ELECTROLYTIC DETERMINATION OF COPPER OXIDE

OBJECTIVES:

1. The student will use the electrolysis apparatus to plate a metal from solution.

2. The student will use platinum electrodes and learn about handling Pt.

3. The student will gain experience in doing a gravimetric determination without filtration.

4. The student will learn the use of time, because this experiment must be executed in one laboratory period.

PROCEDURE:

On the laboratory period preceding the electrolysis, weigh four 2-gram samples into a 100 ml. tall form beaker and cover with plastic.

NOTE: when doing four samples it is possible to plate the second sample on the first sample without removing the first plated copper. This step saves about 45 minutes. Check with the instructor the day before you plan to do the electrolysis. On the day of the electrolysis, obtain the Pt electrodes, rinse in EtOH, dry, and weight the electrodes. While the electrodes are drying, dissolve the preweighed unknown samples. To dissolve the samples add 25 mL of di, then 4 mL of conc. sulfuric acid, and 2 mL of conc. nitric acid. Heat below boiling until solution is complete. Get Dr. Sherren to help you get the electrolysis started. After the electrodes are added to the solution, you will dilute the sample with di to about 80 mL. Electrolyze the sample at 2-3 volts (1-2 amps) for 30 minutes with the stirrer operating. Stop the stirrer, leave the current on, lower the electrodes a few mm, turn the stirrer back on, and continue the electrolysis for another 10 minutes. If plating is not complete, lower the electrodes again. If plating is complete, stop. Stop the stirrer, leave the current on, raise the electrodes out of the solution, rinse with a stream of di. Turn off current, remove the copper electrode, dip into 2 di baths and 3 alcohol baths. Dry in an oven for 5 minutes at 100o C. Cool in desiccator for 10 minutes and weigh the electrode.

At the end of the day: To clean the electrode, in the hood, set up 2 conc. nitric baths, 4 di baths, and 3 alcohol baths. Dip the electrode into each of the 9 baths in rapid succession. Conc. nitric acid will dissolve Pt as well as Cu so be rapid in your dipping. The alcohol baths can be the same ones you used after the electrolysis.

NOTE: The initial sample of copper oxide should be dried for one hour at 100o C.

CALCULATION: Calculate percent copper in the sample. Include a computer print-out for the calculation.

SAFETY AND DISPOSAL INFORMATION: Dispose of all solutions in the "Cu Electrolytic WASTE" container.

CAUTION: Remember to treat all chemicals with respect.

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