CEE 680 |
16 November 1999 |
SECOND EXAM
Closed book, two pages of notes allowed.
Answer all questions. Please state any additional assumptions you made, and show all work.
Problem #1: (40%) Carbonate System.
Two raw drinking waters are mixed in equal proportions as they enter the headworks of a water treatment plant. The two are characterized as follows:
Water |
Alkalinity (mg/L as CaCO3) |
pH |
A |
70 |
7.31 |
B |
220 |
9.12 |
What will the pH of the blended water be?
Problem #2: (60%) Precipitation/Dissolution
Aluminum Solubility
Equilibria |
Log K |
AlOH3(s) (amorphous) + 3H+ = Al+3 + 3 H2O |
10.8 |
Al+3 + H2O = AlOH+2 + H+ |
-4.97 |
Al+3 + 2H2O = Al(OH)2+ + 2H+ |
-9.3 |
Al+3 + 3H2O = Al(OH)3(aq) + 3H+ |
-15.0 |
Al+3 + 4H2O = Al(OH)4- + 4H+ |
-23.0 |
AlPO4•2H2O(s) (variscite) = Al+3 + PO4-3 + 2H2O |
-21 |
H3PO4 = H+ + H2PO4- |
-2.15 |
H2PO4- = H+ + HPO4-2 |
-7.2 |
HPO4-2 = H+ + PO4-3 |
-12.3 |