Electric voltage can electrolyze or electroplate material {electrolysis}|. Electrolysis uses potential to drive electrochemical reaction. Electric current can split solute molecules into two ions. Mass deposited in electroplating, or split in electrolysis, is proportional to total charge transfer. Mass deposited in electroplating, or split in electrolysis, is proportional to atomic weight to ion charge ratio {chemical equivalent}.
calculation
Find material electrolyzed or electroplated, or charge needed to electrolyze or electroplate material amount, from balanced equation. From balanced equation, separate reduction and oxidation half-reactions. Note number of electrons transferred. Moles of electrons used are coulombs divided by 96,500 Coulombs. Coulombs used is current amperes times seconds. Ratio of electrolyzed or electroplated product coefficient to transferred-electron number is ratio of electrolyzed or electroplated product moles to electrons-used moles.
potential
Nernst potential is minimum voltage needed to reverse spontaneous reaction at given conditions. Concentration gradient at electrode surface can make overpotential. Total needed potential {decomposition potential} includes Nernst potential, overpotential, and electrical-resistance potential.
activation energy
Temperature, current-to-area ratio, electrode surface, and electrode type affect reaction activation energy.
types: constant current
Constant-current electrolysis is for metals with reduction potential greater than hydrogen and for potential greater than hydrogen decomposition potential. Hydrogen ions in high-acidity solution carry constant current, because they are much more numerous than metal ions. Substrate keeps hydrogen gas low, so gas does not cover hydrogen electrode. Constant current times time makes total charge.
types: constant voltage
Constant-voltage electrolysis keeps potential high enough to lower metal-ion concentration to optimum level but low enough to stop hydrogen-gas evolution or other-metal deposition. In this method, current decreases over time.
types: controlled potential
Controlled-potential electrolysis uses third electrode (SCE) as reference to keep oxidation potential at cathode constant, keep current high enough, and prevent unwanted reactions. Current decreases over time exponentially. Cathode potential determines decomposition potential, so, as metal deposits, ion concentration goes down, and decomposition potential goes up.
Physical Sciences>Chemistry>Inorganic>Oxidation-Reduction>Electrolysis
5-Chemistry-Inorganic-Oxidation-Reduction-Electrolysis
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Date Modified: 2022.0224