Historical figure · Pearson Edexcel International GCSE revision on Incandio

Søren Sørensen

Who Gave Acidity A Number · Chemist · 1868–1939

The Carlsberg brewery chemist who invented the pH scale in 1909, because studying enzymes was impossible without a way to measure acidity.

Defend these ideas against Sørensen

Incandio is a free revision platform for the Pearson Edexcel International GCSE, and on it a topic counts as mastered only once you have learned it, proved it in questions, taught it back and defended it against the person with the strongest claim on it. Søren Sørensen is that person for one topic on the course:

• Enzymes and pH — Biology

Who was Sørensen?

Søren Peter Lauritz Sørensen was born in 1868, the son of a farmer at Havrebjerg, and came to chemistry after starting out in medicine. In 1901 he became director of the chemical department of the Carlsberg Laboratory in Copenhagen — a research institution endowed by the brewery's founder on the condition that its results be published rather than kept. His problem there was entirely practical, and it was defeating everyone who met it: enzymes and proteins in brewing behaved differently from one preparation to the next, the difference plainly had something to do with acidity, and there was no way to say how acidic anything was. Chemists described solutions as weakly or strongly acid, which could not be compared between two laboratories and settled no argument. In 1909 Sørensen gave the quantity a number. He defined it from the concentration of hydrogen ions and took its negative logarithm, so that a range spanning many powers of ten became a scale running from about 1 to 14, and he called it the hydrogen-ion exponent — pH. He set out how to measure it, with a hydrogen electrode for precision and with coloured indicators for those who had no electrode, and he described the buffer solutions that hold it steady while an experiment runs. He then used the new scale to establish that enzyme activity depends sharply on acidity, each enzyme having a value at which it works best. He worked for the rest of his career on proteins and their crystallisation, much of it with his wife Margrethe Høyrup Sørensen, herself a chemist. He died in 1939.

Major achievements

• Defined the pH scale in 1909 and gave acidity a measurable number
• Established the hydrogen-electrode and indicator methods of measuring it
• Described the buffer solutions that hold pH steady during an experiment
• Showed that enzyme activity depends sharply on pH, with an optimum for each enzyme
• Developed the formol titration for amino-acid analysis

Life in brief

• 1868 — Born at Havrebjerg: A farmer's son; begins in medicine before turning to chemistry.
• 1901 — Carlsberg Laboratory: Becomes director of its chemical department.
• 1909 — pH defined: The hydrogen-ion exponent, with electrode and indicator methods and buffer solutions.
• 1912 — Enzymes and acidity: Uses the new scale to establish the dependence of enzyme activity on pH.
• 1917 — Protein chemistry: Turns to proteins and their crystallisation, with Margrethe Høyrup Sørensen.
• 1939 — Dies in Copenhagen: With his scale in every laboratory on earth.

Explore the life of Sørensen — five chapters

1. A Brewery That Had to Publish — An unusual institution, and an unusual condition
2. Weakly Acid — A description that settles nothing
3. Take the Logarithm — pH, 1909
4. Each Enzyme Has Its Own Best Value — Using the new scale on the original problem
5. On Every Bottle in the World — What an invented quantity is worth

Read the five-chapter life of Søren Sørensen →

Where Sørensen appears in your course

Søren Sørensen has a genuine claim on 1 lesson of the Pearson Edexcel International GCSE science course built into Incandio:

• Enzymes and pH — Biology: The pH scale on the x-axis of your graph was invented in 1909 by Sørensen, at the Carlsberg brewery laboratory, and it was invented for exactly this problem: he was studying how enzymes behave in brewing, found that acidity changed everything, and had no way of stating how acidic anything was. This lesson is the reason the scale exists.

Begin

• Start a conversation with Sørensen — a dramatised, historically grounded AI portrayal
• Read the Historical Brief
• Explore the life of Sørensen — five chapters
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