Electrolytic Cells

Source: Smaa Koraym at Johns Hopkins University, MD, USA

1. Preparation of the LaboratoryExpand

   Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.

   • Put on a lab coat, splash-proof safety glasses, and nitrile gloves. You'll prepare a concentrated solution of copper sulfate in sulfuric acid, which must be prepared in a fume hood. Be sure to keep plenty of baking soda available in order to neutralize spills.
   • Make 6 L of copper sulfate in sulfuric acid solution. Place a large magnetic stir bar inside a 6-L Erlenmeyer flask. Set the flask on the stir plate, but don't turn on the stir setting yet.
   • Carefully, pour approximately 250 mL of sulfuric acid into a 400-mL beaker.
   • Use a graduated cylinder to measure 250 mL of sulfuric acid and transfer it to the flask.
   • Measure 5 L of very hot tap water and transfer it to the flask as well. Be aware that the solution will get very hot.
   • Turn on the stir setting and let the solution mix.
   • Weigh 2.2 kg of copper sulfate and add it incrementally to the flask, allowing each addition to dissolve before adding the next.
   • Once the copper sulfate has dissolved, add another liter of hot tap water to the flask.
   • As the solution is stirring, obtain a 10-L carboy and label it as 'Concentrated CuSO₄’.
   • Carefully transfer the homogeneous solution from the flask into the carboy. Rinse the flask with 2 more liters of hot water and pour the solution into the carboy.
   • Store the capped carboy in a corrosives cabinet until you are ready to begin the lab.
   • Each group will need 50 mL of acetone, so be sure to have enough for all groups. Note: Acetone is highly flammable; therefore, it should be stored in a flammables cabinet until the lab class.
   • Each group will need a 1 x 9 cm strip of copper sheet. The copper sheet is already pre-cut, so count out the number of strips needed–one for each group.
   • Obtain a roll of 18-gauge copper wire and cut it into 3-in long pieces. Each group will need one piece, so cut as many as is needed.
   • Cut a sheet of emery paper into 1 by 2-inch pieces. Each group will also need one 10-ohm resistor, so set out a container of those in a common area along with the copper sheet, copper wire, and emery paper.
   • Provide a labeled 20-L container in the hood for organic waste.
   • Set out the following equipment and glassware at each lab station (suggested that students work in pairs):

     1    Stir plate

     2    Disposable pipettes

     1    Stir bar

     1    Current probe and data acquisition system

     1    Flash drive

     2    50-mL beaker

     1    250-mL beaker

     1    Watch glass

     1    1.5-V battery

     3    Electrical wires with alligator clips

     1    Brass key