Reactivity Series and Galvanic Cells

CHEM 220 Laboratory Manual – 2012 Revision p. 1

CHEM 220 Laboratory Manual – 2012 Revision p. 2 Reactivity Series

PROCEDURE

Part 1. Reactivity Series of Metals

1. Collect 5 small pieces of each of the following metals, polish them with steel wool, rinse with DI water and place each in a separate test tube (20 test tubes total): • Copper • Magnesium • Lead • Zinc

2. For each metal, add about 1-2 mL of the following 0.1 M solutions containing the indicated cations. Add each solution to just one test tube of a particular metal; however, do NOT use the solution containing the ion of the metal. Properly label each tube with metal and solution contents. (You can use the chart below as a guide for setup.)

+ • Silver ions Ag (solution may be lower in concentration – will NOT affect results) • Hydrogen ions H+ • Copper (II) ions Cu2+ • Magnesium ions Mg2+ • Lead (II) ions Pb2+ • Zinc ions Zn2+

3. Observe the appearance of the metals and solutions initially. Observe any changes that are taking place immediately. Allow the metals and solutions to react for 15 + minutes, and then observe changes that have occurred to the solutions. Record the data in your notebook with a similar table to the one below:

Ion + + 2+ 2+ 2+ 2+ Metal Ag H Cu Mg Pb Zn

4. Based on the data collected in this part of the experiment, construct a Reactivity chart that puts the metals, including silver metal (& elemental hydrogen, H2) in order from most reactive metal (or element) to least reactive.

CHEM 220 Laboratory Manual – 2012 Revision p. 3 Part 2.A. Making a Reduction Potential Table

5. Obtain a multimeter (or voltmeter), two wires with alligator clips, and a porous cup (or salt bridge).

6. Obtain approximately 50 mL each of 0.1 M solutions with the following cations: • Copper (II) ions Cu2+ • Magnesium ions Mg2+ • Lead (II) ions Pb2+ • Zinc ions Zn2+

7. Obtain an electrode of each of these metals, polish with steel wool, and rinse with DI water.

8. Construct the following cells:

• Cu-Zn • Pb-Zn • Mg-Zn

Use the diagram of the Cu-Zn cell below as a guide:

Diagram to be drawn in class or see class notes or textbook.

In each cell, the voltage read should be a positive value. In order to read the positive voltage, the anode compartment must be attached to the negative terminal on the multimeter. If you read a voltage that is negative, switch the wires to the opposite terminals.

For each cell: Record the voltage. Record which half-cell is the anode.

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9. For these three electrochemical cells that include zinc, write the anode reaction, the cathode reaction, and write the overall chemical reaction. We will assume that the reduction potential

of the zinc half-cell is E°red = − 0.76 V. Based on zinc as a reference, calculate the reduction potentials of the other half-cells.

Organize your analysis of each half-cell following this example for Cu-Zn:

ANODE reaction:

CATHODE reaction:

OVERALL reaction:

Calculation of E°red for _____:

10. Prepare a reduction potential table for each of the half-reactions you have studied.

Put these in order from most easily reduced to least easily reduced. The entry for zinc should appear as follows:

Reduction E°

2+ Zn + 2e− à Zn(s) − 0.76 V

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Part 2.B. Using the Reduction Potential Table to Predict Cell Potentials.

11. Construct the following cells in a similar manner to the cells above and record their voltages:

• Cu-Pb • Pb-Mg • Cu-Mg

For each cell: Record the voltage. Record which half-cell is the anode.

Based on the values you determined for the reduction potentials in Part 2.A. above, calculate a predicted voltage for each ½-cell combination.

Organize your analysis of each half-cell in the following way:

ANODE reaction:

CATHODE reaction:

OVERALL reaction:

Calculated (predicted) E°cell: ______

Measured E°cell: ______

12. Diagram the Cu-Pb cell. Be sure to include all necessary components. Label cathode and anode.

CHEM 220 Laboratory Manual – 2012 Revision p. 6