ENVIRONMENTAL ENGINEERING ANALYSIS Fall 1996
Homework Set #6 Out: October 31 Due: November 5
SOLUBILITY
1. A wastewater contains 5 mg/L total Cd(II). If we only consider the first hydrolysis (formation of CdOH+),
a. Calculate the pH at which Cd(OH)2 (s) precipitation begins.
b. Calculate the pH at wich [Cd+2] in equilibrium with the solid phase
is 30 g/L.
c. What is the total soluble Cd(II) at the pH = 10?
2. For each of the following equilibrium systems indicate whether
the effect of a small addition is an increase, decrease or
no effect on the property.
| System | Addition | Effect on | |
| H2O (s) | ZnO | pH | |
| AgCl(s)/H2O | NaCl | [Ag+] | |
| Ni(OH)2(s)/H2O | NaOH | [Ni+2] | |
| PbSO4(s)/H2O | H2O | solubility |
3.
a. Compute the solubility of Fe(OH)2(s) when you add it to pure
water (pKso = 14.5).
b. What would be the final pH?
b. How would [Fe+2] change if the pH is decreased? Why?
d. Compute [Fe+2] at pH = 5