|MadSci Network: Chemistry|
Distilled water conduts very little electricity since one needs to have a significant concentration of ions in solution for electricity to flow. In fact water distilling equipments include a measure of "pure" water conductivity as proof of pureness. Distilled water has been stripped of salts that make up the main source of ions. In fact pure water should only containg H2O molecules and H+ and OH- ions. The concentration of these ions is rather low therefore conductivity of pure water is very low. When you add salt, say NaCl, the Na+ and Cl- are able to carry electricity through the water.
You mentioned that even after the addtion of salt to the water in your experiment the light bulb did not light. This may have to do with the positioning of the wires in the liquid. If they are too far apart, the transfer of ions from the water to the wire may not be effecient enough. You may have to bring the wires closer together in the liquid, or even increase the electrode surface area by adding metal plates at the ends. You may also have to adjust the size of your liquid container, stir the liquid, etc., to get the light bulb to light.
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