PRINCIPLES OF WATER CHEMISTRY
METALS IN AQUEOUS SYSTEMS
PLEASE NOTE THE UNUSUAL DUE DATE FOR THIS HOMEWORK
DUE ON MONDAY 11/30/2020, at 5:00 PM
- Should be typed since using MINTEQ
- If typing, using “Word”, select “INSERT” and “ EQUATION” and then “ INSERT NEW EQUATION” to type in chemical and mathematical formulas.
- SUBMISSION should be THROUGH CANVAS ONLY. Email submissions are not be accepted
Question (100 points) – Using MINTEQ and following the solution strategy given in Lecture-35, solve the following problem by describing in details the different steps used to address the 4 points below.
A water with a pH of 8.1 contains 2.0 meq/L of alkalinity, 0.2 mmol/L of TOTPO4, and a negligible concentration of Ca2+. In this water, the alkalinity (ALK) is all from PO4 and CO3 species. If lime (Ca(OH)2) is added to this aqueous solution with the goal of removing 95% of TOTPO4 by precipitation of Ca5OH(PO4)3(s):
- Draw a log C – pH diagram showing Ca2+ activity in equilibrium with each of two solids: CaCO3(s) and Ca5OH(PO4)3(s), for the initial TOTCO3 and TOTPO4. Which solid will precipitate first?
- Plot pH vs. lime dose, if no solid precipitates. Consider additions of 0 to 5×10-4M lime. Add a curve to the plot from part (a) showing log(Ca2+) vs. pH during the titration.
- Repeat part (b), allowing for precipitation of solids. How much lime must be added, and what will the pH be, when the TOTPO4 target is reached?
- If more lime is added, can the second solid precipitate? If so, under what conditions? If no, why not?