Purpose
To illustrate a non-spontaneous and spontaneous reaction.

Materials

• Copper (II) chloride, CuCl2 (1.0 M solution)
• 2 ea. graphite electrodes
• Power source (15V max.)
• Volt meter
• Electrical leads (with Alligator Clips)
• 250 mL beaker
• 100 mL graduated cylinder

Safety

• Read the MSDS/WHMIS sheets for all chemicals before using them
• Wear chemical safety glasses
• Ensure the electrodes do not touch
• The chlorine gas generated is poisonous, ensure area is well ventilated (use a fume hood)
• Clean the graphite electrodes in a fume hood due to the toxic gas generated when using nitric acid to remove the copper

Procedure

1. Add 100 mL 1.0 M copper (II) chloride solution to a 250 mL beaker.
2. Immerse a pair of clean graphite electrodes into the concentrated aqueous solution. (Can be done on a glass petri dish on the overhead).
3. Ensuring that electrodes do not touch, connecting them to a variable voltage DC power source.
4. Slowly raise the voltage.
5. Observe the voltage reading at which the reaction could be detected.
6. Leave the power on for a couple of minutes and then disconnect the power source and connect the electrodes to voltmeter.
7. Observe the voltage reading. If the voltage is zero switch the leads from the graphite electrodes on the voltmeter.
8. Remove the electrodes from the solution and observe any discoloration and odor.

Results

• When the power source is turned on and the voltage is increased copper metal will be plated onto the negative electrode and chlorine gas will be generated at the positive electrode.
• When the power source is removed a voltage is generated as the reverse reaction occurs.

Follow-up Teaching Notes

• When the graphite electrodes are connected to the power source, copper ions will be reduced to copper metal on the electrode connected to the negative terminal and chloride ions will be oxidized to chlorine gas on the other electrode.
• When the power source is used, an electrolytic cell is produced.
• After copper metal and chlorine gas are generated and the power source is disconnected a voltaic (galvanic) cell is made.
• The copper can be cleaned off the electrodes with concentrated nitric acid.

Connections
Electrolytic/ voltaic cells (electrochemical cells), spontaneous/non-spontaneous reactions.

Disposal/Clean-up
The copper (II) chloride solution can be stored in a sealed container for later reuse or it can be placed in the science department’s heavy metal waste container for proper disposal.

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