1. 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. 2 Electrolysis of Aqueous NaOH Anode (+) 4 OH - ---> O 2 (g) + 2 H 2 O + 4e- Cathode (-) 4 H 2 O + 4e- ---> 2 H 2 + 4 OH - E o for cell = -1.23 V Electric Energy ----> Chemical Change

3. 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. 4 Electrolysis of Molten NaCl Figure 20.14

5. 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 = - 2.71 V – (+1.36 V) = - 2.71 V – (+1.36 V) = - 4.07 V (in water) = - 4.07 V (in water) External energy needed because E o is (-).

6. 6 Electrolysis of Aqueous NaCl Anode (+) 2 Cl - ---> Cl 2 (g) + 2e- Cl 2 (g) + 2e- Cathode (-) 2 H 2 O + 2e- ---> H 2 + 2 OH - H 2 + 2 OH - E o for cell = -2.19 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. 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. 8 Electrolysis of Aqueous NaI Anode (+): 2 I - ---> I 2 (g) + 2e- Cathode (-): 2 H 2 O + 2e- ---> H 2 + 2 OH - E o for cell = -1.36 V

9. 9 Electrolysis of Aqueous CuCl 2 Anode (+) 2 Cl - ---> Cl 2 (g) + 2e- Cathode (-) Cu 2+ + 2e- ---> Cu E o for cell = -1.02 V Note that Cu is more easily reduced than either H 2 O or Na +.

10. 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. 11 Producing Aluminum 2 Al 2 O 3 + 3 C ---> 4 Al + 3 CO 2 Charles Hall (1863-1914) developed electrolysis process. Founded Alcoa.