CEE 680

 

Fall 2011

Water Chemistry

 

Homework  #8

 

 

1. Prepare a complete Log C vs pH diagram for a system containing pure water and an excess of a-aluminum hydroxide, also known as Gibbsite (25ºC and I=0).  Use the equilibrium constants in Stumm & Morgan’s Table A6.1 (after page 324 in the 3rd edition) or the values in the tables on pgs 241 and 242 in the 2nd edition (see table below).  Show how you determined the equations for each of the lines.

 

 

2. Determine the pH of this solution.

 

 

3. Determine the pH of a 0.1 mM solution of alum (aluminum sulfate).

 

 

 

Equilibrium Data

Species

Equilibrium

Log K

Benjamin[1]

Stumm & Morgan[2]

Al(OH)3

Al(OH)3 = Al+3 + 3OH-

-33.23

-33.5

AlOH+

Al+3 + OH- = Al(OH)+2

9.01

9.0

Al(OH)2+

Al+3 + 2OH- = Al(OH)2+

17.90

18.7

Al(OH)3o

Al+3 + 3OH- = Al(OH)3o

26.00

27.0

Al(OH)4-

Al+3 + 4OH- = Al(OH)4-

33.00

33.0

Al3(OH)4+5

3Al+3 + 4OH- = Al3(OH)4+5

 

42.1

Al13O4(OH)24+7

13Al+3 + 32OH- = Al13O4(OH)24+7 + 4H2O

 

349.3

 

 

Assigned: 18 Nov 11

Due: 28 Nov 11

 


[1] Table 8.7 for Kso, Table 8.2 for hydroxide complexes

[2] Table A6.1 in 3rd edition, following page 324