"Today in chemistry history" graphic for 9th January, marking Danish chemist Søren Sørensen's birthday in 1868 and his invention of the pH scale. Sørensen came up with the pH scale to measure hydrogen ion concentrations in solutions while working at the Carlsberg research lab in Copenhagen. The pH scale runs from 0 to 14 and is a way of measuring how acidic or alkaline a solution is. It’s a logarithmic scale, so a change of one represents a ten times increase or decrease in acidity or alkalinity. A neutral solution has an equal concentration of hydrogen and hydroxide ions; this is usually at pH 7, but can vary slightly depending on temperature.
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On this day (9th January) in 1868, Danish chemist Søren Sørensen was born. He’s best known for developing the pH scale, which we’ve likely all encountered, to measure the acidity or alkalinity of solutions. This graphic gives a brief overview of the pH scale and what it means.

Sørensen was working at the Carlsberg Research Laboratory — yes, that’s Carlsberg, the beer — when he came up with the pH scale in 1909. It resulted from his work on proteins, during which he noticed that the concentration of hydrogen ions had particularly significant effects. The pH scale gave a simple way of expressing hydrogen ion concentration, and has become a staple of school chemistry.

For more detail on the scale, there’s this previous post.