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A Heavy Metal Tug of War

  • Introduction
  • Results & Video
  • Materials
  • Procedure
  • Preparation & References
  • Downloads

In this activity, electrical current is created without a battery. Students will use their bodies to complete an electrical circuit where current flows between 2 metals that have a difference in reduction potential.

Electro - Chemical Potential

Metal symbol Electrical Potential
(Volts)
Gold Au(+3) +1.50
Platinum Pt (+1) +1.20
Silver Ag(+1) +0.80
Copper Cu(+2) +0.34
Lead Pb(+2) -0.13
Tin Sn(+2) -0.14
Nickel Ni(+2) -0.24
Cobalt Co(+2) -0.28
Cadmium Cd(+2) -0.28
Iron Fe(+2) -0.44
Zinc Zn(+2) -0.76
Manganese Mn(+2) -1.19
Aluminum Al(+3) -1.67
Lithium Li(+1) -3.04

The term electrochemical potential means that chemicals and chemical reactions are used as the energy source to drive electrical current. Batteries are electrochemical cells. Chemical reactions inside the battery drive electrical current through circuits. We know from the Electricity Activity that electricity is the movement of electrons through a circuit loop. Some materials are more conductive and some are better insulators. Metals are good conductors of electricity because electrons can move freely between their atoms.

Some metals attract electrons more strongly than others. When metals lose electrons, they are OXIDIZED:

M ----> M(+1) + 1e-

Rust is one form of oxidation. The green patina that forms on copper is another form of oxidation.

When positive metals ions gain electrons, they are REDUCED.

M(+1) + 1 e- ---> M

When silver is plated on to jewelry, it is reduced from silver ions in solution (Ag+) to become a solid silver metal coating (Ag). This process is called electroplating. Metals that have a greater tendency to be reduced are said to have a high standard reduction potential.

The table to the right lists the Standard Reduction Potential of several common metals in order. The metals at the top of the table have a greater tendency to gain electrons to metals at the bottom of the table. The metals at the bottom are more stable, which is one reason why gold, silver and platinum are good metals for jewelry. If a circuit is created with 2 metals with a difference in Reduction Potential, electricity will flow carrying electrons from the metal with low potential (more negative) toward the metal with high reduction potential (more positive), creating electricity.

Video & Results

closed

When the circuit is open, no current can flow and the meter will read 0.00 microAmps.

When the kids hold the 2 metal objects, they will complete the circuit and current will register on the multimeter, about 0.2 - 2 microAmps, depending on the surface area that is contact with the metals.

If they hold 2 different metals, there will be current. If they hold 2 objects made of the very same metal, there will be no current flow. Try this with 2 pieces of aluminum foil.

If water is sprayed on their hands, the contact surface is increased and the current increases.

Ask advanced students to look at the table of Reduction Potential in the Introduction and describe the flow of electrons. When the students swap the metals or the electrodes, the current will be reversed and the multimeter will read the same number (which often fluctuates) but the sign will be opposite.

Materials

  • multimeter that can measure into the microAmp range (RadioShack cat #22-813, $39.99)
  • electrical leads with alligator clips
  • sheets of metal of different types
    -- aluminum (aluminum foil, a soup can or sheet metal)
    -- copper (purchased a light switch plate, or a copper plate)
    -- iron (cast iron skillet or an iron nail)
    -- zinc (many nails and screws are coated with zinc)

Procedure

foil

  1. Connect the leads to the multimeter and clip alligator leads to the ends of the pointed leads.
  2. Clip the other end of the alligator leads to 2 different pieces of metal (ex. aluminum foil and a copper plate).
  3. Turn on the multimeter and turn the setting to microAmps. The meter should read "O". The circuit is open so there is no current.
  4. Now place one hand firmly on the aluminum foil that is in the circuit, and place the other hand on the copper plate. You have closed the circuit.

Questions: What does the multimeter read? Is current flowing?

Further investigation

  1. Reverse the electrode leads into the multimeter. How does the number change?
  2. Spray water on your hands and observe any differences.
  3. Try 2 pieces of aluminum foil. What happens? Why?
  4. Try different metal samples and predict your results.

 

Reference

This activity was adapted from "The Hand Battery" described at the Exploratorium in San Francisco.

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