook Questions p.626 #1-8
LSM 14.2 C & D