Potassium hydroxide

Potassium hydroxide, KOH, also called caustic potash, is a strong base: it dissolves in water to make a highly alkaline, corrosive solution. It is a close relative of sodium hydroxide (lye) and does many of the same jobs.

Its potassium, oxygen and hydrogen are brought together by electrolysis. Potassium chloride, mined as potash, is dissolved in water and an electric current is passed through it. Chlorine gas forms at one electrode and hydrogen at the other, and the potassium is left in the water as potassium hydroxide, taking its oxygen and hydrogen from the water itself. The solution is concentrated and sold as a liquid, or dried into white flakes or pellets that soak up moisture from the air.

In an alkaline battery it is the electrolyte, which is where the battery gets its name. Mixed into the zinc gel, it carries charged particles between the zinc and the manganese dioxide while electrons travel around through the device. The white crust on a leaking battery forms when it escapes and reacts with carbon dioxide in the air. It is also used to make soft and liquid soaps.