ENCE 433 Dr.
Alba Torrents
ENVIRONMENTAL ENGINEERING ANALYSIS Spring 2001
Homework Set #
5
SOLUTIONS
1.
Let CA
= molarity of the acid solution
Then
No. mmol acid = 25.00 mL CA
mmol/mL
At
the equivalent point:
No. mmol base added = No. mmol acid
originally present
No. mmol OH- added = (32.80 mL)(0.1500M) = (25.00mL) (CA)
2.
The pH of this buffer is given by:
Originally both NH+4 and NH3
are 0.200 M. The dilution with water
decreases both these concentrations to 0.100 M, but the ratio 
remains 1:1.
Thus the pH remains constant on dilution.
3.
PBE
[H2S] + [H+] = [OH-] + [S-2] + [C2H5COO-]
AS the main concentration is bisufide that can act either an acid or a base, the pH will be colse to 7 and thus [H+] and [OH-] relatively small. We can look at all the possible intersection point and choose the one that involves the higher concentrations
which reduces to: [H2S] = [C2H5COO-]
Solution
Composition
|
Species |
Graph C |
pC |
|
H+ |
3e-9 |
8.5 |
|
OH- |
3e-6 |
5.5 |
|
H2S |
3e-4 |
3.5 |
|
Na+ |
1e-2 |
2.0 |
|
HS- |
1e-2 |
2.0 |
|
S-2 |
4e-8 |
7.4 |
|
HPr |
6e-8 |
7.2 |
|
Pr- |
3e-4 |
3.5 |
ENE
[Na+] + [H+] = [OH-] + [HS-] + 2[S-2] + [C2H5COO-] + [Cl-]
which reduces to: [Na+] - [Cl-] = [HS-] = 0.005
pH = 7.02