Question

Draw a pC-pH solubility diagram for gibbsite, Al(OH)3 (s)

Al(OH)3 (s) ⇌ Al3+ + 3OH-

LogKs0 = -34.0

Al3+ + H2O ⇌ AlOH2+ + H+

LogKs1 = -5.0

AlOH2+ + H2O ⇌ Al(OH)2 - +2H+

LogKs2 = -10.1

Al(OH)3 0 + H2O ⇌ Al(OH)3 0 +3H+

LogKs3 = -16.9

Al3+ + 4H2O ⇌ Al(OH)4 - + 4H+

LogKs4 = -22.7

Graph the pH on the x-axis and the concentration of the aluminum species on the y-axis. Assume gibbsite dissolves in pure water and that no gasses are present. Use activity coefficients of 1.0. Show all work including and derivations of speciation lines.

a. Mark your graph with the stability field of gibbsite (indicate this region on graph).

b. Is any aqueous alumina in present present within the gibbsite stability field of this system?

Answer 1

(a). Below the line compounds are soluble and above the line it is insoluble.(b) yes