When aqueous solutions of ionic compounds are electrolyzed, the anode and cathode half-reactions may involve the electrolysis of either water species (H 2O, H+, OH-) or solute species (the cations and anions of the compound). The Electrolysis of Aqueous Sodium Chloride The reactions associated with this process are:įigure 17.19 The electrolysis of water produces stoichiometric amounts of oxygen gas at the anode and hydrogen at the anode. The industrial process typically uses a Downs cell similar to the simplified illustration shown in Figure 17.18. Metallic sodium, Na, and chlorine gas, Cl 2, are used in numerous applications, and their industrial production relies on the large-scale electrolysis of molten sodium chloride, NaCl( l). The Electrolysis of Molten Sodium Chloride
To illustrate the essential concepts of electrolysis, a few specific processes will be considered. Perhaps less familiar is the use of electrolysis in the refinement of metallic ores, the manufacture of commodity chemicals, and the electroplating of metallic coatings on various products (e.g., jewelry, utensils, auto parts). A familiar example of electrolysis is recharging a battery, which involves use of an external power source to drive the spontaneous (discharge) cell reaction in the reverse direction, restoring to some extent the composition of the half-cells and the voltage of the battery. This final section of the chapter will address an alternative scenario in which an external circuit does work on a redox system by imposing a voltage sufficient to drive an otherwise nonspontaneous reaction, a process known as electrolysis. In these cells, electrical work is done by a redox system on its surroundings as electrons produced by the redox reaction are transferred through an external circuit.
Perform stoichiometric calculations for electrolytic processesĮlectrochemical cells in which spontaneous redox reactions take place ( galvanic cells) have been the topic of discussion so far in this chapter.Compare the operation of electrolytic cells with that of galvanic cells.By the end of this section you will be able to:
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