Potassium chlorate

Potassium chlorate (KClO₃) is a strong oxidizing agent that has a wide variety of uses. It is or has been a component of explosives, fireworks, safety matches, and disinfectants. As a high school or college chemistry student, you may have used it to generate oxygen in the lab.

Because it is a strong oxidizer, KClO₃ must be kept from contacting organic matter; reduced inorganic materials such as elemental sulfur, phosphorus; and iodine; and concentrated acids.

The use of KClO₃ in matches dates back to 1826, when English chemist John Walker combined it with antimony(III) sulfide, gum, and starch. When formed into matches, the mixture sometimes (but not always) ignited when struck on sandpaper. Later on, white phosphorus replaced antimony sulfide to make matches more reliable. Eventually, the toxic white phosphorus was superseded by the red allotrope.

Modern safety matches contain no phosphorus; but red phosphorus is embedded in the rough surfaces of matchboxes. Upon striking, the phosphorus ignites, liberating oxygen from the match’s KClO₃, which in turn ignites combustible substances (e.g., sulfur) in the matchhead.

It’s the holiday season, so you will be forgiven if you don’t think about all of this chemistry when you light your Christmas, Hanukkah, or Kwanzaa candles.