Electric Potential as Demonstrated in a Copper and Aluminum Human Battery

Location:

Concepts Shown:

To demonstrate the theory of electric potential, using human sweat as the electrolyte.

Equipment:

one aluminum and one copper plate about the size of your hand, DC ammeter, alligator clip wires, 2 trays big enough to hold the plates and 0.25" of water.

Procedure:

Construction: Connect the alligator clip wires to each plate and connect the other end to the ammeter. Place the plates in water and place your hands on them. A low voltage clock may be used instead of the ammeter. Presentation: Simply place your hands in the water on top of the plates and the ammeter will show a current running through it. A good way to demonstrate this is to use a projection ammeter, and have a student walk up and place his/her hands in the water on the plates. If a current doesn't show up try switching the connections on the ammeter. If this still doesn't work, clean the plates with a pencil eraser or steel wool to remove oxidation. Have two people come up, each puts one hand on a plate and then they join their other hands to complete the circuit.

Science:

This is an electrochemical reaction where the aluminum acts as the anode, and the copper as the cathode. A -2.3V potential is created by the following half-cell reactions: 2Al ==> 2Al 3+ + 6e- -3.32 3Cu2+ + 6e- ==> 3Cu -1.02 The thin film of sweat on your hand acts like an electrolyte. In the reaction your hand takes the negatively charged electrons from the copper, and in your other hand give electrons to the aluminum. At the same time excess electrons move from the aluminum to the copper through the ammeter. This flow creates the current and causes the needle to move. 2Al ==> 2Al 3+ + 6 e- -3.32 volts 3Cu2+ + 6e- ==> 3Cu -1.02 volts If you disconnect the ammeter and leave your hands on the plates, electrons pile up in the aluminum, and this pile up will create a voltage. This can be tested by connecting a voltmeter after having your hands on the plates for a while. Other: Other types of metals can be used, copper and zinc works well, and demonstrates how regular batteries work. Use a list of electric potential to demonstrate which metals would be appropriate.

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