5D30.10 - Conduction of Salt Water
Demonstrate that pure water is not a conductor, but an ionic solution is.
Pull out the glass vessel with two long electrodes separated by a piece of plexiglas mounted inside of the vessel. Connect banana cables to the electrodes and connect those in series with the 110-VAC power switch (4-way on/off switch with breakouts). Plug in a 25-W bulb into one of the plugs of the 110-VAC power switch. Provide 300 mL of de-ionized/distilled water and salt. Make sure the insulated banana cable is available for shorting out the electrodes and a long plastic rod is used to stir the salt into the water. Must have a danger sign.
Check that when you short out the electrodes, the 25-W bulb lights up. Make sure the vessel is clean.
First, turn on the 110-VAC power switch and observe nothing happens. Use the insulated banana cable to short out the long electrodes to show that the 25-W bulb will light when the circuit is completed. Then fill the glass vessel with the provided de-ionized/distilled water. The two long electrodes are submerged in the water. The bulb will not light (make sure the vessel is clean). When some salt is added, the bulb will begin to light, indicating that salt dissolved in water can act as a conductor. (Optional in Weiser Hall- thoroughly rinse out the glass chamber after disconnecting it from the power switch to remove all of the salt water. Then fill vessel with classroom water, re-insert into circuit and show how that will work too, tap water is not just water.)
Pure Water - water that has been purified through mechanical filtration or processed to remove imuprities (distillation, deionization, demineralization, etc). Impurities that are removed include inorganic ions, organic compounds, bacteria, endotoxins/nucleases, particulates, gases.
Pure water does not contain any ions, therefore it is not electrically conductive.
If an electrolyte, a substance that produces an electriclaly conducting solution when dissolved in a polar solvant, is added to water then ions are formed and electrical conduction can occur. In this case, we have added table salt NaCl to the pure water, which dissolves into Na+ and Cl- evenly throughout the solution. The water is electrically neutral, but if an electrical potential is applied to such a solution, a current is formed.