FUNDAMENTALS OF ELECTROCHEMICAL CELLS
E2
This exercise does not require a report.
PURPOSE
To observe factors that affect the potential of an electrochemical cell.
PROCEDURE
1.
The saturated calomel electrode (SCE) to be used will be need to have its electrolyte levels
checked. Your teacher will show you how this is done. From this point on, it will be your
responsibility to check this each time you use a calomel electrode.
2.
Record the cell potentials for the following combinations of half-cells. Each half-cell is to be
set up in a 150 mL beaker, with a salt bridge soaking in 1M ammonium nitrate would be
suitable.
3.
Half-cell 1 should be connected to the volts terminal, and half-cell 2 to the COM terminal.
Electrode
Half-Cell 1
Solution
Half-Cell 2
Electrode
Solution
1
Zn
Zn2+ (1 M)
Cu
Cu2+ (1 M)
2
Zn
Zn2+ (1 M)
Fe
Fe2+ (1 M)
3
Cu
Cu2+ (1 M)
Fe
Fe2+ (1 M)
4
Cu
Cu2+ (1 M)
Cu
Cu2+ (0.1 M)
5
Cu
Cu2+ (1 M)
Cu
Cu2+ (0.01 M)
6
Zn
Zn2+ (1 M)
SCE
1M NH4NO3
7
Fe
Fe2+ (1 M)
SCE
1M NH4NO3
8
Cu
Cu2+ (1 M)
SCE
1M NH4NO3
9
Cu
Cu2+ (0.1 M)
SCE
1M NH4NO3
10
Cu
Cu2+ (0.01 M)
SCE
1M NH4NO3
11
Cu
unknown Cu2+
SCE
1M NH4NO3
12
Cu
SCE
1M NH4NO3
13
Cu
Cu2+ (0.1 M) +
NaCl (5 g)
Cu2+ (0.1 M) +
5M NH3 (5 mL)
SCE
1M NH4NO3
14
Cu
Cu2+ (1 M)
Cu
unknown Cu2+
Reading
QUESTIONS
1.
(a) For cells 1-8, calculate the theoretical potential for each cell using the standard reduction
potentials in your theory notes. The displayed voltage on the multimeter is equal to the value of
half-cell 1 minus half-cell 2.
(b) Tabulate the difference between theoretical and measured values.
(c) Suggest possible causes of these differences
2.
Plot a calibration graph of the cell potentials from 8-10 against log10[Cu2+] and use this to
determine the concentration of the unknown from 11
3.
Explain the significance of the results of 12 and 13 (in terms of analysis of real samples)