Build a Battery
Metal ions and metals exhibit characteristic values of electrochemical potentials (reduction potentials) These values are of interest because they can be used to predict possible oxidation reduction reactions betwixt metals and their ions. This information can also be used to design batteries with a certain voltage. A company, Batteries-R-Us, wants you group to investigate six unknown metals for their potential to provide voltage. The company wants you to present a table of reduction potentials that looks similar to the appendix at the back of your textbook. Your values will be for 'standard state' as you will measure them with the metal solutions being 1.0 M. You know that if you change those concentrations, you can get different values for Ecell (think concentration cell) They want a battery that has a voltage of exactly 1.0000 V. You need to provide two metal combinations (four separate metals) that will generate an Ecell of 1.0000 V. Obviously you specify the concentrations of the two solutions (which will be different and not 1.0M)
The values in the appendix of your book are all based off the hydrogen electrode being 'zero'. This is an arbitrary zero point because you cannot measure just a reduction potential or just a reduction potential, you measure Ecell which is a sum of the reduction and oxidation potentials of your two half cells.
For your table, we will have to have a reference half cell
which all the other values will be based. In this experiment, you will 'set' the
reduction potential of element 'C' to be 0.0 V.
The procedure will consist of measuring the potentials of each combination of
the six metals (labeled A-F) Then deducing what the reduction potential of each
metal is. Setting the oxidation potential (and thus the reduction potential) of
C to zero makes getting values really easy. The Ecell for the A-C
potential will give you the potential (ox or red) for element A. The Ecell
for B-C will give you the potential for B. Armed with those two values you
should be able to predict what the potential for the A-B cell. Compare the
predicted value to the actual value you determined for the A-B cell. Do this for
each 'non-C' combination.
You will be given 6 unknown solutions labeled A-F, all 1.0 M, and 6 samples of metal, also labeled. The procedure for making half cells with combinations of two of these species will be shown to you by your instructor.
Report: Your report will be a professional written memo giving a brief procedure followed and a table of reduction potentials (that looks similar to the table in your textbook). You must also explain (in detail with solution concentrations) how they could build a 'wet cell' that has a voltage of 1.0000 V. Remember, you need to give them two combinations to make this 1.00 V cell). Then of course there is the little paragraph about what would make this a more effective teaching experience...
Prelab Questions (Where should I write them??)
1. For each of the following cells (the two metal/ion solutions used are given) write the balanced chemical equation and calculate the Ecell for the reaction.
a. Al/Al+3 ; Fe/Fe+2
b. Mg.Mg+2 ; Mn/Mn+2
2. Write up ( and show the instructor on your way in) some semblance of a data sheet.
~MEO 04.29.04 09:35