Electrolysis electroplating

Electrochemical processes (e.g., electrolysis, electroplating, electromachirring, crrnetrt generation, and corrosion [Plate 8]) are distinguished by their occturence in a boundary region between an electrolyte (liqtrid or solid) and an electrode. The corrrse of these processes is strongly dependent on the potential at the electrode surface, the composition and stmcture of the electrode, the composition of the electrolyte, and the microstmcture of the electrolyte in the boundary layer near the electrode surface. In certain applications, the pore size and coimectivity of the electrode can also be important. 

Thus the range of applications is vast. Electroanalysis, potentiometric and voltammetric industrial electrolysis, electroplating, batteries, fuel cells, electrochemical machining, and many other related applications, including minimization of corrosion biosensors and bioelectrochemistry. 

Mercury layers plated onto the surface of analytical electrodes serve as Hquid metal coatings. These function as analytical sensors (qv) because sodium and other metals can be electroplated into the amalgam, then deplated and measured (see Electro analytical techniques). This is one of the few ways that sodium, potassium, calcium, and other active metals can be electroplated from aqueous solution. In one modification of this technique, a Hquid sample can be purified of trace metals by extended electrolysis in the presence of a mercury coating (35). 

Current density can be increased without impairing the quaUty of the copper by polishing the cathode surface by brief periodic current reversals (PCR). Reversed current electrolysis, first developed for electroplating, was tested in 1952 for copper refining. Although good results were obtained, no suitable electrical equipment for current reversal was available. The thyristor-controUed siUcon rectifier, introduced in the 1960s, provided a means for... 

Other industrial applications of electrolysis include extraction/purification of metals from ores, electroplating, and the manufacture of certain chemicals such as sodium hydroxide. In the latter, sodium chloride solution when electrolysed is converted to sodium hydroxide to produce chlorine at the anode and hydrogen at the cathode. Both of these gaseous by-products are collected for industrial use chlorine is used in the production of bleach and PVC hydrogen is used as a fuel, to saturate fats, and to make ammonia. 

Electroplating, (a) Silver ions are reduced to metallic silver by electrolysis. The silver coats the spoon to be plated, (b) The Oscar statue is gold plated. 

E.8 Copper metal can be extracted from a copper(II) sulfate solution by electrolysis (as described in Chapter 12). If 29.50 g of copper(II) sulfate pentahydrate, CuS04-511,0, is dissolved in 100. mL of water and all the copper is electroplated out, what mass of copper would be obtained ... 

Summary Electrochemistry is the study of chemical reactions that produce electricity, and chemical reactions that take place because electricity is supplied. Electrochemical reactions may be of many types. Electroplating is an electrochemical process. So are the electrolysis of water, the production of aluminum metal, and the production and storage of electricity in batteries. All these processes involve the transfer of electrons and redox reactions. 

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