Lab 10 Electrochemical Cells
Purpose:
1.
2.
To predict the voltage and direction of electron flow of various electrochemical cells
To construct and measure the voltage of various electrochemical cells
Prelab Exercise:
Complete the following diagrams for each of the cells you will be making.
Materials:
1 voltmeter
porous cup
250 mL beaker
4 100 mL beakers
strip of aluminum
strip of copper
strip of zinc
carbon electrode
50 mL graduated cylinder
10 mL of 6.0 mol/L H2SO4(aq)
70 mL of 0.13 mol/L K2Cr2O7(aq)
80 ml of 0.10 mol/L Al2(SO4)3(aq)
80 mL of 0.10 mol/L ZnSO4(aq)
steel wool
80 mL of 0.10 mol/L CuSO4(aq)
Procedure:
1. Use labeled 100 mL beakers to obtain about 100 mL of each metal solution. Also obtain
about 75 mL of dichromate solution
2. Use a graduated cylinder to obtain 10 mL of sulfuric acid (CAUTION)
3. Add the acid to the dichromate solution (Handle this solution with care.)
4. Place the carbon electrode in a 250 mL beaker.
5. Pour the acidic dichromate solution into the 250 mL beaker
6. Clean the surface of a zinc strip with steel wool and place the strip in a porous cup.
7. Add the zinc sulfate solution to the porous cup until it is 2/3 full
8. Place the porous cup into the 250 mL beaker
9. Connect the positive (red) terminal of the voltmeter to the cathode of the cell and connect
the negative (black) terminal of the voltmeter to the anode of the cell.
10. Record the voltmeter reading in the data table.
11. Look for signs of a chemical reaction around the anode and cathode. Record any
observations in the data table.
12. Take the porous cup out of the 250 mL beaker, remove the zinc strip and pour the zinc
sulfate back into the labeled 150 mL beaker
13. Rinse the porous cup with tap water
14. Repeat steps 6-13 using aluminum strip in a Al3(SO4)3(aq) solution in the porous cup
15. Repeat using a copper strip in a CuSO4(aq) solution in the porous cup.
16. Remove the carbon electrode from the 250 mL beaker and pour the dichromate solution
back into the labeled beaker.
17. Rinse the 250 mL beaker with tap water
18. Repeat steps 6 – 13 using zinc and copper half cells
19. Repeat steps 6-13 using zinc and aluminum half cells
20. Repeat steps 6-13 using aluminum and copper half cells
21. Clean and dry the metal strips, dispose of solutions in the waste container in the fume
hood. Rinse glassware and the porous cup.
Observations:
Part A:
Positive
Electrode
Prelab Exercise
Negative
Predicted
electrode
voltage
Observed
Voltage
Zn(s)/Zn2+(aq)//Cr2O72-(aq),H+(aq),Cr3+(aq)/C(s)
Al(s)/Al3+(aq)//Cr2O72-(aq),H+(aq),Cr3+(aq)/C(s)
Cu(s)/Cu2+(aq)//Cr2O72-(aq),H+(aq),Cr3+(aq)/C(s)
Zn(s)/Zn2+(aq)//Cu2+(aq)/Cu(s)
Zn(s)/Zn2+(aq)//Al3+(aq)/Al(s)
Al(s)/Al3+(aq)//Cu2+(aq)/Cu(s)
Questions:
1.
Compare the predicted voltages with the observed voltages. Account for any differences.
2.
Why were the instructions to use 0.13 mol/L K2Cr2O7(aq) solution when all other solutions were 0.10
mol/L?
3.
What problems might be encountered in storing an acidic solution in potassium dichromate?