The electrodes in both Electrolytic and Galvanic Cells are defined by the chemistry that occurs at a given electrode. The anode is always the site of oxidation and the cathode is the site of reduction. In electrolytic cells, the electrodes are connected to a power source because the chemistry of the electrolytic process is not spontaneous. The electrode connected to the positive terminal of the power source is positive in an electrolytic cell and drives the oxidation of negative ions attracted to that electrode. The electrode attached to the negative terminal of the power source is negative in an electrolytic cell and reduces positive ions attracted to that electrode. In Galvanic Cells the chemistry is spontaneous and the charges on the electrodes are a result of oxidation and reduction reactions occurring in a closed circuit. The anode and cathode are paired reactions (see a reduction potential table) that spontaneously undergo oxidation and reduction when coupled in a special configuration called a Voltaic Cell. The anodic reaction (as in the electrolytic cell) is the site of oxidation but unlike the electrolytic process, the anodic material undergoes oxidation and delivers a cation into solution leaving the anode with a surplus of electrons and hence a negative charge. The cathode in the galvanic cell is positive because cations in solution migrate (attracted) to the electrode and remove electrons from that terminal resulting in reduction of that cation and formation of the basic neutral element that typically leaves the system as a ppt, weak electrolyte or gas decomp. product of the reaction. Hope this helps. Good luck ...
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Which electrode (anode or cathode) is designated as positive in an electrolytic cell?
anode****
cathode
both
neither
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There are also some great links online that illustrate the processes in both types of cells. DrReb048(at)g.m.a.i.l(dot)c.o.m
2 answers