polyprotic acids - University of Texas at Austin Equation used to determine the pH H+ = K a1C a C b Approximate pH 5 Which is what you would expect for a weak acid buffer Case 3 What is the pH of a 0 1 M NaHCO 3 (the most famous antacid)with K a1 = 10-5 and K a2 = 10-11 Where are you on a titration curve? At the first equivalence point Equation used to determine the pH H+ = (K a1 K a2
Chem 321 Lecture 15 - Acid-Base Equilibria Titrations + + M2-K a2 = 5 96 x 10-7 HM-+ H 2O º H2M + OH-K b = Kw Ka1 = 8 33 x 10-13 We expect the solution to be acidic because Ka2 >> Kb If we ignore the base hydrolysis reaction and treat HM-solely as a weak acid, [H 3O +] equil = 1 7 x 10-4 M and pH • 3 76 However, it turns out that the base hydrolysis reaction proceeds to nearly the
Chapter 9: POLYPROTIC ACID-BASE EQUILIBRIA K a1 = K 1 2 H 2A-is treated as the intermediate form of a diprotic acid 3 HA 2-is also treated as the intermediate form of a diprotic acid However, HA 2-is “surrounded” by H 2A-and A 3-, so the equil constants to use are K a2 (= K 2) and K a3 (= K 3) 4 A 3-is treated as monobasic K b1 = Kw K a3 22
15 Titration Curves for Complex Acid Base Systems 92 15 Titration Curves for Complex Acid Base Systems (1) Two acids or two bases of different strength (2) An acid or a base that has two or more acids or bases of different strengths
POLYPROTIC ACIDS AND BASES: Very important! 18-9 NOTE: (i) pK b = -log K b (ii) just like pK a, strength of base increases with decreasing pK b (See Table 18 6) The bigger is K b, the more OH-is generated The smaller is pK b, the more OH-is generated
Microsoft Word - Determination of Ka of Weak Acids Lab Phosphoric acid is a triprotic acid (three ionizable hydrogens) The values of its stepwise ionization constants are Ka1 =7 5 x 10-3, K a2 =6 2 x 10-8, K a3 =4 2 x 10-13 1 Write the chemical equation for the first ionization reaction of phosphoric acid with water 2 Write equilibrium constant expression constant expression (K a1) for this