Clutch Prep is now a part of Pearson
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

Polyprotic species involve the movement of 3 or more acidic hydrogens. 

Polyprotic Acids and Bases

Example #1: Polyprotic acids can donate three or more acidic hydrogens and as a result will possess multiple Ka values. 

Example #2: Polyprotic bases can accept 3 or more acidic hydrogens and as a result possess multiple Kb values. 

Concept #1: With even more forms than diprotic species, polyprotic species have even more Ka and Kb values involved. 

Polyprotic Acids and Bases Calculations

Example #3: Calculate the equilibrium concentrations of H3PO4, H2PO4, HPO42-, PO43-, and H3O+ for 0.35 M H3PO4. Ka1 = 7.2 x 10-3, Ka2 = 6.3 x 10-8, and Ka3 = 4.2 x 10-13

Example #4: Determine the pH of 0.250 M sodium hydrogen phosphate, Na2HPO4. Phosphoric acid, H3PO4, contains Ka1 = 7.5 x 10-3, Ka2 = 6.2 x 10-8 and Ka3 = 4.2 x 10-13

Example #5: Determine the pH of 0.150 M citric acid, H3C6H5O7. It possesses Ka1 = 7.4 x 10-4, Ka2 = 1.7 x 10-5 and Ka3 = 4.0 x 10-7