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Why is my salt solution not lighting the bulb?

  1. Feb 14, 2014 #1
    So I have a typical 9volt battery attached to a Christmas light and am attempting to demonstrate the typical "saltwater can conduct electricity" gimmick by showing that the bulb lights when completing the circuit in the solution. I'm racking my brain though and can't figure out why the bulb won't light!

    Some details:
    -The bulb does of course light when the wires are connected outside of solution.
    -I've tried multiple solutions with multiple concentrations (calcium chloride, acids, NaCl, etc) with no luck.
    -However, a conductivity tester also attached to a 9volt battery does show some conductivity in the water.
    -The test battery with the Christmas light does hydrolyze the water (produce bubbles).
    -After attempting the test setup in the solution, I stuck the wires together for a bit outside of the solution. When I did this, one of the wires began to blacken just a tiny little bit. I then stuck the wires back in the solution and a slight yellow precipitate formed. This makes me think there is some coating on the wire (though I don't see why there would be) or that there is some electroplating going on (though this is never really noted in other setups of this experiment I found on the internet). The yellow precipitate I noticed in the NaCl solution.
    -The Christmas lights was just the typical LED green chains you normally see. One of the lights was taken off just by cutting the wires on both ends of a light. Simple simple.

    Any ideas as to what's going on?
  2. jcsd
  3. Feb 14, 2014 #2


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    Staff: Mentor

    Have you measured what is the current flowing through the circuit? My bet is that it is just too low for the light.
  4. Feb 14, 2014 #3
    That may well be it. The light is NOT an LED like I originally posted on second thought (or at least that's not a safe presumption; I don't know how to truly tell the difference visually). But no I didn't measure the current numerically.

    Another detail I forgot, the bulb did light up BRIEFLY in an HCL solution. That does make me think the current's somewhat there just not enough for the bulb.
  5. Feb 14, 2014 #4
    I just remember that the HCl solution that did work briefly was 3 molar. To get that same concentration in table salt, we would have had to add much more than we did. It seems like there just no being enough juice to get through is a reasonable resolution to this unless anyone seems something missing.
  6. Feb 14, 2014 #5


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    Staff: Mentor

    It is not only about concetration, also about ion identity - H+ are are the best.

    Try to increase electrode surface, and try to keep electrodes as close to each other as possible. Conductivity 101.
  7. Feb 20, 2014 #6
    also if your doing salt to water your raitio may be off
  8. Feb 21, 2014 #7
    just guessing
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