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Problems1solution - Homework Assignment 01(answers 1(a...

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page 1 1. (a) HPO 4 2– If the pKa’s of a polyprotic acid differ by ~ 3 pH units or more, then each ionization can be analyzed independently by the Henderson-Hasselbalch equation. To answer this question you do not necessarily need to perform a calculation; you just need to know the pKa’s can be treated independently and the relationship between degree of ionization that occurs at pH values surrounding the pKa as shown in the diagram below. pH 10 is about midway between pKa 2 and pKa 3 , about 2.8 pH units higher than pKa 2 and 2.4 lower than pKa 3 . Thus, pKa 1 is not relevant to this problem. As indicated in the diagram below, we know that at greater than 2 pH units above pKa 2 the conjugate acid, H 2 PO 4 , is fully ionized to HPO 4 2– , and at greater than 2 pH units below pKa 3 little or no ionization (deprotonation) of HPO 4 2– as occurred. Thus, HPO 4 2– is the dominate species present at pH 10. 1. (b) pH = 2.15
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This note was uploaded on 04/11/2011 for the course BCHM 561 taught by Professor Mr. during the Spring '10 term at Purdue.

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Problems1solution - Homework Assignment 01(answers 1(a...

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