Ch.9 - Polyprotic Acid-Base EquilibriaWorksheetSee all chapters
All Chapters
Ch.1 - Chemical Measurements
Ch.2 - Tools of the Trade
Ch.3 - Experimental Error
Ch.4 + 5 - Statistics, Quality Assurance and Calibration Methods
Ch.6 - Chemical Equilibrium
Ch.7 - Activity and the Systematic Treatment of Equilibrium
Ch.8 - Monoprotic Acid-Base Equilibria
Ch.9 - Polyprotic Acid-Base Equilibria
Ch.10 - Acid-Base Titrations
Ch.11 - EDTA Titrations
Ch.12 - Advanced Topics in Equilibrium
Ch.13 - Fundamentals of Electrochemistry
Ch.14 - Electrodes and Potentiometry
Ch.15 - Redox Titrations
Ch.16 - Electroanalytical Techniques
Ch.17 - Fundamentals of Spectrophotometry
BONUS: Chemical Kinetics
Diprotic Acids and Bases
Polyprotic Acids and Bases
Diprotic Buffers
Polyprotic Buffers
Principal Species
Isoelectric and Isoionic pH

Diprotic buffers involve the 3 dominant forms of a diprotic acid and its 2 KValues. 

Diprotic Buffers

Concept #1: Monoprotic buffers involve only the weak acid and its conjugate base and therefore only 1 Ka value. 

Concept #2: A diprotic buffer can be approached in a way similar to monoprotic buffers. The key difference is that a diprotic acid has 2  pKa values. 

Monoprotic & Diprotic Buffer Calculations 

Example #1: What is the pH of a solution consisting of 2.5 M potassium dihydrogen phosphite (KH2PO3) and 2.75 M phosphorus acid (H3PO3)? Ka1 = 3.0 x 10-2 and Ka2 = 1.66 x 10-7.  

Example #2: Sulfurous acid, H2SO3, is a major component in the creation of commercial fertilizers. What is the buffer component concentration ratio of a buffer that has a pH of 1.15? Ka1 = 1.39 x 10-2 and Ka2 = 6.73 x 10-8

Practice: Calculate the pH of a solution made by mixing 8.627 g of sodium butanoate in enough 0.452 M butanoic acid, HC4H7O2, to make 250.0 mL of solution. Ka = 1.5 x 10-5