Presentation on theme: "Ch 11: Titrations in Diprotic Systems"— Presentation transcript:
1 Ch 11: Titrations in Diprotic Systems Biological Applications - Amino Acids (Sec. 11-1)low pH high pHR = (CH3)2CHCH2 -
2 Finding the pH in Diprotic Systems (Sec. 11-2) 1. The acidic form H2L+The strength of H2L+ as an acid is much, much greater than HL -Ka1 = = 4.7 x 10-3Ka2 = = 1.8 x 10-10So assume the pH depends only on H2L+ and ignore the contribution of H+ from HL.
4 2. The basic form L-Ka1 = = 4.7 x Ka2 = = 1.8 x 10-10Strengths of conjugate bases:for L- Kb1 = Kw/Ka2 = 1.01 x 10-14/1.8 x = 5.61 x 10-5for HL Kb2 = Kw/Ka1 = 1.01 x 10-14/4.7 x 10-3 = 2.1 x 10-12Since the second conj. base HL is so weak, we'll assume all the OH- comes from the L- form.
5 Example: Calculate the pH of a 0.050M solution of sodium leucinate
6 The Intermediate Form The pH of a Zwitterion Solution - Leucine (HL form)