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