Because electrolytic cells require energy, they are of no use as power sources. However, electrolytic cells have some very important technological applications.

1. Production of Elements

   
   In nature, most elements occur naturally combined with other elements in compounds. Electrolytic cells are used to produce elements from their compounds.

   
   For an example of how electrolysis can be used to produce elements from a compound, consider water. Water is composed of hydrogen and oxygen. Electrolysis can be used to separate water into its component elements. However, a small technical difficulty must first be overcome. Pure water is a poor conductor of electric current. This difficulty can be overcome by adding a small quantity of an electrolyte such as sodium sulfate. This allows the flow of charge necessary for the transfer of electrons. The solution within the apparatus is electrolyzed, and the gases are collected in a chamber above each inert electrode.

   
   Reduction occurs at the cathode:

   \( \mathrm { 2 H_2O(l) + 2 e^- \rightarrow H_2(g) + 2 OH^-(aq) } \)

   
   Oxidation occurs at the anode:

   \( \mathrm { 2 H_2O(l) \rightarrow O_2(g) + 4 H^+(aq) + 4 e^- } \)

   
   Net equation for reaction:

   \( \mathrm { 2 H_2O(l) \rightarrow O_2(g) + 2 H_2(g) } \)
   

   
   

   
   Because oxygen and hydrogen are produced, bubbling occurs on the surface of the electrodes.

   
   Notice that two moles of hydrogen gas are produced for every one mole of oxygen gas produced.
   

   Recall Avogadro's theory. At the same temperature and pressure, each mole of gas occupies the same volume. Because two moles of hydrogen gas are being produced, hydrogen will occupy a volume twice as large as the oxygen gas does.

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2. Refining of Metals

   
   Electrolytic cells can be used to refine and purify metals. During the process of electrorefining, an electrolytic cell is used to obtain high-grade metal at the cathode from an impure metal at the anode.

   
   An alternate method of purifying metals is electrowinning. During this process, metal cations from a molten or aqueous electrolyte are reduced to form pure metal.

   
   Most metals are found in nature as ionic compounds. Typically, the production of metals from these compounds involves placing the molten ionic compound in an electrolytic cell with inert electrodes. For example, scandium metal and chlorine gas are produced by the electrolysis of molten scandium chloride. The only ions present in the electrolytic cell are Sc³⁺(l) and Cl^- (l).
   

   cathode:	\(\mathrm { 2[ Sc^{3+}(l) + 3 e^- \rightarrow Sc(s) ] } \)
   anode:	\( \mathrm { 3[ 2 Cl^-(l) \rightarrow Cl_2(g) + 2 e^- ] } \)
   net:	\( \mathrm { 2 Sc^{3+}(l) + 3 Cl^-(l) \rightarrow 2 Sc(s) + 3 Cl_2(g) } \)

   
   Notice that this reaction would not have been possible in an aqueous solution because water is a stronger oxidizing agent than aqueous scandium ions are. The water would preferentially accept the electrons, not the scandium ions. That is why the scandium chloride had to be melted rather than dissolved.

   
   Many other metals can also be formed from their molten salts using electrolytic cells. Watch the following animation to see how pure lead is produced from molten lead bromide.
   
   

   

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3. Electroplating

   
   Metals such as gold, silver, zinc, and chromium are very resistant to corrosion. However, to make many products entirely from these metals is impractical. The cost would be prohibitive and some of these metals lack sufficient strength and/or hardness. A solution is to make products from a strong inexpensive material (such as steel) and then coat the product with the more expensive metal to improve the product’s appearance or resistance to corrosion. This process is known as electroplating and represents another practical application of electrolytic cells.
   
   

   Electroplating is a process in which a metal is deposited on the surface of an object placed at the cathode of an electrolytic cell.

   
   Note that toxicity issues are associated with some metals and substances used in electroplating. Careful treatment of chemical waste is essential if these industries are to demonstrate environmental sustainability.

Check Your Understanding

Complete Section 14.3 Question 15 on page 651 of the textbook. Click the link below to check your work.