1. Electrolytic Cells Lesson 9 Electrolytic Cells

2. Notes on Electrolytic Cells An electrolytic cell is a system of two inert (nonreactive) electrodes (C or Pt) and an electrolyte connected to a power supply. It has the following characteristics 1.Nonspontaneous redox reaction 2.Produces chemicals from electricity 3.Forces electrolysis to occur

3. Electrolytic Cell The electrode that is connected to the -ve terminal of the power supply will gain electrons and therefore be the site of reduction. Oxidation always occurs at the anode and reduction at the cathode Electrons flow through the wire and go from anode to cathode Anions (- ions) migrate to the anode and cations (+ions) migrate towards the cathode.

4. 1. Draw and completely analyze a molten NaBr electrolytic cell. Pt DC Power Source - + DC Power Source - + Electrons go from anode to cathode. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v 2Na + + 2Br - → Br 2(g) + 2Na (l) E 0 = -3.80 v e-e- e-e- MTV = +3.80 v The negative is reduction The positive is oxidation The MTV is the minimum theoretical voltage required to start a reaction Molten or (l) means ions but no water cations to cathode anions to anode

5. What do you do if there is water in the cell?

6. Reduction of water Water will reduce before anything below this line. Nothing below this line can reduce in aqueous solution Pb 2+ reduces in water Water reduces in a K + solution Treat as if it were here

7. Reduction If you have water present (aq) 1.0 Msolution Take the higher reaction The strongest oxidizing agent Consider the overpotential effect

8. Oxidation of water Treat as if here Br - (lower) oxidizes before water Water (lower) oxidizes before F -

9. Oxidation If you have water present (aq) 1.0 Msolution Take the lower reaction The strongest reducing agent Consider the overpotential effect

10. 1. Draw and completely analyze an aqueous KI electrolytic cell. Pt DC Power Source - + DC Power Source - + K+H2OI-K+H2OI- The negative is reduction The positive is oxidation Cationor water Reduction Cathode Consonants

11. highest For Reduction take the highest

12. 1. Draw and completely analyze an aqueous KI electrolytic cell. Pt DC Power Source - + DC Power Source - + K+H2OI-K+H2OI- The negative is reduction The positive is oxidation Anionor water Oxidation Anode Vowels

13. lowest For Oxidation take the lowest

14. 1. Draw and completely analyze a molten KI electrolytic cell. Pt DC Power Source - + DC Power Source - + Electrons go from anode to cathode. K+H2OI-K+H2OI- _ reduction cathode 2H 2 O+2e - → H 2(g) + 2OH - -0.41 v + oxidation anode 2I - → I 2(s) + 2e - -0.54 v 2H 2 O + 2I - → H 2 + I 2(s) + 2OH - E 0 = -0.95 v e-e- e-e- MTV = +0.95 v The negative is reduction The positive is oxidation cations to cathode anions to anode

15. The overpotential effect is a higher than normal voltage required for the half reaction. This is often due to extra voltage required to produce a gas bubble in solution.