As you know, dollar bills are made out of
paper. For something to burn, its temperature
needs to reach a point known as its ignition
temperature. If you soaked a dollar bill in a
pure alcohol solution and then lit it, I am pretty
sure that it would burn the dollar bill.
what happens if the
alcohol is diluted in water.
I think the "classic" science demo is to mix
a 50:50 solution of alcohol and water together,
and then soak the bill in it. When you try to
light it on fire, you should see a flame, but then
it will eventually go out and the dollar is still
fine (wet and warmer, but not burnt). The key to
this is the ability of water to absorb a large
amount of heat. When you ignite the
alcohol/water-soaked bill, only the alcohol will
burn. The water absorbs the released heat, and
thus keeps the temperature of the water-bill
relatively cool. Now, if there isn't enough water
present, the burning alcohol could heat the water
until the water evaporates, in which case the heat
from the burning alcohol could then heat the bill
and cause it to ignite.
If you can experiment with this, you could
try mixing differing amounts of alcohol and water
together to find out at what concentrations the
bill (here I'd suggest just using paper!) will
ignite. Additionally, you could also experiment
with different types of alcohol as well.
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