1 Electrolysis Using electrical energy to produce chemical change. Sn 2+ (aq) + 2 Cl - (aq) ---> Sn(s) + Cl 2 (g) Sn Cl 2 SnCl 2 (aq)

2 Electrolysis of Aqueous NaOH Anode (+) 4 OH - ---> O 2 (g) + 2 H 2 O + 4e- Cathode (-) 4 H 2 O + 4e- ---> 2 H OH - E o for cell = V Electric Energy ----> Chemical Change

3 Electrolysis Electric Energy ---> Chemical Change Electrolysis of molten NaCl. Electrolysis of molten NaCl. Here a battery “pumps” electrons from Cl - to Na +. Here a battery “pumps” electrons from Cl - to Na +. Polarity of electrodes is reversed from batteries. Polarity of electrodes is reversed from batteries.

4 Electrolysis of Molten NaCl Figure 20.14

5 Electrolysis of Molten NaCl Anode (+) 2 Cl - ---> Cl 2 (g) + 2e- Cathode (-) Na + + e- ---> Na E o for cell (in water) = E˚ c - E˚ a = V – (+1.36 V) = V – (+1.36 V) = V (in water) = V (in water) External energy needed because E o is (-).

6 Electrolysis of Aqueous NaCl Anode (+) 2 Cl - ---> Cl 2 (g) + 2e- Cl 2 (g) + 2e- Cathode (-) 2 H 2 O + 2e- ---> H OH - H OH - E o for cell = V Note that H 2 O is more easily reduced than Na +. Also, Cl - is oxidized in preference to H 2 O because of kinetics.

7 Electrolysis of Aqueous NaCl Cells like these are the source of NaOH and Cl 2. In 1995: 25.1 x 10 9 lb Cl 2 and 26.1 x 10 9 lb NaOH Also the source of NaOCl for use in bleach.

8 Electrolysis of Aqueous NaI Anode (+): 2 I - ---> I 2 (g) + 2e- Cathode (-): 2 H 2 O + 2e- ---> H OH - E o for cell = V

9 Electrolysis of Aqueous CuCl 2 Anode (+) 2 Cl - ---> Cl 2 (g) + 2e- Cathode (-) Cu e- ---> Cu E o for cell = V Note that Cu is more easily reduced than either H 2 O or Na +.

10 Electrolytic Refining of Copper Figure 22.11, page 934 Impure copper is oxidized to Cu 2+ at the anode. The aqueous Cu 2+ ions are reduced to Cu metal at the cathode.

11 Producing Aluminum 2 Al 2 O C ---> 4 Al + 3 CO 2 Charles Hall ( ) developed electrolysis process. Founded Alcoa.