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Electrolytic Cells Lesson 9 Electrolytic Cells 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. 2. 3. Nonspontaneous redox reaction Produces chemicals from electricity Forces electrolysis to occur 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. 1. Draw and completely analyze a molten NaBr electrolytic cell. Molten or (l) means ions but no water e- Electrons go from anode to cathode. DC Power Source - The positive is oxidation + e- The negative is reduction Pt Pt _ reduction cathode 2Na+ + 2e- → 2Na(l) -2.71 v + oxidation anode 2Br- → Br2(g)+ 2e-1.09 v Na+ Br cations to cathode anions to anode 2Na+ + 2Br- → Br2(g) + 2Na(l) E0 = -3.80 v The MTV is the minimum theoretical voltage required to start a reaction MTV = +3.80 v What do you do if there is water in the cell? Pb2+ reduces in water Reduction of water Treat as if it were here Water will reduce before anything below this line. Nothing below this line can reduce in aqueous solution Water reduces in a K+ solution Reduction If you have water present (aq) Take the higher reaction The strongest oxidizing agent Consider the overpotential effect 1.0 M solution Water (lower) oxidizes before F- Treat as if here Oxidation of water Br- (lower) oxidizes before water Oxidation If you have water present (aq) Take the lower reaction The strongest reducing agent Consider the overpotential effect 1.0 M solution 1. Draw and completely analyze an aqueous KI electrolytic cell. The negative is reduction DC Power Source - + Pt Pt Cation or water Reduction Cathode Consonants The positive is oxidation K+ H2 O I- For Reduction take the highest highest 1. Draw and completely analyze an aqueous KI electrolytic cell. The negative is reduction DC Power Source - The positive is oxidation + Pt Pt K+ H2 O I- Anion or water Oxidation Anode Vowels For Oxidation take the lowest lowest 1. Draw and completely analyze a molten KI electrolytic cell. The negative is reduction e- Electrons go from anode to cathode. DC Power Source - The positive is oxidation + ePt Pt _ reduction cathode 2H2O+2e- → H2(g) + 2OH-0.41 v anions to anode K+ H2 O I- + oxidation anode 2I- → I2(s) + 2e-0.54 v cations to cathode 2H2O + 2I- → H2 + I2(s) + 2OH- E0 = -0.95 v MTV = +0.95 v 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.