Galvanic Cells and the Nernst Equation

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Aim : a) To determine reduction potentials of several redox couples. b) To determine the effect of concentration changes on cell potential. c) To determine the molar concentration of Cu2+ in the unknown using Nernst equation. Procedure : Please refer to the laboratory manual page 77 – 79. Results : Reduction Potentials of Several Redox Couples Galvanic Cell Measured Ecell Anode Equation for Anode Reaction Cathode Equation for Cathode Reaction Cu-Zn +1.19 V Zn Zn → Zn2+ + 2e- Cu Cu2+ + 2e- → Cu Cu-Mg +3.23 V Mg Mg → Mg2+ + 2e- Cu Cu2+ + 2e- → Cu Cu-Fe +0.89 V Fe Fe → Fe2+ + 2e- Cu Cu2+ + 2e- → Cu Zn-Mg +2.00 V Mg Mg → Mg2+ + 2e- Zn Zn2+ + 2e- → Zn Fe-Mg +1.54 V Mg Mg → Mg2+ + 2e Fe Fe2+ + 2e → Fe Zn-Fe +0.29 V Zn Zn → Zn2+ + 2e- Fe Fe2+ + 2e- → Fe Balanced net reaction Cu-Zn Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s) Cu-Mg Mg (s) + Cu2+ (aq) → Mg2+ (aq) + Cu (s) Cu-Fe Fe (s) + Cu2+ (aq) → Fe2+ (aq) + Cu (s) Zn-Mg Mg (s) + Zn2+ (aq) → Mg2+ (aq) + Zn (s) Fe-Mg Mg (s) + Fe2+ (aq) → Mg2+ (aq) + Fe (s) Zn-Fe Zn (s) + Fe2+ (aq) → Zn2+ (aq) + Fe (s) Zn-Mg = + 2.00 V, Mg-Cu = + 3.23 V The cell potential of Zn-Cu = 3.23 V – 2.00 V = 1.23 V The measured cell potential of Zn-Cu = +1.19 V The value of the sum of the Zn-Mg and Zn-Cu cell potentials are nearly the same as the Cu-Mg cell potential. Zn-Fe = +0.29 V, Zn-Mg = +2.00 V The cell potential of Fe-Mg = 2.00 V – 0.29 V = 1.71 V The measured cell potential of Fe-Mg = +1.54 V The value of the sum of the Zn-Fe and Zn-Mg cell potentials are nearly the same as the Fe-Mg cell potential. Redox Couple Reduction Potential (measured) Reduction Potential (calculated) % Error Cu2+/ Cu +0.4 V +0.310 V 29% Fe2+/ Fe -0.5 V -0.440 V 14% Zn2+/Zn -0.79 V -0.76 V 4% Mg2+/Mg -2.79 V -2.41 V 16% Calculation for Reduction Potential (V) Ecell = Ecathode - Eanode

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