Half Cell / redox potentials. Context. Task. Evaluation

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Joel Dawson
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Half Cell / redox potentials Context Students often struggle when asked to apply redox potentials and to combine reduction half equations correctly.

1 Half Cell / redox potentials Context Students often struggle when asked to apply redox potentials and to combine reduction half equations correctly. This activity aims to involve all the individuals in a group at once and in a mutually supportive way. Task Give each student one or two of the half cell cards and pair them up. Between them they randomly put the cards into pairs, then answer the questions, swap cards, and pair up with a different student. Evaluation This is a simple task but students were absorbed and usefully focused on this for around 40 minutes. Can extend by asking the pairs to draw labeled diagrams of the cell formed or by giving full explanations as to why the proposed overall reaction is feasible. [original Reference

2 MnO H + + 3e - MnO2 + 2H2O K + + e - K E o = V E o = V effect on E o cell of increasing [MnO4 - ] effect on E o cell of increasing temperature if the overall cell reaction is exothermic Ca e - Ca E o = V F2 + 2e - 2F - E o = V effect on E o cell of increasing [F - ] effect on E o cell of increasing temperature if the overall cell reaction is exothermic Pb e - Pb 2+ E o = V effect on E o cell of increasing [Pb 4+ ] Mg e - Mg E o = V if the overall cell reaction is exothermic

3 Pt e - Pt E o = V Al e - Al E o = V effect on E o cell of decreasing [Pt 2+ ] if the overall cell reaction is endothermic MnO H + + 5e - Mn H2O V e - V E o = V E o = V effect on E o cell of decreasing [MnO4 - ] Hg e - Hg E o = V effect on E o cell of decreasing [Hg 2+ ] effect on E o cell of decreasing [V 2+ ] Zn e - Zn E o = V if the overall cell reaction is exothermic

4 Cl2 + 2e - 2CI - E o = V Cr e - Cr E o = V effect on E o cell of increasing Cl2 pressure if the overall cell reaction is endothermic Cr2O H + + 6e - 2Cr H2O Fe e - Fe E o = V E o = V effect on E o cell of decreasing [Cr 3+ ] effect on E o cell of decreasing [Fe 2+ ] MnO2 + 4H + + 2e - Mn H2O Cr 3+ + e - Cr 2+ E o = V E o = V effect on E o cell of decreasing [MnO4 - ] effect on E o cell of increasing [Cr 2+ ]

5 Br2 + 2e - 2Br - E o = V V 3+ + e - V 2+ E o = V effect on E o cell of increasing [Br - ] if the overall cell reaction is endothermic Hg e - Hg E o = V Ni e - Ni E o = V effect on E o cell of decreasing [Hg 2+ ] effect on E o cell of increasing [Ni 2+ ] Ag + + e - Ag E o = V Sn e - Sn E o = V effect on E o cell of decreasing [Ag + ] effect on E o cell of increasing [Sn 2+ ]

6 I2 + 2e - Br2 + 2I2e - E - o = 2Br E o V = V 2H + + 2e - H2 E o = 0.00 V reduction reduction or oxidation or oxidation half cell half cell positive positive or negative or negative electrode electrode identify identify the oxidising the oxidising or reducing or reducing agent agent write the write overall the overall reaction reaction equation equation calculate E o cell direction direction of electron of electron flow flow o - effect on E o cell of decreasing [I - ] if the overall cell reaction is endothermic Fe 3+ + e - Fe 2+ E o = V Cu 2+ + e - Cu + E o = V identify the oxidising Ag + + e - or Ag reducing E o = + agent 0.81 V effect on E o cell of decreasing [Fe 2+ ] Cu write e the - Cu E overall reaction o = V equation effect on E o cell of increasing [Cu 2+ ] Sn e - Sn 2+ E o = V effect on E o cell of increasing [Sn 2+ ]

(aq) 5VO2 + (aq) + Mn 2+ (aq) + 10H + + 4H 2 O. (aq) 5VO2 + (aq) + Mn 2+ (aq) + 2H + (aq) basic solution. MnO2 + 2H 2 O) 3H 2 O + I IO 3

(aq) 5VO2 + (aq) + Mn 2+ (aq) + 10H + + 4H 2 O. (aq) 5VO2 + (aq) + Mn 2+ (aq) + 2H + (aq) basic solution. MnO2 + 2H 2 O) 3H 2 O + I IO 3 Chem 1515 Section 2 Problem Set #15 Spring 1998 Name ALL work must be shown to receive full credit. Due Due in lecture at 1:30 p.m. Friday, May 1st. PS15.1. Balance the following oxidation-reduction reactions