Problem 1
I. Acetic acid has a Ka of 1.8 x 10-5 M.
What is the pH of 50 ml of a 0.1 M solution?
Answer - 2.87
II. At pH 5.2 what fraction of total acetate is in the base
form?
Answer - 0.74
III. Glycine has pKs of 2.35 and 9.78. What is the percentage of
each form at pH 8.4?
Answer - 8.9 x 10-5%, 95.997%, 4%
IV. You start with 50 ml of 0.1 Molar glycine.
How much 1 M HCl needs to be added to obtain a pH of 3.1?
Answer - 0.755 ml
V. The Ka of NH+4 is 5.55 x 10-10
M. What is the pH of a 0.5 M NH4OAc solution?
Answer - 7.0
VI. Given a
peptide with the sequence Gly-Asp-His-His-Phe-Tyr-His-Glu-Leu-Arg-Trp.
|
Group |
pK1 |
pK2 |
pK3 |
|
a-amino |
8.2 |
||
|
Phe |
2.16 |
9.18 |
|
|
Tyr |
2.20 |
9.11 |
10.13 |
|
His |
1.80 |
9.33 |
6.04 |
|
Glu |
2.10 |
9.47 |
4.07 |
|
Leu |
2.33 |
9.74 |
|
|
Arg |
1.82 |
8.99 |
12.48 |
|
Trp |
2.43 |
9.44 |
|
|
Gly |
2.35 |
9.78 |
|
|
Asp |
1.99 |
9.90 |
3.90 |
|
a-carboxyl |
3.5 |
Calculate the charge (to the nearest 0.1 of a pH unit) at pH
4, 7 and 11. Calculate the pI to the nearest 0.05 pH unit.
Answer - +3.20, -0.76, -2.91, 6.34
VII. What is the pH of the following concentrations of HCl; NaOH
|
|
Answers |
|
|
10-3 M |
3 |
11 |
|
10-5 M |
5 |
9 |
|
10-7 M |
6.79 |
7.21 |
|
10-8 M |
6.98 |
7.02 |
VIII.
The three pKs of Arg are 1.82, 8.99 and 12.48.
Write an expression for the relative fraction of the form of
Arg that has no net charge.
Answer 