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How To Perform the Instant Fire Chemistry Demonstration

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Potassium chlorate and sugar burn to produce a purple flame.

You can ignite a mixture of potassium chlorate and sugar with a flame or by adding a few drops of sulfuric acid. The reaction is very energetic and produces purple fire.

Skatebiker, public domain

Potassium chlorate and ordinary table sugar are combined. When a drop of sulfuric acid is added, a reaction is catalyzed which produces heat, an amazing bright/tall purple flame, and a lot of smoke.

Difficulty: Easy

Time Required: minutes

Here's How:

  1. Mix equal parts potassium chlorate and table sugar (sucrose) in a small glass jar or test tube. Choose a container you don't value, as the demonstration will probably cause it to shatter.
  2. Place the mixture in a fume hood and equip lab safety gear (which you should be wearing anyway). To initiate the reaction, carefully add a drop or two of sulfuric acid to the powdered mixture. The mixture will burst into into a tall purple flame, accompanied by heat and a lot of smoke.
  3. How it works: potassium chlorate (KClO3) is a powerful oxidizer, used in matches and fireworks. Sucrose is an easy-to-oxidize energy source. When sulfuric acid is introduced, potassium chlorate decomposes to produce oxygen:

    2KClO3(s) + heat —> 2KCl(s) + 3O2(g)

    The sugar burns in the presence of oxygen. The flame is purple from the heating of the potassium (similar to a flame test).

Tips:

  1. Perform this demonstration in a fume hood, as a considerable quantity of smoke will be produced. Alternatively, perform this demonstration outdoors.
  2. Granulated table sugar is preferable to powdered sugar which is in turn preferable to reagent grade sucrose. The powdered sugar is capable of smothering the fire, while the granules of the reagent-grade sucrose may be too large to support a good reaction.
  3. Follow proper safety precautions. Do not store the potassium chlorate and sugar mixture, as it can react spontaneously. Use care when removing the potassium chlorate from its container, to avoid sparking, which can ignite the container. Wear the usual protective gear when performing this reaction (goggles, lab coat, etc.).
  4. The 'Dancing Gummi Bear' is a variation on this demonstration. Here, a small quantity of potassium chlorate is carefully heated in a large test tube, clamped to a ring stand over a flame, until it has melted. A Gummi Bear candy is added to the container, resulting in a vigorous reaction. The bear dances amidst bright purple flames.

What You Need:

  • potassium chlorate
  • powdered (confectioners) sugar or table sugar (sucrose)
  • sulfuric acid
  • small glass jar or test tube

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