Electrochemical Cells Lab

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Determination of an Electrochemical Series
In electrochemistry, a voltaic cell is a specially prepared system in which an oxidation-reduction reaction occurs spontaneously. This spontaneous reaction produces an easily measured electrical potential which has a positive value. Voltaic cells have a variety of uses and you commonly refer to them as a “battery”. Half-cells are normally produced by placing a piece of metal into a solution containing a cation of the metal (e.g., Cu metal in a solution of a soluble salt that releases Cu2+ or Cu+ into solution). In this micro-version of a voltaic cell, the half cell will be a small piece of metal placed into three drops of a solution on a piece of filter paper. The solution contains a cation of the solid metal. Figure 1 shows the arrangement of the halfcells on the piece of filter paper. The two half-reactions are normally separated by a porous barrier or salt bridge. Here, the salt bridge will be the filter paper soaked in an aqueous solution of potassium or sodium nitrate. Using a voltmeter, the positive terminal (or lead) makes contact with one metal and the negative terminal with another. If a positive voltage is recorded on the meter, the cell you have constructed is spontaneous and you have connected the cell correctly. To construct a spontaneous cell, attach the metal having a higher, more positive, reduction potential to the positive terminal which is the cathode. The metal attached to the negative terminal is the anode and has the lower, more negative, reduction potential.

By comparing the voltage values obtained for several pairs of half-cells, you can establish the reduction potential sequence for the five metals in this lab.

M1

M2

M5

M3

M4

                                                                                                    Figure 1 

OBJECTIVES
In this experiment, you will
• Prepare micro voltaic cells and measure their potential relative to a standard electrode. • Use the relative potentials determined to construct numerous spontaneous voltaic cells. • Calculate the percent error between your calculated and measured voltage values.

Adapted from Advanced Chemistry with Vernier & Laboratory Experiments for Advanced Placement Chemistry by Sally Ann Vonderbrink, Ph. D.

Determination of an Electrochemical Series

MATERIALS
Data Collection Mechanism computer or handheld Voltage Probe Petri dish with filter paper to fit scissors sandpaper or steel wool forceps set of plastic Beral pipets Small samples of each of five metals 1 M KNO3 or NaNO3 solution 1.0 M solutions of each of the five metals labeled M12+ through M52+ (pay attention to the charge on the metal, they may not all be 2+ ions)

PROCEDURE
1. Obtain and wear goggles. 2. Either set up a voltmeter or set up the data collection system that connects an interface to the computer or handheld with the proper interface cable if necessary. a. Connect the Voltage Probe to the interface. b. Run the data collection program. c. You may gather the data with Selected Events, or simply record the readings from the main screen. 3. Obtain a piece of filter paper that fits your Petri dish and draw five small circles with dotted connecting lines, as shown below. Using scissors cut out the pie-shaped wedges between the circles as shown. Label the circles M1, M2, M3, M4, and M5.

4. Obtain the five pieces of metal. Using either sand paper or steel wool, scrub both sides of each piece of metal until shiny. Use the metal that is obviously copper as your reference metal M1.

M1

M2

Use scissors to cut out wedge.

M5

M3

M4

Adapted from Advanced Chemistry with Vernier & Laboratory Experiments for Advanced Placement Chemistry by Sally Ann Vonderbrink, Ph. D.

Determination of an Electrochemical Series

5. Place 1-2 drops of each solution on its circle (e.g., M12+ on circle labeled M1). Then place the piece of M1 metal (copper) on the wet spot with its respective...
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