Did you know that you can use salt water to make a light bulb shine? It sounds crazy, but it’s true! This is because salt water is a good conductor of electricity.
Salt molecules are made of sodium ions and chlorine ions. (An ion is an atom that has an electrical charge because it has either gained or lost an electron.) When you put salt in water, the water molecules pull the sodium and chlorine ions apart so they are floating freely. These ions are what carry electricity through water. Watch it work in this project! (Adult supervision recommended.)
What You Need:
- Cup or beaker
- Masking tape
- Insulated copper wire
- 9-volt battery
- Aluminum foil
- 3.7-volt light bulb in socket (or buzzer)
- Tongue depressors (or popsicle sticks)
What You Do:
1. Wrap two tongue depressors in aluminum foil. These will be your electrodes.
2. Cut three 6-inch pieces of insulated copper wire and strip a half-inch of insulation off each end.
3. Connect one end of a wire to the positive terminal of the battery – hold it in place with masking tape. (If you are using a battery cap, connect it to the red wire.) Connect the other end of the wire to the light bulb socket. (Just wrap the wire around the bottom of the bulb, if you don’t have a socket. You may have to secure it with tape.)
4. Take the second piece of wire and connect the light bulb socket with one of the electrodes. Use masking tape to stick the bare end of the wire on the aluminum foil near the top the electrode.
5. Use the third piece of wire to connect the negative terminal of the battery with the other electrode.
6. Test out your circuit by touching the two electrodes together. This should complete the circuit and allow electricity to flow from one terminal of the battery to the other, lighting up the light bulb in the process. If the bulb doesn’t light up, check your wire connections to make sure they are all secure and then try again.
Testing the circuit in water
1. Pour 1 cup water into a cup or beaker. (If you have distilled water, that will work best.)
2. Put the two electrodes in the cup, but don’t let them touch each other. What happens to the light bulb?
3. Remove the electrodes from the cup and then stir in a teaspoon of salt until it dissolves. Put the electrodes in the salt water without touching them together. Watch the light bulb.
The light bulb lit up because the sodium and chorine ions conducted the electricity from one electrode to the other. This completed the circuit, causing the light bulb to shine. Try adding more salt and see if the light bulb shines brighter. Use a buzzer instead of a light bulb and see if more or less salt in the water makes the buzzer ring louder or softer.
Try this solar distillation project to get fresh water out of salt water and then use your saltwater circuit to test the water you distill! Fresh water won’t conduct electricity as well as salt water.