Measuring an Electrochemical Cell Potential
An electrochemical cell consists of two half-cells connected
by a salt bridge and a wire. When a voltmeter is connected into
the circuit, the potential of the cell may be measured.
More information about electrochemical cells
In this module, one type of cell set-up is described. However,
many other ways of assembling a cell are possible. Any cell will
consist of two half cells, a salt bridge, and a wire, and all
cells operate on the same basic principles.
design described in this module
includes two solutions connected by a string salt bridge
and a voltmeter (voltmeter not shown).
Will reduction occur at the anode or cathode when an electrochemical
cell causes current to flow? Answer
Given the following information:
If a half cell is arranged such that tin metal is dipped into
a solution of SnCl2 and silver metal is dipped into
a solution of AgNO3, the metals are connected by a
wire, and a salt bridge is placed between the two solutions, ________
will be oxidized and ________ will be reduced. Fill in the blanks
with Sn, Sn2+, Ag, or Ag+.
Preparing the Meter
In this module, one type of multimeter is used to demonstrate
how to measure a cell potential, but any type of voltmeter or
multimeter may be used.
To use the multimeter, the leads must be connected correctly
and the appropriate setting must be used.
Video: Connecting the leads (
1.74 M ) Text description
The multimeter must be on the setting with the V with dashed
lines, rather than on the V~ setting. Why?
Check that the voltmeter is working properly by zeroing it.
Assembling the Cell
Fill two small clean, dry beakers or cups with the two metal
salt solutions. Then prepare the metal strips. The strips must
be sanded to work properly in the experiment. Why?
Video: Preparing the metal strips
( 4.14 M ) Text description
Next, prepare the salt bridge. In this example, a piece of
string soaked in a salt solution is used, but many other types
of salt bridges are possible.
Video: Making the salt bridge
( 4.62 M ) Text description
Finally, the salt bridge must connect the two half cells.
To make the connection, place one end of the bridge into one of
the salt solutions and the other end of the string into the other
Measuring the Cell Potential
For convenience, while the metal strips are held by the alligator
clips, bend the strips into approximately ninety degree angles.
Finally, complete the cell and measure the voltage.
Video: Measuring the cell potential
( 2.40 M ) Text description
The measured cell potential should have a positive value.
If the meter displays a negative reading, remove the metals from
the alligator clips and place the metal that was in the red clip
into the black clip and the metal that was in the black clip into
the red clip. Re-measure the potential. The value displayed by
the meter should now be positive. When the meter displays a positive
value, the metal in the red clip is being reduced and the metal
in the black clip is being oxidized.
For several reasons, in some experiments the value displayed
by the voltmeter will gradually and steadily decrease. In this
case, the first value displayed should be recorded as the potential
of the cell.
Video: Downward "ramping"
of an electrochemical cell potential ( 499K )
Video ( 784K )
The strip of zinc metal shown in the video was used in a nickel/zinc
cell. Although the expected potential for this cell is 0.513 V
(as calculated from standard reduction potentials in the electrochemical
series), the measured potential was only 0.326 V. Explain this
Explain why the cell potential is zero for this experiment.
Explain why the experimental design shown in the video will
not work to measure a cell potential correctly.
Copyright © 1995-1996 NT Curriculum Project, UW-Madison