Practice: An unknown diprotic acid has an initial concentration of 0.025 M. What is the pH of the solution if pka1 is 3.25 and pKa2 is 6.82?
Diprotic species involve the movement of two acidic hydrogens.
Diprotic Acids and Bases
Concept #1: Diprotic acids can donate two acidic hydrogens and as a result possess two Ka values.
Concept #2: Diprotic bases can accept two acidic hydrogens and as a result possess two Kb values.
Concept #3: With the presence of different forms it becomes essential to know which Ka or Kb value to use.
Diprotic Acids and Bases Calculations
Example #1: 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 0.200 M H2SO3.
Example #2: Determine the pH of 0.080 M Na2S. Hydrosulfuric acid, H2S, contains Ka1 = 1.0 x 10-7 and Ka2 = 9.1 x 10-8.
Example #3: If Ka1 = 4.46 x 10-7 and Ka2 = 4.69 x 10-11 for H2CO3 what is the pH for a 0.15 M solution of NaHCO3?
