Ch.15 - Acid and Base EquilibriumWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Sections
Identifying Acids and Bases
Arrhenius Acid and Base
Bronsted Lowry Acid and Base
Amphoteric
Lewis Acid and Base
pH and pOH
Ka and Kb
Ionic Salts
Diprotic Acid
Polyprotic Acid
Additional Practice
Strong Acid-Base Calculations
Weak Acids
Additional Guides
Strong Acids and Strong Bases (IGNORE)
Conjugate Acids and Bases
Weak Bases
LearnAdditional Practice

A polyprotic acid possesses more than 2 hydronium ions (H+). 

Polyprotic Acids

Our understanding of diprotic acids and bases can be used to understand polyprotic acids and bases. 

Concept #1: The most common type of polyprotic acid is the triprotic acid, which contains 3 acidic hydronium ions. 

Concept #2: Triprotic bases contain 3 Kb values, so they would have 3 equilibrium equations. 

Concept #3: As a result of these equations for polyprotic acids and bases the relationship between Ka and Kb can be established. 

Example #1: Determine the pH of 0.300 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 #2: Determine the pH of 0.300 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. 

Previous SectionDiprotic Acid
Additional Problems
In a triprotic acid which Ka value is largest in value? a) Ka1 b) Ka2 c) Ka3 d) They are all equal. 
In a triprotic acid, which Ka has the highest value? A) Ka1 B) Ka2 C) Ka3 D) Kb1 E) Kb2
Determine the pH of a 0.03 M solution of NaH 2PO4? Assume H3PO4 has a pKa1 of 2.1 and a pKa2 of 7.2 and a pKa3 of 12.7.  1. 4.36 2. 7.11 3. 4.65 4. 7.40 5. 9.95 6. 1.81
Consider a solution that is 0.10 M in a weak triprotic acid which is represented by the general formula H3A with ionization constants K1 = 1.0 × 10−3 , K2 = 1.0 × 10−8 , and K3 = 1.0 × 10−12. What is the pH of the solution? 1. 2.15 2. 2.25  3. 2.02 4. 2.35 5. 2.54
Identify the triprotic acid. A) HNO3 B) H3PO4 C) H2CO3 D) HFO4 E) H2SO4
Which below correctly describes the relationship amongst the successive p Ka and Kb values for most polyprotic acids? a) pKa1 > pKa2 > pKa3b) pKa3 > pKa2 > pKa1c) Kb1 > Kb2 > Kb3d) Ka1 < Kb1e) cannot be predicted
Phosphoric acid (H3PO4) is characterized by three reactions for stepwise dissociation. Arrange the following species in the order of decreasing concentration in an aqueous solution of H3PO4. Clearly indicate the order of concentration change. JUSTIFY your answer.H3PO4          H 2PO4-          HPO 42-          PO 43-          H 3O+  
For the polyprotic acid H3PO4 (phosphoric acid), which of the following expressions would correspond to Ka3?1. H3PO4 ⇌ PO43− + 3 H+2. PO43− + 3 H+ ⇌ H3PO43. HPO42− ⇌ PO43− + H+4. H2PO4− ⇌ HPO42− + H+5. H3PO4 ⇌ H2PO4− + H+ 
Identify the weak triprotic acid.A) CH3COOHB) H3PO3C) H3PO4D) H2SO4E) H2SO3
What is the pH of a solution of 0.25 M K3PO4, potassium phosphate? GivenKa1 = 7.5 * 10-3Ka2 = 6.2 * 10-8Ka3 = 4.2 * 10-13
Phosphoric acid is a triprotic acid (Ka1 = 6.9 x 10-3, Ka2 = 6.2x 10-8, and Ka3 = 4.8 x10-13). To find the pH of a buffer composed of H2PO4- (aq) and HPO42- (aq), which pKa value would you use in the Henderson-Hasselbalch equation?Calculate the pH of a buffer solution obtained by dissolving 13.0 g of KH2PO4(s) and 26.0 g of Na2HPO4(s) in water and then diluting to 1.00 L.
Farmers who raise cotton once used arsenic acid, H3AsO4 , as a defoliant at harvest time. Arsenic acid is a polyprotic acid with K1 = 2.5 x 10-4 , K 2 = 5.6 x 10-8 , and K3 = 3 x 10-13 . What is the pH of a 0.500 M solution of arsenic acid?A) 0.85B) 1.95C) 3.90D) 4.51