The concept pH

Measure acidity or alkalinity

The pH system is an international way to indicate the acidity or alkalinity (= strength of a base). This scale ranges from 0 to 14.

Pure water is neutral with a pH value of 7. The lower the pH value, the more acidic the solution. The higher the pH, the more alkaline the product.

Practical examples of pH values

Some examples of pH values:

  • Sulfuric acid: pH 1
  • Citric acid: pH 2
  • Acetic acid: pH 3
  • Water: pH 7
  • Ammonia: pH 11
  • Sodium: pH 13

Looking at these examples, it appears that the difference between the sulfuric acid and the citric acid is the same as between the citric acid and acetic acid. Nothing could be further from the truth, since the pH scale is logarithmic.

For example, sulfuric acid is a strong acid, while the two other are weak acids.

The same is true for the higher values. Sodium hydroxide is a much stronger base than ammonia.

The pH scale can be shown graphically as in the picture below:

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