Measuring an Electrochemical Cell Potential

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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.

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+. Answer

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.

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 solution.

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 discrepancy. Answer

Video ( 366K ) Explain why the cell potential is zero for this experiment. Answer

Video ( 455K ) Explain why the experimental design shown in the video will not work to measure a cell potential correctly. Answer

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