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CEE 680 |
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16 December 2000 |
FINAL EXAM
Closed book, three pages of notes allowed.
Answer all questions. Please state any additional assumptions you made, and show all work. If you don’t have time to complete a section, please describe how you would solve the problem (without using MINEQL).
Magnesite (MgCO3 (s)) and Brucite (Mg(OH)2 (s)) are two important magnesium-bearing minerals.
1. Prepare a solubility diagram (log C vs pH) for a water in equilibrium with magnesium hydroxide and magnesium carbonate. Assume the water has 10-2.5 M total carbonates. Show the MgT line and indicate where precipitation will occur and the type of precipitate.
2. Prepare a predominance diagram, showing the precipitates and major soluble species (in areas where there are no precipitates). As would be typical for a problem of this type, make pH the x-axis, and log total carbonate (CT), the y-axis. Assume a total soluble magnesium concentration of 1 mM..
Ozone (O3) is one of the most powerful chemical oxidants used for the purification of waters and wastewaters. Its final reduced form is usually oxygen and water. Ozone is also a naturally-occurring oxidant that is produced in sunlit surface waters, in urban smog and in the upper atmosphere. The following questions concern the possible oxidation of aluminum by ozone.
1. Write a balanced equation for the oxidation of aluminum metal to Al ion by ozone
2. Determine the stoichiometry of this reaction (e.g., mg-O3/mg-Al).
3. Determine the log K for this reaction
4. Calculate the equilibrium ratio of trivalent Al ion to zero-valent Al solid at pH 7, and in the presence of 10-5 atm ozone.
5. Discuss the implications of these calculations
Some important equilibrium constants:
|
Equilibria |
Log K |
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Mg(OH)2 (s) = Mg+2 + 2OH- |
-11.6 |
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Fe+3 + H2O = FeOH+2 + H+ |
-2.19 |
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Mg+2 + H2O = MgOH+ + H+ |
-11.44 |
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MgCO3 (s) = Mg+2 + CO3-2 |
-7.5 |
Some
important half-cell reactions
|
Equ# |
Half
Cell Reaction |
DEo (Volts) |
|
1 |
O2(g) + 4H+ + 4e- = 2H2O |
+1.23 |
|
2 |
Mn+3 + e- = Mn+2 |
+1.51 |
|
3 |
Mn+4 +
e- = Mn+3 |
+1.65 |
|
4 |
MnO4- + 8H+ + 5e- = Mn+2 + 4H2O |
+1.49 |
|
5 |
Fe+3 +
e- = Fe+2 |
+0.77 |
|
6 |
Cu+2 + e- = Cu+ |
+0.16 |
|
7 |
O3 (g) + 2H+ + 2 e- = O2 (g) + H2O |
+2.07 |
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8 |
Al+3 + 3e- = Al(s) |
-1.68 |
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9 |
S(s) + 2H+ + 2e- = H2S (g) |
+0.17 |
Properties of Selected Elements
|
Element |
Symbol |
Atomic # |
Atomic Wt. |
Valence |
Electronegativity |
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Aluminum |
Al |
13 |
26.98 |
3 |
1.47 |
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Calcium |
Ca |
20 |
40.08 |
2 |
1.04 |
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Carbon |
C |
6 |
12.01 |
2,4 |
2.50 |
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Copper |
Cu |
29 |
63.54 |
1,2 |
1.75 |
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Hydrogen |
H |
1 |
1.01 |
1 |
2.20 |
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Magnesium |
Mg |
12 |
24.31 |
2 |
1.23 |
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Manganese |
Mn |
25 |
54.94 |
2,3,4,6,7 |
1.60 |
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Oxygen |
O |
8 |
16.00 |
2 |
3.50 |
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Potassium |
K |
19 |
39.10 |
1 |
0.91 |
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Sodium |
Na |
11 |
22.99 |
1 |
1.01 |
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Strontium |
Sr |
38 |
87.62 |
2 |
0.99 |
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Sulfur |
S |
16 |
32.06 |
2,4,6 |
2.44 |
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Selected Acidity Constants
(Aqueous Solution, 25°C, I = 0)
|
NAME |
FORMULA |
pKa |
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Perchloric acid |
HClO4 = H+ + ClO4- |
-7 |
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Hydrochloric acid |
HCl = H+ + Cl- |
-3 |
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Sulfuric acid |
H2SO4= H+ + HSO4- |
-3 |
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Nitric acid |
HNO3 = H+ + NO3- |
-0 |
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Bisulfate ion |
HSO4- = H+ +
SO4-2 |
2 |
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Phosphoric acid |
H3PO4 = H+ + H2PO4- |
2.15 |
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o-Phthalic acid |
C6H4(COOH)2 = H+ + C6H4(COOH)COO- |
2.89 |
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p-Hydroxybenzoic acid |
C6H4(OH)COOH = H+ + C6H4(OH)COO- |
4.48 |
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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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Aluminum ion |
Al(H2O)6+3 = H+ + Al(OH)(H2O)5+2 |
4.8 |
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Carbonic acid |
H2CO3 = H+ + HCO3- |
6.35 |
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Hydrogen sulfide |
H2S = H+ + HS- |
7.02 |
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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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Ammonium ion |
NH4+ = H+ + NH3 |
9.24 |
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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 |