Possibly the best pH scale in the world?

I’m sure that everyone remembers using universal indicator to make pretty colours at school and working out the pH of different substances, but how did this most useful chemical tool come into being? Grab a beer and let the story begin!

9th January 1868 was the birthday of the Danish chemist Soren Sørensen who is credited with the development and introduction of the pH scale. The measurement of acidity had long been a difficult process for chemists and mostly relied on measuring the volume of an acid added to another substance. This didn’t account for the amount of dissociation within the solutions produced and any interaction between the ions involved. Sørensen was working at the Carlsberg Institute in Copenhagen and looking especially at how acidity affected proteins in the beer making process. He knew that the shape of protein molecules and enzyme activity was heavily dependent on Hydrogen ion concentration. He needed a quick and easy way of measuring this during the fermentation process to ensure the best conditions to control what was happening to the enzymes and make the best beer (probably!). The Hydrogen ion concentration can vary vastly in solutions and the numbers are difficult to deal with ranging from 1 x 10-14 mol dm-3 (0.00000000000001) to 1 mol dm-3. Sørensen used a negative logarithm scale starting at 0 and ranging to 14. Because it was a negative scale the lower the number the more Hydrogen ions present and therefore the more acidic the solution. Also, for every integer rise in pH the amount of ions decreases by a factor of 10. He used this system and developed indicators and crude meters to help him in his work. It wasn’t until other scientists stumbled across his ideas and saw that it was a much simpler and quicker way of working out concentration of Hydrogen ions that the pH scale was born.

There is much dispute as to where the term ‘pH’ came from. Most believe it comes the meaning of the word ‘power’ of Hydrogen but from which language is uncertain. The German ‘potenz’, the French ‘puissance’ or the Latin ‘pondus’, although the Institute itself was mainly French speaking.

So next time you crack open a beer think of the chemistry it helped develop.