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R-11
Part I: The Effect of Concentration on Electrode Potentials
Instructions are given below for preparing a reference half-cell and five test solutions, all containing
AgNO3. Do not spill AgNO3 on your hands or clothes as it produces black stains which are difficult to
remove. Be sure to record the location of each solution in the well plate. The test solutions contain
AgNO3, (1.00 x 10
-1
M, 1.00 x 10
-2
M, 1.00 x 10
-3
M, 1.00 x 10
-4
M) respectively. There is no 1.00
M AgNO3 test solution in this experiment, however, we will assume that a 1.00 M AgNO3 test solution
will give a measured potential of 0.000 V when referenced to a 1.00 M AgNO3 solution (in reality, the
potential measured is between –0.002 V to +0.002 V). Stock solutions of AgNO3 have been made up
for you. The dilute solutions have had KNO3 added to them in order to keep the ionic strength constant
at 1.00 M. This way the activity of dilute solutions is kept nearly constant, although the KNO3 does not
participate in the reaction. You will use a 24-well plate as you did in the previous experiment. Make
sure that the wells are clean and dry before beginning the experiment. Using the dropper on the
reagent bottle, put
1.00 M KNO3 into a center well so that the well is about 2/3 full. Using the diagram given on page R-
9, carefully fill five wells surrounding the 1.00 M KNO3 cell with the following AgNO3 solutions: 1.00
M, 1.00 x 10
-1
M, 1.00 x 10
-2
M, 1.00 x 10
-3
M, 1.00 x 10
-4
M. Fill the wells approximately 2/3
full. Be careful not to contaminate solutions with one another.
Obtain 5 strips of filter paper approximately this size (
) to extend from the
KNO3 solution to each of the AgNO3 solutions. Obtain two
pieces of Ag foil and bend them so there
is a hook on one end. Using one alligator clip, attach one electrode to the probe of the black lead
from the voltmeter and put in the 1.00
10
-4
M solution of AgNO3. Put the other electrode in the
reference 1.00 M AgNO3 solution. To measure the voltage, press the metal probe from the red lead
firmly against the Ag electrode in the 1.00 M reference cell. Be careful not to allow the alligator
clip or the metal probe touch the solutions. The voltage is the first stable reading obtained.
Record the voltage on the Observations Sheet.
Keeping the silver electrode clipped to the black lead, remove it from the 1.00
10
-4
M solution, rinse
it with distilled water, dry it on paper towel and put it into the 1.00
10
-3
M solution. Repeat the above
