Ch21_3 - 1 Basic Concepts of Electrochemical Cells CHEMICAL...

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Unformatted text preview: 1 Basic Concepts of Electrochemical Cells CHEMICAL CHANGE ---> CHEMICAL CHANGE ---> ELECTRIC CURRENT ELECTRIC CURRENT Zn metal Zn metal 2 CHEMICAL CHANGE ---> CHEMICAL CHANGE ---> ELECTRIC CURRENT ELECTRIC CURRENT Zn metal Zn metal 3 Cu2+ ions Cu2+ ions With time, Cu plates out With time, Cu plates out onto Zn metal strip, and onto Zn metal strip, and Zn strip “disappears.” Zn strip “disappears.” Cu2+ ions Cu2+ ions Electrons are Electrons are transferred from Zn to transferred from Zn to Cu2+,, but there is no Cu2+ but there is no useful electric current. useful electric current. Anode Cathode •Zn is oxidized and is the reducing agent Zn(s) ---> Zn2+(aq) + 2eZn(s) aq) •Cu2+ is reduced and is the oxidizing agent is Cu2+(aq) + 2e- ---> Cu(s) aq) Oxidation: Zn(s) ---> Zn 2+(aq) + 2eZn(s) aq) Reduction: Cu2+(aq) + 2e- ---> Cu(s) aq) -------------------------------------------------------Cu2+(aq) + Zn(s) ---> Zn 2+(aq) + Cu(s) aq) Zn(s) aq) CHEMICAL CHANGE ---> CHEMICAL CHANGE ---> ELECTRIC CURRENT ELECTRIC CURRENT •To obtain a useful current, we separate the oxidizing and reducing agents so that electron transfer occurs thru an external wire. wire 4 wire 5 6 electrons electrons Zn Cu Zn2+ ions salt bridge Cu Zn salt bridge Electrons move from anode to cathode in the wire. Anions & cations move thru the salt bridge. Cu2+ ions Zn2+ ions Cu2+ ions This is accomplished in a GALVANIC or VOLTAIC cell. A group of such cells is called a battery . battery •Electrons travel thru external wire. •Electrons travel thru external wire. ••Salt bridge allows anions and cations to Salt bridge allows anions and cations to allows move between electrode compartments. move between electrode compartments. ••This maintains electrical neutrality. This maintains electrical neutrality. Electrochemical Electrochemical Cell Cell Page 1 7 Anode, site of oxidation, negative Cathode, site of reduction, positive Page 2 ...
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This note was uploaded on 12/14/2010 for the course CHEM 1e03 taught by Professor Jb during the Winter '10 term at Macalester.

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