Question

eurse Home <Post-class assignment - Week 9 Problem 21.49 - Enhanced - with Feedback Serine has pK, values of 2.21 and 9.15. At what pH will serine exist in the indicated form? - Part A H₂N. LÓ HEN HO 50% HO 50% Express your answer using two decimal places. V AEO O ? pH = 5.68 Submit Previous Answers Request Answer o RH

Answer 1

Part A

Correct answer: pH = 9.15

Each of the two structures will be 50 % at the 2nd half equivalence point of the titration of serine. At second half equivalence point pH = pK_a of -NH₃⁺ = 9.15.

Part B

Correct answer: pH = pI = (2.21 + 9.15)/2 = 5.68

At isoelectric point (pI) the net charge on the molecule = 0. This is only possible when the molecule exist totally or 100 % as the zwitterionic form given in part B.

Part C

Correct answer: pH = 2.21

Each of the two structures will be 50 % at the 1st half equivalence point of the titration of serine. At first half equivalence point pH = pK_a of -COOH = 2.21.