Sunday, November 7, 2010

Science Projects & Models

This is a neat 'magic trick' that illustrates the process of combustion, the flammability of alcohol, and the special qualities of the material used to make currency.
Scientific Concept behind Burning Money
A combustion reaction occurs between alcohol and oxygen, producing heat and light (energy) and carbon dioxide and water.
C2H5OH + 4 O2 -> 2 CO2 + 3 H2O + energy
When the bill is soaked an alcohol-water solution, the alcohol has a high vapor pressure and is mainly on the outside of the material (a bill is more like fabric than paper, which is nice, if you've ever accidentally washed one). When the bill is lit, the alcohol is what actually burns. The temperature at which the alcohol burns is not high enough to evaporate the water, which has a high specific heat, so the bill remains wet and isn't able to catch fire on its own. After the alcohol has burned, the flame goes out, leaving a slightly damp dollar bill.
Here's what you need to do the demonstration...

Here is what you need to perform the burning money demonstration:
  • dollar bill (higher denomination if you're brave)
  • tongs
  • matches or a lighter 
  • flame
  • solution of 50% alcohol and 50% water (you can mix 95% alcohol with water in a 1:1 ratio, if desired)

salt (or one of these chemicals if you want a colored Flame Colorants

Lithium Chloride
Strontium Chloride
Calcium Chloride (a bleaching powder)
Sodium Chloride (table salt)
or Sodium Carbonate
Yellowish Green
Copper Sulfate or Boric Acid
Copper Chloride
3 parts Potassium Sulfate
1 part Potassium Nitrate (saltpeter)
Potassium Chloride
Magnesium Sulfate (Epsom salts)

Have you gathered your materials? Let's burn money...
  1. Prepare the alcohol and water solution. You can mix 50 ml of water with 50 ml of 95-100% alcohol.
  2. Add a pinch salt or other colorant to the alcohol/water solution, to help produce a visible flame.
  3. Soak a dollar bill in the alcohol/water solution so that it is thoroughly wet.
  4. Use tongs to pick up the bill. Allow any excess liquid to drain. Move the damp bill away from the alcohol-water solution.
  5. Light the bill on fire and allow it to burn until the flame goes out.

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