pH : Definition, Measurement and Examples

🏾 Contents :

â—‰ What does pH mean ?

The decrease of one pH unit implies that the acidity is multiplied by a factor of 10. Thus:

  • Water with a pH of 6 is ten times more acidic than water with a pH of 7.
  • Water with a pH of 5 is 100 times more acidic than water with a pH of 7.

â—‰ History : weight of hydrogen or hydrogen potential?

In 19092, the Danish chemist Søren Sorensen , who worked on the effects of the concentrations of a few ions on proteins during the processes beer making, notices the importance of hydrogen ions and decides to introduce the concept of pH.

â—‰ pH scale

The pH scale is used to classify solutions in terms of acidity or basicity (alkalinity). This scale is based on the balance between hydrogen ions [H+] and hydroxyl ions [OH-] :

  • If the concentration of H+ is higher than that of OH-, the material is acidic; that is, the pH value is less than 7.
  • If the OH concentration is greater than its H+, the material is basic, with a pH value greater than 7.
  • If equal numbers of H+ and OH ions are present, the material is neutral, with a pH of 7.

The pH scale is often said to run from 0 to 14, and most solutions fall within this range. However, very strong acids can have a negative pH, while very strong bases can have a pH above 14.

Table 1 : Average pH of common solutions
Substance pH range Type
Battery acid <1 Acid
Stomach acid 1.0 - 1.5
Vinegar 2.5
Orange juice 3.3 - 4.2
Black coffee 5 - 5.03
Milk 6.5 - 6.8
Pure water at 25°C 7 Neutral
Sea water 7.5 - 8.4 Base
Ammonia 11.0 - 11.5
Bleach 12.5
Detergent 13.0 - 13.6

â—‰ How to measure pH?

Le pH peut être mesuré électroniquement ou visuellement. Il existe deux principales méthodes couramment utilisées :

â—‰ What is the best water pH ?

Water with a very low or high pH can be a sign of chemical pollution or heavy metals.

The best drinking water pH is right in the middle at 7. The United States Environmental Protection Agency recommends that the pH level of water sources be at a level of measurement pH between 6.5 and 8.5.

â—‰ Urinary pH

Normal urinary pH is slightly acidic, common urine pH value is 6.0-7.5 for most people, but normal range is 4.5-8 ,0.


  1. khanacademy - Acids, bases, pH, and buffers
  2. The pH Scale
  3. atago - Qu'est-ce que le pH ?
  4. thoughtco - pH Definition and Equation in Chemistry
  5. reagent - what is ph scale ?
  6. Acids, Bases, & the pH Scale
  7. Michael J. Bono et al - Urinary Tract Infection
  8. pmel - A primer on pH
  9. Erich K. Springer - pH Measurement Guide
  10. Gilbert Bilodeau - Le pH, c'est pas compliqué !
  11. EPA - Drinking Water Regulations and Contaminants