In the first part, you looked at reactivity and found Zn to be the most active metal, followed by Pb, then Cu. I'll just use those three as an example, you will also need to include Ni and Ag in your assignment. You measured the potential for a Zn/Pb cell, a Pb/Cu cell, and a Zn/Cu cell. Is there a relationship between those measured potentials? There's a relationship between those reactions, but how are cell potentials related to one another?
Zn(s) + Pb2+(aq) ⇄ Pb(s) + Zn2+(aq)
Pb(s) + Cu2+(aq) ⇄ Cu(s) + Pb2+(aq)
Zn(s) + Cu2+(aq) ⇄ Cu(s) + Zn2+(aq)
Are cell potentials like kinetics (the cell potential for the overall process is determined by the lowest potential)? Are cell potentials like equilibrium (the cell potential for the overall process is the product of the step-wise potentials)? Or is there another relationship between the step-wise potentials and the overall potential? When you think you see (observe) a relationship with the Zn/Pb/Cu system (hypothesis), check to see if the same relationship is true with some of the other cell combinations you measured.(test/experiment){Hmm, it looks like we could use the scientific method to analyze the data and results from this experiment. Who would have guessed?!}
On your hand-in assignment for lab, the "calculated" cell potentials for pairs that are not next to each other refers to the treatment you see above. You have measured all of the potentials for cell constructed from metals that are adjacent to each other in your activity series (step-wise potentials), so if there is a relationship between step-wise potentials and the potentials for cells constructed from metals that are not adjacent to each other in your activity series, you should be able to calculate the expected cell potential for those non-adjacent cells.
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