Experimental Procedure and Data

1. Connect the Vernier voltage probe into thee Logger Pro. Turn on the instrument. Start the Logger Pro.

Part A: Determining the Cell Potential for Redox Couples.

1. Obtain 10-20 mL of 1 M KNO3 in a 50 mL beaker. Cut 6 pieces of string, each with a length of approximately 2-3 cm. Place the pieces of string in the KNO3 solution. You need to completely saturate the string prior to use. This will be your salt bridge.
2. Obtain 3 pieces of each metal samples used in this experiment. Sand both sides of the metal samples to produce a shiny surface. If the surface is oxidized, it will prevent an accurate measurement from being recorded.
3. Make observations about each metal in the data section.
4. Obtain a well-spot plate.
5. See the diagram below for help. Fill the wells in the spot plate with a 1 M solution of the metal nitrate indicated. You need each well to be ~ 3⁄4 full. Make observations about each of the solutions in the data section.
6. Use forceps to place a piece of string (soaked in your salt solution) as indicated below. Each end of the string will be immersed in a different metal solution.
7. Attach one metal to the positive (red) lead of the voltage probe. Attach the other metal to the negative (black) lead of the voltage probe. Place each metal into THE SAME metal solution (the copper metal goes to the copper nitrate solution, the zinc metal should go in the zinc nitrate solution, etc). Wait approximately 5 seconds before recording the voltage.
8. If you obtain a negative voltage, reverse which electrode is attached to each metal

9. Record the voltages in your data section.
10. Write the correct equation for each redox reaction in the space provided.
11. Dry each of the metal samples and return them to the tray.
12. Dispose of all waste in the CHM 112 Waste container.
13. A short list of relevant published standard reduction potentials is attached below for help in comparingyour experimental data to the theoretical values.

 

Pre-lab Assignment/Questions

N o t e – this pre-lab must be finished before you come to lab.

1. In a galvanic cell,

a. Where does reduction occur?

b. Where does oxidation occurs?

c. Anions from the salt bridge flow toward the (which electrode)?

d. Cations from the salt bridge flow toward the (which electrode?

2. Consider a galvanic cell consisting of
Fe2+ + 2e- → Fe E0red = -0.44 V

Al3+ + 3e- → Al E0red = -1.66 V

a. Write the reaction occurring at the anode:

b. Write the reaction occurring at the cathode:

c. Write the reaction for the galvanic cell.

d. Calculate the E0cell for the cell.

Experimental Data and Results

Part A: Determining the Cell Potential for Redox Couples.

*Show an example of all calculations

1. Using your data create an activity series based on the reduction potentials you found.

2. Does this activity series agree with the published data? If not, give at least two plausible explanations for what may have occurred.

 A positive potential is recorded when copper is attached to the positive (red) electrode. Based on this, do you think copper is the cathode or the anode of the cell? Explain your reasoning/

1. If your string was not saturated with salt solution, would the potential of the cell have been recorded as too high, too low, or unaffected? Explain your reasoning.

 In your Cu-Zn cell you could adjust the concentration of Zn2+ and Cu2+ to maximize cell potential. Would you increase or decrease the copper concentration? Would you increase or decrease the zinc concentration? Explain your reasoning for each choice.