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Q-9
I
-
(as 0.10 M KI)
EXPERIMENTAL PROCEDURE
Part I. Quantitative Measurement of Electrode Potentials
A. Preparation of half-cells
Get a polystyrene 24-well plate from the side bench. Make sure that the wells are clean and dry
before beginning the experiment. Put about 1.5 mL of 1.0 M KNO3 into one of the inner wells of the
plate so that the well is about 2/3 full (see top view, Figure 2).
Obtain from the stock bottles 2.5 cm strips of copper, zinc, cadmium, silver and lead. If necessary, use
emery cloth or fine sand paper to clean the surface of the zinc and copper strips. Bend each strip of metal
so that it hooks over the lip of one of the wells that surround the KNO3 solution.
NOTE: The strips have color coded markings on one end. DO NOT immerse the colored
ends in the metal salt solutions.
Add the corresponding metal salt solution to each well (for example, CuSO
4
to the well with the Cu strip).
You should not fill the well more than two-thirds full. Be careful not to contaminate solutions with one
another. Check to make sure the metal strips extend below the surface of the salt solution. If they do not,
bend the metal strips more carefully.
Next, place cut filter paper strips into the wells so that one end dips into the KNO3 solution and the other
end dips into one of the salt solutions (filter strips should be approximately this size:
). It is best to grasp the filter paper in the form of a V and dip the two ends
simultaneously into the two solutions. Again be careful not to contaminate solutions. Do not get solutions
on your hands or clothes as some of them cause stains. Use a Pasteur pipet if you need to adjust filter
paper or metal strips. Try to keep the filter paper strips separated in the KNO3 solution so that they do
not overlap each other.
B. Measuring Cell Potentials
Set the selector switch on your voltmeter to the appropriate DCV scale (ask your laboratory instructor if
you are not sure). You will record all results (both positive and negative cell potentials).
