Element number 19 in our International Year of the Periodic Table series is potassium – used to make soaps, and also the reason that bananas are radioactive.

Potassium hydroxide is commonly used to make soaps. There’s some detail on the soap-making process in this graphic comparing soaps and body wash. It’s most commonly used to make liquid soaps, with sodium hydroxide being used for solid soaps. Another industrial use of potassium is in fertilisers, which is needed by plants for flowering and fruiting.

In our bodies, potassium ions play important roles. They regulate blood pressure and the transmission of nerve impulses, and are required for normal cell function.

An rare isotope of potassium, potassium-40, is radioactive, and is the largest source of radioactivity in animals and humans. It also makes bananas very slightly radioactive, leading to the informal banana equivalent dose for measuring radiation exposure. Decay of potassium-40 to argon is responsible for the abundance of argon in our atmosphere (1%).

Remember, you can keep track of all of the previous entries in this series on the site here, or on the Royal Society of Chemistry’s dedicated page.