water-reactive potassium26 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.



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