Buffers Workbook& Problem Set
Read Chapter 2.5 and complete the workbook as you go. Complete the problem set that follows and show all work for full credit. This Workbook and Problem set is due no later than 3AM the night of September 14th (morning of 9/15/12).
Chapter 2.5:
Define the term Buffer:
What happens to the pH of an un-buffered system when acid is added? When Base is added?
Create your own example of these reactions by adding 1 mL of 0.5M HCl and NaOH to 50 mL of water and calculate the pH.
Write the Henderson-Hasselbalch Equation:
Using HA and A- as the acid and base of a buffer, write the reactions for addition of acid (H+) and base (OH-).
Using a pH of 7.0 and a pKa of 6.8 calculate the pH of adding 1 mL of 0.5M HCl and NaOH to 50 mL of buffer and calculate the pH.
Look at the Table 2.8 what buffer would you use to create a buffer solution with a pH of 8.0 and why?
Buffers have a capacity. What does this mean?
If you want to make an acetic acid buffer solution (pKa = 4.76) of 4.5 what would you do? Could you calculate exactly how much acid/base you would use to make the solution?
In the book “Andromeda Strain” by Michael Chrichton only two people survive a viral attack, a baby with colic and an old man who drinks sterno. How might this be related to buffer systems? (Hint: Think about what Colic and the Sterno would do to the body or more specifically the blood)
Problem Set:
1. Given 0.1 M solutions of acetic acid and sodium acetate, describe the preparation of 1L of 0.1 M acetate buffer at a pH of 5.4.
2. If the internal pH of a muscle cell is 6.8, what is the [HPO42-]/[H2PO4-] ratio in this cell?
3. Given 0.1 M solutions of Na3PO4 and H3PO4, describe the preparation of 1L of a phosphate buffer at a pH of 7.5. What are the molar concentrations of the ions in the final buffer solution, including Na+ and H+?
4. BICINE is a compound containing a tertiary amino group whose relevant pKa is 8.3. Given 1 L of 0.05 M BICINE with its tertiary amino group in the unprotonated form, how much 0.1 N HCl must be added to have a BICINE buffer solution of pH 7.5? What is the molarity of the BICINE in the final buffer?
5. What are the approximate fractional concentrations of the following phosphate species at pH values of 0, 2, 4, 6, 8, 10 and 12?
a. H3PO4
b. H2PO4-
c. HPO42-
d. PO43-
6. Citric acid, a tricarboxylic acid important in intermediary metabolism, can be symbolized as H3A. Its dissociation reactions are:
H3A ó H+ + H2A- pK1 = 3.13
H2A- ó H+ + HA2- pK1 = 4.76
HA2- ó H+ + A3- pK1 = 6.40
If the total concentration of the acid and its anion forms is 0.02 M, what are the individual concentrations of H3A, H2A-, HA2- and A3- at pH 5.2?
7. If 50 mL of 0.01 M HCl is added to 100 mL of 0.05 M phosphate buffer at pH 7.2, what is the resultant pH? What are the concentrations of H2PO4- and HPO42- in this final solution?
8. If 50 mL of 0.01 M NaOH is added to 100 mL of 0.05 M phosphate buffer at pH 7.2, what is the resultant pH? What are the concentrations of H2PO4- and HPO42- in this final solution?
9. If the plasma pH is 7.4 and the plasma concentration of HCO3- is 15 mM, what is the plasma concentration of H2CO3? What is the plasma concentration of CO2(dissolved)? If metabolic activity changes the concentration of CO2(dissolved) to 3 mM, and [HCO3-] remains at 15 mM, what is the pH of the plasma?