Electrochemistry: Voltaic Cells
Erica Lieser
Kendall Mello
CHM145D
Lauren Bottorf
April 25, 2013
Part 1
Table 1: Cathode | Anode | Observed Potential (V) | Standard Cell Potential (V) | (%) Relative Error | Copper | Zinc | 0.91 | 1.10 | 17.3 | Copper | Magnesium | 1.33 | 2.71 | 50.9 | Zinc | Magnesium | 0.48 | 1.61 | 70.2 | Copper | Aluminum | 0.65 | 2.00 | 67.5 | Aluminum | Magnesium | 0.74 | 0.71 | 4.23 |

Table 1 shows the measured potential readings and the standard cell potentials for all of the combinations above. The predicted Cu/Al potential was 1.09V which was much higher than the measured value of 0.65V. The prediction was made based on the Cu/Mg potential of 1.33V and the Al/Mg potential value of 0.74V. The prediction was that the Cu/Al value would be about halfway between these two values. The standard cell potential values are very different from the measured values. The only measurements that are relatively close are the Cu/Zn potential and the Al/Mg potential. The other measurements however differ greatly with a percent error of 50.9% or higher. The standard cell potentials are also all higher than the observed potentials except for Al/Mg. The reason for this is that water has a standard reduction potential of -0.8277V and because the solutions were only 0.01 M, it means that a large amount of the solution was water. This causes the observed voltages to be smaller than what they should be.
From part one, the reduction reactions and half-cell potentials are as follows: Reduction Reaction | Half-Cell Potentials | Cu2+(aq) + 2e- → Cu(s) | 0.34 | Zn2+(aq) + 2e- → Zn(s) | -0.76 | Mg2+(aq) + 2e- → Mg(s) | -2.37 | Al3+(aq) + 2e- → Al(s) | -1.66 |

Part 2
Table 2: