Lecture+3+_+4+homework+solutions

Lecture+3+_+4+homework+solutions - Solutions for problems...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Solutions for problems assigned with Lectures 3 and 4 Garrett & Grisham, pg. 45 6. If the internal pH of a muscle cell is 6.8, what is the [HPO 4 2- ]/[H 2 PO 4 - ] ratio in this cell? Answer: The dissociation of phosphoric acid proceeds as follows: + + + + + + 3 4 PO H 2 4 HPO H 4 PO 2 H H 4 PO 3 H the pK a values of 2.15, 7.20 and 12.40 respectively. Now, at pH = 6.8, we expect the first equilibrium to be completely to the right and the last equilibrium to be to the left (i.e., we expect phosphoric acid to be in the doubly or singly protonated forms). From the Henderson Hasselbalch equation we find: pH = pK a + log 10 [A - ] [HA] where [A - ] = [ HPO 4 2 ];[HA ] = [H 2 PO 4 ] log 10 [HPO 4 2 ] [H 2 PO 4 ] = pH pK a [HPO 4 2 ] [H 2 PO 4 ] = 10 (pH pK a ) = 10 (6 .8 7.2) = 0.4 10. Citric acid, a tricarboxylic acid important in intermediary metabolism, can be symbolized as H 3 A. Its dissociation reactions are 6.40 = a pK 3 A H 2 HA 4.76 = a pK 2 HA H A 2 H 3.13 = a pK A 2 H H A 3 H + + + + + + If the total concentration of the acid and its anion forms is 0.02 M, what are the individual concentrations of H 3 A, H 2 A - , HA 2- , and A 3- at pH 5.2? Answer: For citric acid + + + + + + 3 A H 6.40 2 HA H 4.76 A 2 H H 3.13 A 3 H At pH = 5.2 the predominant equilibrium will involve H 2 A and HA 2 -.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
pH = pK a + log 10 [HA 2 ] [H 2 A ] [HA 2 ] [H 2 A ] = 10 (pH pK a ) = 10 (5.2 4.76 ) = 2.754 (1) And, considering the other two equilibria we have [A 3 ] [HA 2 ] = 10 (pH pK a ) = 10 (5.2 6.4 ) = 0.063 (2) and [H 2 A ]
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 6

Lecture+3+_+4+homework+solutions - Solutions for problems...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online