Recently Added Formulas in Chemistry

· Hydrolysis
· Ionization
· pH scale
· Acid-base Reaction
· Strength of Acid and bases

Additional Formulas

· Acid and Base
· Bronsted/Lowry theory
· Strength of Acid and bases
· Acid-base Reaction
· pH scale
· Buffers
· Ionization
· Hydrolysis

Current Location > Formulas in Chemistry > Acid and Bases > pH scale

pH scale

Acidity and basicity of a solution is measured by pH. pH is defines as the negative logarithm (base 10) of the molar concentration of dissolved hydronium ions [H₃O⁺].

pH = -log₁₀[H⁺]

H2O ↔ H⁺ + OH^-

The dissociation constant:

.

Here [H2O] is constant, So, K [H2O] = [H⁺] [OH^-] = Kw

Kw is an ionic product of water and its value is 1x10^-14 at 25°C.

[H⁺] [OH^-] = 1x10^-14

Pure water dissociate completely and has equal concentration. Thus [H⁺] = [OH^-]

[H⁺] [H⁺] = 1x10^-14
[H⁺] = 10^-7
pH = 7

Thus, pure water is a neutral solution having pH equal to 7.0.

Acidic soution pH < 7
Basic solution pH > 7