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Science Forum

  1. Subscriber AThousandYoung
    Do ya think?
    24 Aug '08 17:03 / 1 edit
    As a new science teacher I had to do some demonstrations. Here's one.

    I had a metal pan. In it I placed a piece of paper. I soaked the paper in a liquid, dumped out the excess, then lit the paper on fire. A couple seconds later I quickly extinguished the fire, and showed that the paper was completely undamaged. No charred bits at all.

    Explain!
  2. 24 Aug '08 17:34
    You used the wax paper that came with the BLT you had for lunch.
  3. Subscriber AThousandYoung
    Do ya think?
    24 Aug '08 18:02 / 2 edits
    Originally posted by nihilismor
    You used the wax paper that came with the BLT you had for lunch.
    No. That might work though.

    The experiment fails if I do not soak the paper in a liquid first.
  4. 24 Aug '08 18:28
    The liquid is ethanol
  5. 24 Aug '08 18:35
    Originally posted by AThousandYoung
    As a new science teacher I had to do some demonstrations. Here's one.

    I had a metal pan. In it I placed a piece of paper. I soaked the paper in a liquid, dumped out the excess, then lit the paper on fire. A couple seconds later I quickly extinguished the fire, and showed that the paper was completely undamaged. No charred bits at all.

    Explain!
    You were drinking heavily before the demonstration.
  6. Subscriber AThousandYoung
    Do ya think?
    24 Aug '08 18:45
    Originally posted by darkbishop28
    The liquid is ethanol
    Isopropyl alcohol actually.

    But not only isopropyl alcohol. There's something mixed in that might help protect the paper.
  7. 24 Aug '08 19:09
    Originally posted by AThousandYoung
    Isopropyl alcohol actually.

    But not only isopropyl alcohol. There's something mixed in that might help protect the paper.
    I was close
  8. 24 Aug '08 19:57
    Originally posted by AThousandYoung
    As a new science teacher I had to do some demonstrations. Here's one.

    I had a metal pan. In it I placed a piece of paper. I soaked the paper in a liquid, dumped out the excess, then lit the paper on fire. A couple seconds later I quickly extinguished the fire, and showed that the paper was completely undamaged. No charred bits at all.

    Explain!
    You stood behind your table and because the class was far enough from you, you could fool them into believing that it really was paper. It was actually a painted aluminum plate which you soaked in fuel.

    And of course it wouldn't have worked, if you hadn't soaked it in fuel. Aluminum doesn't burn that easily. Dooh!
  9. 24 Aug '08 20:24
    Originally posted by AThousandYoung
    Isopropyl alcohol actually.

    But not only isopropyl alcohol. There's something mixed in that might help protect the paper.
    is it alcohol and water?
  10. Standard member forkedknight
    Defend the Universe
    24 Aug '08 21:31
    It all depends on how much liquid is involved. If you put enough gasoline for the paper to be submerged, you could do the same thing.
  11. 25 Aug '08 03:33
    Originally posted by AThousandYoung
    As a new science teacher I had to do some demonstrations. Here's one.

    I had a metal pan. In it I placed a piece of paper. I soaked the paper in a liquid, dumped out the excess, then lit the paper on fire. A couple seconds later I quickly extinguished the fire, and showed that the paper was completely undamaged. No charred bits at all.

    Explain!
    I think you soaked the paper in water previous to the experiment, then put it in the pan with isopropanol until the paper had just a thin film of isopropanol on it.

    The paper would still be soaked with water and so would not burn but the isopropanol would burn.

    ?

  12. Subscriber AThousandYoung
    Do ya think?
    25 Aug '08 04:49
    Originally posted by darkbishop28
    is it alcohol and water?
    Yes.
  13. Subscriber AThousandYoung
    Do ya think?
    25 Aug '08 04:50
    Originally posted by mlprior
    I think you soaked the paper in water previous to the experiment, then put it in the pan with isopropanol until the paper had just a thin film of isopropanol on it.

    The paper would still be soaked with water and so would not burn but the isopropanol would burn.

    ?

    You got the general idea.
  14. Subscriber coquette
    Already mated
    25 Aug '08 04:56
    Solids don't burn. They vaporize first, then the vapors (gases) burn.

    The liquid vaporizes before the solid (paper).

    Only the liquid was burning, even though it looked as though the paper was burning.

    The paper was a catalyst (a wick, as on a candle).

    What kind of a science teacher does a cool demonstration and doesn't explain what the point was? Or, was that your assignment, to come up with the explanation? Did we help you cheat?
  15. Subscriber AThousandYoung
    Do ya think?
    25 Aug '08 05:19 / 4 edits
    Originally posted by coquette
    Solids don't burn. They vaporize first, then the vapors (gases) burn.

    The liquid vaporizes before the solid (paper).

    Only the liquid was burning, even though it looked as though the paper was burning.

    The paper was a catalyst (a wick, as on a candle).

    What kind of a science teacher does a cool demonstration and doesn't explain what the point was? Or, was that your assignment, to come up with the explanation? Did we help you cheat?
    First of all, I didn't do this one because it made me uncomfortable (open flame ) and I only had 20 minutes. It was just one of a bag of tricks and I didn't have time for it. I did an oil and water demonstration (homemade lava lamp), a salt and soda demonstration, and vinegar and baking soda. I had more planned but I only had 20 mins and I didn't bring my lighter that day anyway.

    If I had done it, I would have explained it...after I asked my students to try to explain it to me!

    Also unused were the "put out the candle with a glass" and a "relight the candle by igniting the smoke" demos, the second of which I still haven't even tried once.

    It was a demo for orientation, that's all. The students didn't need to take notes or anything.