By Vance Bennett
The conventional wisdom says “pH” stands for “Power” of hydrogen or “Potential” of hydrogen. Is this correct? Maybe not.
If you take a class in basic chemistry as a part of your hazmat training you will surely hear the instructor pass on that pearl of wisdom. They will often say it in solemn tones to emphasize the importance of this concept.
There’s only one problem, the guy who invented the idea of pH never said what the letter stood for. He also never used the term “power of hydrogen” or any similar term.
Also Read: Hazmat History
The term “pH” was developed by Danish research chemist Søren Peter Lauritz Sørensen. He was the director of the Carlsberg Research Laboratory in Copenhagen, Denmark from 1901 to 1938. While there, he studied the effect of ion concentration in the analysis of proteins. At that time, there were two primary methods of determining whether a substance was acidic or basic: a color change test and electrometric.
Sørensen refined these techniques and established a method of expressing the relative hydrogen ion activity. He called this the “pH” scale. His scale went from 0 to 14 — 7 was neutral, 0 was acidic and 14 was basic. This is the scale used to this day.
The question often asked is: What do those letters mean?
Various people have put forth various explanations. All are sincere and all are convinced of the conventional wisdom regarding this term. The only person who didn’t say anything about what these letters meant was Sørensen.
The most common explanation is that the “p” stands for “power.” This is highly unlikely since that is English word and Sørensen didn’t publish in English. None of his papers used the phrase “power of hydrogen” and none of his associates were known to use that term in any of their published papers.
Sørensen primarily published in German, he spoke Danish and the business of his lab was conducted in French. All three languages have a word that corresponds to “power” and all start with the letter “p.” None of Sørensen’s papers made any mention of associating the letter “p” with those terms.
So, did he imply in any way what the term meant? Yes, but not in the way people commonly assume.
The test Sørensen employed used two electrodes in the solutions he tested. He labelled one solution the “q” solution and the other the “p” solution. These two letters are commonly used to represent variables in an equation. The are frequently paired in mathematics.
It appears that Sørensen simply made an arbitrary choice about the two letters and he didn’t give them any further significance. It was simply a matter of typographic convenience.
About the Author
Vance Bennett is retired from California Specialized Training Institute, the training branch of the Governor’s Office of Emergency Services. During his 30 years at CSTI he was an Emergency Management coordinator and instructor in the Hazardous Materials Section. He was the course manager for several CSTI courses including Hazmat Incident Commander, First Responder Operations and CSTI Instructor Certification. As the CSTI representative to the FIRESCOPE Hazardous Materials Subcommittee, he helped develop hazmat team typing and equipment standards for California hazmat teams. Vance was also a regular presenter at the Hazmat Continuing Challenge Workshop.
Prior to coming to work for CSTI, he was on active duty in the U. S. Coast Guard specializing in marine safety and pollution response. During that time he was involved in responses to hazmat incidents and oil spills including the EXXON Valdez and American Trader spills. He served in a variety of USCG units including the Pacific Strike Team before retiring in 2009.