Why measure pH?

• To prepare a buffer solution at a controlled pH level necessary for carrying out chemical or biological experiments in optimal conditions.
• To monitor and direct a chemical reaction and/or the transformation process of food.

e.g. Lactic acidification in cheese factories.

What is pH?

According to Sørensen, pH is defined as the negative logarithm of the concentration of hydronium ions, H₃O⁺, resulting from the dissociation of molecules: When the H₃O⁺ ion concentration changes by a factor of 10, the pH changes by 1 unit.

What is pH neutral?

Not only acids and bases dissociate to form hydronium or hydroxyl ions, pure water also dissociates to form these ions: K_w is the dissociation constant of this reaction, also called the self-ionization of water : The solution is neutral for equal quantities of H₃O⁺ and OH^–.
This is the case when concentrations of [H₃O⁺] and [OH^–] are 10^–7 mol/L, i.e. pH 7.
 

The orders of magnitude of pH