Flame test

Flame tests are used to determine the composition of unknown salts. When presented with a beaker of an unknown solution or solid of which you need to dispose, it's generally a Good Thing to know whether it can go down the drain or whether it needs to go into a waste container. In a flame test, the substances being tested will actually change the color of the flame, depending on (of course) the substance. This is a result of emission spectra which in turn are a result of electrons returning from an excited state to their ground state.

There are a number of ways one could perform a flame test. Among those, these are three:

• Scrape a tiny, tiny bit (you might be surprised at how little you need) from the solid with a long piece of wire wrapped around a glass stirring rod, using the glass as a handle. Hold the wire end over a Bunsen burner flame. (This is probably not a good idea with nitrate salts. They'll blow up on you.)
• Mix a little bit of the solution with a little bit of methyl alcohol in a petri dish. (You can do this with a solid, too. Just add water.) Ignite the mixture with a match or other suitable igniting device. The petri dish's lid makes for an excellent instrument to extinguish the fire.
• Mix some of the solution with a good amount of methyl alcohol in a 250mL Erlenmeyer flask. (Again, this works with solids, too. Just add water.) Now get a two-hole stopper and put it in the flask. Get some glass tubing to fit the stopper and stick both pieces in. One piece should have an end under the surface of the solution while the other should be dry. Here's a drawing of what it should look like:
  

  <- from gas   to burner ->
  ___________   ___________ 
  _________  | |  _________
           | | | |
           | | | |
           | | | |
           | | | |
           |_|_|_|
          || | | ||
          || | | ||
          || | | ||
          || | | ||
          || | | ||
         / | | | | \
        /  | |      \
       /___|_|_______\
      /    | |        \
     /     | |         \
    /  methanol/unknown \
   /       solution      \
  {_______________________}
  

  
  Connect the gas and burner (Meker or Bunsen--try both; your results may vary) to the apparatus. Turn the gas on and ignite.

Now while all the pretty colors are fine and dandy, wouldn't it be nice if you could make something of them? Here's a list of the substances which provide a useful flame test:

• Lithium - red (my favorite)
• Boron - green (boric acid, H₃BO₃, is a good substance to demo using the Erlenmeyer flask method)
• Sodium - orange
• Calcium - red
• Strontium - red
• Barium - green
• Copper - blue-green
• Arsenic - blue
• Selenium - blue
• Indium - blue
• Potassium - violet
• Rubidium - violet
• Cesium - violet

Fireworks are a good example of where these metals and metal ions are useful. For example, copper (II) chloride, CuCl₂, is used in fireworks to create blue showers of sparks.

Another procedure involves placing a sample in a crucible, covering it to prevent loss, and mounting it with a ringstand directly in the flame of a bunsen burner, the idea being that whatever can be oxidized, will be, and that the remaining material is chemically inert. As a general rule of thumb, it is assumed that these remains cannot be metabolized, should the sample be consumed, and will either pass through the system, or stick to fatty tissues. It's a good place to begin a qualitative analysis in a biological or environmental context.

At a Science Olympiad meeting, we set up one of the above tests to see if the store brand cheeseballs that we'd been eating were actually digestible. After ten to fifteen minutes over a full flame, the cheeseballs produced a thick black soot, coated in a tarlike liquid. Further flaming could not dispose of either, and it was concluded that at least 90% of cheeseball mass cannot be broken down by any of the body's systems, and that each of us now has several ounces of unidentified crud stuck to his liver.