University of Virginia
Physics Department

The Chemical Switch

A Physical Science Activity

Student Activity


**Note - Students are to be aware that connection wires to the battery is the last step for part 1.


Part 1:

  1. Strip the insulation from each end of the 3 wire sections.
  2. Place one wire section end through the opening of the ring terminal and across the ring.
  3. Wrap the wire end around the ring edge to secure.
  4. Indent the wire across the ring opening to support the light bulb underneath.
  5. Take another section of electrical wire and wrap the end around the bulb. * This would be at the top of the metal casing, but under the bent edge of the bulb. The tightly wrapped wire is held in place with a small piece of electrical tape.
  6. Put the bulb with the attached wire onto the indented wire across the ring opening.
  7. Secure all parts together with electrical tape.
  8. Connect the free ends of the wire to the battery and test for closure of the circuit.
    ****Time is given for readjustments in the circuit permitting student decision making.

Part 2:

  1. Mass the selected solute in several gram parts or allotments. This may be by 10 or 20 grams portions until or if you reach the 100 gram addition.
  2. Place 450 to 500 mL of water in a beaker.
  3. Mark very clearly the beginning water level with a marker or a rubber band.
  4. Place the ends of the wires from Part 1 into "pure" water.
  5. Look for changes at the ends of the wires.
  6. Observe for conductivity.
  7. Add for 10 or 20 grams of solute to the water. Test with battery and bulb.
  8. Continue to add solute by 10 or 20 gram increments or portions and test for conductivity.
  9. Record results in the table
  10. Calculate the solute concentration for each trial, using the formula, Mass/Volume.
  11. Identify the concentration that initiates conductivity

Part 3:

  1. Make observations of the very small bubbles coming from the wire ends into the solution. This should be done at the initial hook-up of the battery. This observation will be the "point of comparision" for bubble production as the solute is added in increments.
  2. Compare the rate that each wire is producing bubbles. Is the negative wire more active than the positive?
  3. Decide the "run time" and observe any changes in the solution height.
  4. At the end of the "run time," try to measure by number of mL or by mass of solution what has occured.

Data Sheet

Part 2 Data Table

Grams of solute Observations (conductivity) Concentration (g/mL)

Part 3 Data Table

Initial water level __________________mL = _______________grams

Final water level __________________mL = _______________grams

Detectable change ________________mL = _______________grams

  1. What is the pattern in the circuit in which the charges flowed?

  2. If any breaks occur in the wiring, which type of circuit would be represented?

  3. If all the connections are complete, which type of circuit would be represented?

  4. In the pure water, what was the level of conductivity? (light on or light off)

  5. As the solute was added, what is changed to help charges "travel" in the liquid?

  6. What was the concentration for which the light turned on?

  7. Is the solution changing its state to gas or is it being broken down into component gases?

  8. Compare different solute concentrations for conductivity.