|
CEE 680 |
|
16 November 2000 |
Closed book, two pages of notes allowed.
Answer all questions. Please state any additional assumptions you made, and show all work.
(50%) Two raw drinking waters are mixed as they enter the
headworks of a water treatment plant.
The two are characterized as follows:
|
Water |
Flow (MGD) |
Alkalinity (mg/L as CaCO3) |
pH |
|
#1 |
20 |
70 |
6.98 |
|
#2 |
10 |
220 |
8.85 |
A. What will the pH of the blended water be immediately after mixing?
B. What will the pH of the blended water be after it has reached equilibrium with the bulk atmosphere?
1. (50%) You are trying to control algal growths in a
lake containing water that is well buffered at neutrality (pH 7.00). Accordingly, you have just added 10 µM of Cu+2
for this purpose. However, you
discover that the intended effect did not occur. Careful analysis of this lake water showed a substantial presence
of EDTA. The total EDTA concentration
(YT, the sum of all species) was measured as 20 µM.
A. How much free copper
actually existed? Assume the system is
at equilibrium, and ignore any copper hydrolysis species.
B. How much manganese (+II)
would have to be introduced into this water to reduce the degree of copper
binding by EDTA to 50% of its total concentration (i.e., CuEDTA = 0.5*CuT)?
C. Describe in qualitiative
terms how your approach to solving this problem would differ if the ligand was
not EDTA but some monodentate ligand such as ammonia. Lets presume that you do not have access to MINEQL or any similar
computer code.
Important Equilibria
|
|
Equilibrium |
Log K |
|
|
Y-4 + H+ = HY-3 |
10.26 |
|
|
Y-4 + 2H+ = H2Y-2 |
16.42 |
|
|
Y-4 + 3H+ = H3Y- |
19.09 |
|
|
Y-4 + 4H+ = H4Y |
21.09 |
|
|
Y-4 + 5H+ = H5Y+ |
22.59 |
|
|
Y-4 + 6H+ = H6Y+2 |
22.59 |
|
|
Y-4 + Cu+2 = CuY-2 |
18.80 |
|
|
Y-4 + Mn+2 = MnY-2 |
13.87 |
Selected
Acidity Constants (Aqueous Solution,
25°C, I = 0)
|
NAME |
FORMULA |
pKa |
|
|
Perchloric acid |
HClO4 = H+ + ClO4- |
-7 STRONG |
|
|
Hydrochloric acid |
HCl = H+ + Cl- |
-3 |
|
|
Sulfuric acid |
H2SO4= H+ + HSO4- |
-3 (&2) ACIDS |
|
|
Nitric acid |
HNO3 = H+ + NO3- |
-0 |
|
|
Hydronium ion |
H3O+ = H+ + H2O |
0 |
|
|
Trichloroacetic acid |
CCl3COOH = H+ + CCl3COO- |
0.70 |
|
|
Iodic acid |
HIO3 = H+ + IO3- |
0.8 |
|
|
Bisulfate ion |
HSO4- = H+ +
SO4-2 |
2 |
|
|
Phosphoric acid |
H3PO4 = H+ + H2PO4- |
2.15 (&7.2,12.3) |
|
|
o-Phthalic acid |
C6H4(COOH)2 = H+ + C6H4(COOH)COO- |
2.89 (&5.51) |
|
|
Citric acid |
C3H5O(COOH)3= H+ + C3H5O(COOH)2COO- |
3.14 (&4.77,6.4) |
|
|
Hydrofluoric acid |
HF = H+
+ F- |
3.2 |
|
|
Aspartic acid |
C2H6N(COOH)2= H+ + C2H6N(COOH)COO- |
3.86 (&9.82) |
|
|
m-Hydroxybenzoic acid |
C6H4(OH)COOH = H+ + C6H4(OH)COO- |
4.06 (&9.92) |
|
|
p-Hydroxybenzoic acid |
C6H4(OH)COOH = H+ + C6H4(OH)COO- |
4.48 (&9.32) |
|
|
Nitrous acid |
HNO2 = H+ + NO2- |
4.5 |
|
|
Acetic acid |
CH3COOH = H+ + CH3COO- |
4.75 |
|
|
Propionic acid |
C2H5COOH = H+ + C2H5COO- |
4.87 |
|
|
Carbonic acid |
H2CO3 = H+ + HCO3- |
6.35 (&10.33) |
|
|
Hydrogen sulfide |
H2S = H+ + HS- |
7.02 (&13.9) |
|
|
Dihydrogen phosphate |
H2PO4- = H+ + HPO4-2 |
7.2 |
|
|
Hypochlorous acid |
HOCl = H+
+ OCl- |
7.5 |
|
|
Boric acid |
B(OH)3 + H2O = H+ + B(OH)4- |
9.2 (&12.7,13.8) |
|
|
Ammonium ion |
NH4+ = H+ + NH3 |
9.24 |
|
|
Hydrocyanic acid |
HCN = H+
+ CN- |
9.3 |
|
|
p-Hydroxybenzoic acid |
C6H4(OH)COO- = H+ + C6H4(O)COO-2 |
9.32 |
|
|
Phenol |
C6H5OH = H+ + C6H5O- |
9.9 |
|
|
m-Hydroxybenzoic acid |
C6H4(OH)COO- = H+ + C6H4(O)COO-2 |
9.92 |
|
|
Bicarbonate ion |
HCO3- = H+ + CO3-2 |
10.33 |
|
|
Monohydrogen phosphate |
HPO4-2 = H+ + PO4-3 |
12.3 |
|
|
Bisulfide ion |
HS- = H+ + S-2 |
13.9 |
|
|
Water |
H2O = H+ + OH- |
14.00 |
|
|
Ammonia |
NH3 = H+ + NH2- |
23 |
|
|
Methane |
CH4 = H+ + CH3- |
34 |
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