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What happens when you put inert electrodes @ 220V/50Hz in tap water?

  1. Apr 3, 2008 #1
    Anyway ... a long long time ago, my father told me a story how when he was in college, they used to heat water just by putting putting 2 inert electrodes (graphite) in tap water and it would instantly (in a few seconds) boil.

    He said they used to make coffee and pasta that way :)

    Now that I'm in college (and have been attending a Physical Chemistry class recently) I've been thinking about the mechanics of such heating method.

    Anyway, I figure that due to a fast change in polarity (50 times per second) the water heats up due to molecular friction of solvatation shell (I don't know what's the term in English) as it passes through non-ionized water.

    Am I even going in the right direction? :)
    Does it even happen?

    I'm too much of a pussy to play with 220V since I got electrocuted.
     
  2. jcsd
  3. Apr 3, 2008 #2

    mgb_phys

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    Tap water is far from non-ionic it has a conductivity of 0.005 – 0.05 S/m depending on the minerals in your area.
     
  4. Apr 3, 2008 #3
    But when I was young, I did the same thing only to find that a lot of hydrogen and oxygen are generated, compared with heat. That's dangerous!
     
  5. Apr 4, 2008 #4
    I don't think the changing polarity has anything to do with it. A sinusoidal voltage of peak X should heat the water as much as a constant voltage equal to the sinusoid's root-mean-square value, X/(square root of 2).

    Ionic compounds dissolved in the water are the biggest factor. My own well water contains a lot of calcium carbonate. Search key word 'electrolyte'.

    Whether there would be small effect for pure water, that's beyond my knowledge.
     
  6. Apr 6, 2008 #5

    rbj

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    i might think the circuit breakers would trip before anyone gets to virtually "instantaneously" heat up their water.

    i heard, when i lived in Portland Maine, that the city tap water came from Sebago Lake and was so low in electrolytes, that people used it in car batteries. but anywhere else, tap water conducts pretty good.

    if it was a serious power main that could deliver hundreds of amperes before tripping a breaker, then i might imagine putting those electrodes into a cup of tap water would heat it to boil pretty damn fast. fast enough that you might get it sorta exploding out of the cup.
     
  7. Apr 6, 2008 #6

    rbj

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    you need to set it up in a "controlled experiment". 220V is the normal single-phase service in your houses in Europe, no? (here, in North America, it's 110V. 220V is what the electric stove or clothes dryer or sometimes the air conditioner run on.) i imigine you guys get more electrocuted kids dicking around with wires and other metal things we stick into wall outlets.
     
  8. Apr 7, 2008 #7

    Shooting Star

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    It does. I had a small one when I was a kid. It's basically two round metal plates with holes, separated by a small distance and held together by a kind of yoyo whose inside stem is passing through the holes. The main problem is that the live wire which is connected to one of the plates fuses after just a few minutes.

    After a few years, I took two razor blades, and tied them to very thick aluminium wires, and dipped them in a bucket about an inch or so apart. It worked fine. It is really fast.
    That's because you were using DC. It should be used with AC.
    That's right, but as mentioned above, you'll get Hydrogen and Oxygen. I tried it with DC, but such a lot bubbles started to come out that I got scared and took it out. Remember, I was a kid then...It also could have been partly water vapour, because the water gets very hot if the separation is small, and starts to boil.

    Somehow, I never tried it again. Guess I grew old...
    If you use the right materials and adjust the gap properly, nothing should happen. It's quite safe (after a few trials and errors).
     
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