ELECTROCHEMISTRY

ELECTROCHEMISTRY: 12.6 ELECTROPLATING -         an electrolytic process that deposits a thin, uniform layer of metal (gold, silver, copper, nickel, chromium, zinc, or tin) on a conducting surface to enhance their aesthetical appeal or to provide corrosion protection.

-         even non-conducting bodily such as wood, plastic, or leather can be electroplated if first treated with wax or a lacquer containing graphite.

-         The electroplated object is used as the cathode of an electrolytic cell and the anode is ordinarily the electro coat metal.

-         silver cyanide, potassium cyanide and potassium carbonate distributively constitute about 4% of the electroplating solution.

-         the composition of the electrolyte varies with different plating process.

-         the electrode half-reactions are: Anode (oxidation): Ag(s) + 2CN-(aq) Ag(CN)2-(aq) + e- Cathode ( decrease): Ag(CN)2-(aq) + e- Ag(s) + 2CN-(aq) The end result is the transfer of silver from the anode to the cathode.

                          Ag(s) Ag(s)                           (anode)          (cathode) electrolytic capacitor Purification of Metals -         electrolytic cells designed for this purpose consist of some closely-packed anodes and cathodes -         anodes contain the impure metal and the cathodes are thin sheets of genuinely pure metal.

-         When cell in operation, the anodes slowly dissolve as pure metal is deposited on the cathodes. The impurities form a gunk on the bottom.

Eg. Purification of lead, the impure metal is obtained by reduction of lead(II) oxide with coke, and further reduced by carbon monoxide.

        PbO(s) + C(s) Pb(l) + CO(g)         PbO(s) + CO(g) Pb(l) + CO2(g) Anode (oxidation):         Pb(s) Pb2+(aq) +2e- Cathode (reduction):         Pb2+(aq) + 2e- Pb(s)

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