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26
March 2003
.This is the color of a potassium fire. I've usually
seen it, quite faintly, when doing "flame tests" with potassium
salts, like potassium chloride (KCl). There are a few ways to do flame
tests. One is by holding crystalline KCl directly in a Bunsen burner flame
with a small wire. Another is to pour methanol over a sample of solid
KCl in a watch glass, then light the methanol.
The experiment shown here is much more dramatic. I dropped
a small piece of solid potassium metal (K) into an Erlenmeyer flask filled
with 10-20 milliliters of water. Potassium burns spontaneously, and quite
violently, when it's exposed to water. The violet flame lasts only for
a split second as the metal melts, skits around on the water's surface,
and produces occasional popping and hissing sounds as it generates hydrogen
gas in the reaction K + H2O KOH + H2.
DWL
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