Henderson-Hasselbalch Practice
Problems for BB 450
Useful pKas - Acetic acid = 4.76. For the phosphate buffers below, you
can use pKa1 = 2.1, pKa2 = 6.83, and pKa3 = 10.1
1. Using the Henderson-Hasselbalch equation, explain why when a
solution is at a pH below the pKa for an acid that more than 50% of the
molecules have the proton on (not off).
2. Using the Henderson-Hasselbalch equation, determine the ratio of
acetate ion (salt) to acetic acid (acid) present in a 1 M solution at the
following pHs
a. pH = 1
b. pH = 2
c. pH = 3
d. pH = 5
e. pH = 7
f. pH = 9
3. At physiological pH (7.0), what will be the predominant form of
phosphate present in cells? (H3PO4? H2PO4-? HPO4-2, or PO4-3?) Justify your
answer using the Henderson-Hasselbalch equation.
4. Formic acid has a pKa of 3.75 and acetic acid has a pKa of 4.76. Why
do we consider formic acid to be a "stronger" acid than acetic acid? Your
answer should have a mathematical basis.
5. A new molecule is discovered, called bleemium. It contains ionizable
groups with the following pKas:
Carboxyl #1 pKa = 2.2
Carboxyl #2 pKa = 4.4
Amine #1 pKa = 5.0
Amine #2 pKa = 8.5
Amine #3 pKa = 9.5
Predict the charge on bleemium at the following pHs:
1.0
7.0
11.0
6. One liter of 1M acetate buffer at pH = 4.5 is mixed with 600 ml of .5M
acetate buffer at pH = 4.8 and then one liter of HCl (0.1M) is added. What is
the pH of the final solution?