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CEE 680 |
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8 November 2001 |
Closed book, two pages of notes allowed.
Answer all questions. Please state any additional assumptions you made, and show all work.
(50% for both parts) You’re treating a drinking water that contains 120 mg/L of alkalinity. The initial pH is 7.35, and you wish to raise this to 9.10 for purposes of corrosion control.
A. (25%) How much of a caustic soda (NaOH) dose do you need to add to accomplish this if the water goes right into the water main?
B. (25%) Answer the above question, but this time assume you have a large finished water reservoir after caustic addition that allows the water to reach equilibrium with the atmosphere before entering the distribution system.
(50%
for both parts) Zinc forms a series
of complexes with aqueous cyanide.
A. (40%) Sketch out a set of alpha curves
(vs log[ CN- ]) for the Zinc-cyanide system. Assume that the pH is high enough so that
there is no significant formation of HCN.
Use the following stability constants from Stumm and Morgan. Note that these are all overall formation
constants.
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ZnL |
Log b1 = 5.7 |
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ZnL2 |
Log b2 = 11.1 |
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ZnL3 |
Log b3 = 16.1 |
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ZnL4 |
Log b4 = 19.6 |
Using this determine the species composition when the total zinc concentration is 0.1 mM and the total cyanide concentration is 0.5 mM.
B. (10%) How would the answer to this problem change if the pH
was 7.3? Explain qualitatively in words
why this makes a difference, and which way it would shift the equilibria. Be quantitative if you can.
Selected Acidity Constants (Aqueous Solution, 25°C, I = 0)
|
NAME |
FORMULA |
pKa |
|
|
Perchloric acid |
HClO4 = H+ + ClO4- |
-7 STRONG |
|
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Hydrochloric acid |
HCl = H+ + Cl- |
-3 |
|
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Sulfuric acid |
H2SO4= H+ + HSO4- |
-3 (&2) ACIDS |
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Nitric acid |
HNO3 = H+ + NO3- |
-0 |
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Hydronium ion |
H3O+ = H+ + H2O |
0 |
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Trichloroacetic acid |
CCl3COOH = H+ + CCl3COO- |
0.70 |
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Iodic acid |
HIO3 = H+ + IO3- |
0.8 |
|
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Bisulfate ion |
HSO4- = H+ +
SO4-2 |
2 |
|
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Phosphoric acid |
H3PO4 = H+ + H2PO4- |
2.15 (&7.2,12.3) |
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Citric acid |
C3H5O(COOH)3= H+ + C3H5O(COOH)2COO- |
3.14 (&4.77,6.4) |
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Hydrofluoric acid |
HF = H+
+ F- |
3.2 |
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m-Hydroxybenzoic acid |
C6H4(OH)COOH = H+ + C6H4(OH)COO- |
4.06 (&9.92) |
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p-Hydroxybenzoic acid |
C6H4(OH)COOH = H+ + C6H4(OH)COO- |
4.48 (&9.32) |
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Nitrous acid |
HNO2 = H+ + NO2- |
4.5 |
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Acetic acid |
CH3COOH = H+ + CH3COO- |
4.75 |
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Propionic acid |
C2H5COOH = H+ + C2H5COO- |
4.87 |
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Carbonic acid |
H2CO3 = H+ + HCO3- |
6.35 (&10.33) |
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Hydrogen sulfide |
H2S = H+ + HS- |
7.02 (&13.9) |
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Dihydrogen phosphate |
H2PO4- = H+ + HPO4-2 |
7.2 |
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Hypochlorous acid |
HOCl = H+
+ OCl- |
7.5 |
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Boric acid |
B(OH)3 + H2O = H+ + B(OH)4- |
9.2 (&12.7,13.8) |
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Ammonium ion |
NH4+ = H+ + NH3 |
9.24 |
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Hydrocyanic acid |
HCN = H+
+ CN- |
9.3 |
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p-Hydroxybenzoic acid |
C6H4(OH)COO- = H+ + C6H4(O)COO-2 |
9.32 |
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Phenol |
C6H5OH = H+ + C6H5O- |
9.9 |
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m-Hydroxybenzoic acid |
C6H4(OH)COO- = H+ + C6H4(O)COO-2 |
9.92 |
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Bicarbonate ion |
HCO3- = H+ + CO3-2 |
10.33 |
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Monohydrogen phosphate |
HPO4-2 = H+ + PO4-3 |
12.3 |
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Bisulfide ion |
HS- = H+ + S-2 |
13.9 |
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Water |
H2O = H+ + OH- |
14.00 |
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Methane |
CH4 = H+ + CH3- |
34 |
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