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CEE 680 |
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20 November 2008 |
Closed book, two pages of notes allowed.
Answer all questions. Please state any additional assumptions you made, and show all work.
(55% for both parts) 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 |
25 |
6.50 |
|
#2 |
10 |
300 |
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?
C. How many mg/L of caustic soda (NaOH) must be added to the unequilibrated blended water in part “A” to raise the pH to 9.80 ?
(45%
for both parts) Aqueous fluoride
forms strong complexes with many metals.
The following two part problem concerns complexes with Beryllium.
A.
(20%)
Attached is an accurate graph of alpha values (vs log[ F-]) for the Beryllium-Fluoride
system (equilibria data shown below). Using
this graph determine the complete species composition when the total Beryllium
concentration is 0.10 mM and the total fluoride concentration is 0.40 mM. Ignore the possible formation of any other
complexes other than those from Be and F; also ignore any possible
precipitation reactions. Assume the
water is a neutral pH.
B.
(20%)
Describe in qualitative terms the impacts of pH on this system.
Estimate in quantitative terms what the concentrations of each of the
species would be if the pH were 2.2, instead of 7.0, and explain how you got
these.
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) |
|
|
Citric acid |
C3H5O(COOH)3= H+ + C3H5O(COOH)2COO- |
3.14 (&4.77,6.4) |
|
|
Hydrofluoric acid |
HF = H+ + F- |
3.2 |
|
|
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 |
|
|
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+ + |
14.00 |
|
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Methane |
CH4 = H+ + CH3- |
34 |
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