What is pH?

What is pH?

pH is a widespread scale that is used in chemistry throughout the world. A pH scale is used to measure if a water-based solution is acidic, basic or neutral. pH has a scale from 0 to 14, where 7 is neutral. Any substance with a pH level below 7 is considered to be acidic. Any substance with a pH level above 7 is considered to be basic. A water-based substance with a pH level of 7 is neutral.

Measuring pH is a very important step in the analysis of water-based solutions. pH measurement is often the first step in water analysis and a key factor in industries such as: drinking water, pool water, hydroponics, fish-farms, pollution, food, brewing…

PH is measured with a pH meter, pH electrode or pH testing strips. Find out more information on how to measure pH here.

What does pH stand for?

It is widely accepted that pH stands for the Power or Potential of Hydrogen. It is academically accepted that Søren Peter Lauritz Sørensen, a Danish biochemist was the first to describe the word in literature around the beginning of the 20th century.

Where the p of pH stands for Power or Potential and the H stands for the chemical element of Hydrogen. There reason why there is confusion is because in German the p stands for Potentz or Potential and in French it means Pouvoir, which Power. Regardless of who is right, both terms mean the same, and so the word pH has been used to describe if a water-based substance is acidic or basic.

Søren Peder Lauritz Sørensen was born in Denmark, in the town of Havrebjerg in 1868 and studied at the university of Copenhagen. After he graduated, he found a job working for the laboratory of the Carlsberg brewing factory where helped defining all the chemical processes involved in brewing beer. During his work at the laboratory in the year 1909, he defined the pH scale as a scientific method to measure the pH level of a water-based substance. To this day we still use the same pH scale to measure the pH level.

The pH Scale

The most commonly used pH scale goes from 0 to 14. A water-based substance with a pH of 7 is considered neutral, it is neither Acidic nor Basic. Any Substance with a pH between 0 and 7 is considered to be an Acid, the closer to 0, the more Acidic a substance becomes. A substance with a pH level between 7 and 14 is considered to be Basic, the closer to 14, the more Basic a substance becomes.

pH Scale what is pH how to measure pH pool aquarium spa lab


PH is a measured with a logarithmic scale. Each number represents a 10-fold change in the acidity/basicness of the water. For example: water with a pH of 4 is ten times more acidic than water having a pH of five. Water with a pH of 3 is 100 times more acidic than water with a pH of 5, water with a pH of 2 is 1000 more acidic than water with a pH of 5. Do you see the importance of a measuring pH accurately now?


Popular examples of substances with a low pH are Coca-Cola, sparkling water and red wine. Pure water has a neutral pH of 7. And Baking soda and bleach have a high pH level.

The equation of pH

pH=-log[H+] concentration,
which reads as:
The pH level is equal to minus the log of the H+ concentration.
For example when the H+ concentration is very low, at about 0.0000001M, then the pH value is
pH= -log[.0000001] which is the same as -log[1 X 10-7]
the term log[1 X 10-7] = -7
- (-7) = 7