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Q-7
EXPERIMENTAL METHOD
You will set up a series of voltaic cells from which quantitative measurements of electrode potentials can be
made for five half-cells and for I2/I
-
. You will be able to determine the order of displacement for the five
metals from your measurements. By testing for the displacement of halogens as discussed in the previous
section, you will qualitatively determine the order of substitution of among them. Then, by using the results
of the (I2/I
-
) half reaction, you will be able to relate the halogen substitution series to the metal substitution
series.
The apparatus in Figure 2 will be used for the quantitative measurement of electrode potentials of all
possible combinations involving the five metals and their salt solutions. A polystyrene plate with 24 flat-
bottomed wells serves as the apparatus. A solution of KNO3 is placed in a central well and strips of filter
paper extending from the KNO3 solution to the solutions in the surrounding wells will function as the salt
bridge (once saturated with KNO3). The 1.0 M metal ion solutions are in the surrounding wells and are in
contact with a strip of the corresponding metal, which acts as an electrode. Each metal strip and
solution forms a half-cell. The filter paper saturated with KNO3 serves as the salt bridge.
Figure 2
Pb
2+
Lines represent filter paper salt bridges
Filter Paper
1.100 V
Voltmeter
BLACK
RED
Zn(NO
3
)
2
(1.0 M)
KNO
3
(1.0 M)
CuSO
4
(1.0 M)
Aligator
Clip
Aligator
Clip
Zinc Metal
(strip)
Copper Metal
(strip)
SIDE VIEW
KNO
3
Cu
2+
I
2
/I
-
Ag+
Zn
2+
TOP VIEW
Cd
2+
