Basic Concepts of Electrochemical Cells Anode Cathode 1
Basic Concepts of Electrochemical Cells Anode Cathode 1
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) ---> Zn 2+(aq) + 2 e • Cu 2+ is reduced and is the oxidizing agent Cu 2+(aq) + 2 e- ---> Cu(s) 2
CHEMICAL CHANGE ---> ELECTRIC CURRENT • To obtain a useful current, we separate the oxidizing and reducing agents so that electron transfer occurs thru an external wire. This is accomplished in a GALVANIC or VOLTAIC cell. http: //www. mhhe. com/physsci/chemistry/essentialchemistry/flash/galvan 5. swf A group of such cells is called a battery. 3
4 Zn --> Zn 2+ + 2 e- Cu 2+ + 2 e- --> Cu Oxidation Anode Negative <--Anions Cations--> Reduction Cathode Positive RED CAT • Electrons travel thru external wire. • Salt bridge allows anions and cations to move between electrode compartments.
5 Terms Used for Voltaic Cells
6 Calculating Cell Voltage • Balanced half-reactions can be added together to get overall, balanced equation. Zn(s) ---> Zn 2+(aq) + 2 e. Cu 2+(aq) + 2 e- ---> Cu(s) ----------------------Cu 2+(aq) + Zn(s) ---> Zn 2+(aq) + Cu(s) If we know Eo for each half-reaction, we could get Eo for net reaction.
TABLE OF STANDARD REDUCTION POTENTIALS oxidizing ability of ion Eo (V) Cu 2+ + 2 e- Cu +0. 34 2 H+ + 2 e- H 2 0. 00 Zn 2+ + 2 e- Zn -0. 76 To determine an oxidation from a reduction table, just take the opposite sign of the reduction! reducing ability of element 7
Zn/Cu Electrochemical Cell 8 + Anode, negative, source of electrons Cathode, positive, sink for electrons Zn(s) ---> Zn 2+(aq) + 2 e. Eo = +0. 76 V Cu 2+(aq) + 2 e- ---> Cu(s) Eo = +0. 34 V -------------------------------Cu 2+(aq) + Zn(s) ---> Zn 2+(aq) + Cu(s) Eo = +1. 10 V
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