Diprotic Acids

A diprotic acid is an acid that can donate two hydronium ions (H+). 

Diprotic Acids

Since a diprotic acid has two acidic hydrogens it would have 2 equilibrium equations. 

The diprotic bases would also have 2 equilibrium equations. 

Concept: As a result of these equations for diprotic acids and bases the relationship between Ka and Kb can be established. 


Concept: Sulfurous acid, H2SO3, represents a diprotic acid with a Ka1 = 1.6 x 10-2 and Ka2 = 4.6 x 10-5. Calculate the pH and concentrations of H2SO3, HSO3 and SO32– when given 0.250 M H2SO3


Concept: Determine the pH of 0.115 M Na2S. Hydrosulfuric acid, H2S, contains Ka1 = 1.0 x 10-7 and Ka2 = 9.1 x 10-8.