[Twickel]

Hi
With regards to metal ion hydrolysis and there concentrations over pH, I do not understand some concepts.

Slide 4 has a diagram and it says " but the gibbsite does not all disolve until the sum of all dissolved species equal 10*-4 M near pH=4), but the same diagrams shows AlOH4- dominant at above ph=8, how can this be, if the gibbsite doesnt dissolve until ph=4, and at phs lower then 4 the other species are present?

Also how can the total concentration "exceed" the original concentration?


Thanks.

[AWK]

http://en.wikipedia.org/wiki/Amphoteric

[Twickel]

ALOH3   ALOH4 - + H+ , so what is going on in this reaction? Is AlOH3 acting as an acid in alkaline solution?

My notes have all the hydrolysis reactions of Al3+, later on they say AlOH3 is independent of pH as it is fixed by solid gibbsite, yet there are two clear equations which involve AlOH3 and Hydrogen ions
ALOH3   ALOH4 - + H+

and AlOH₂⁺  AlOH₃ + H⁺

[Twickel]

Ignore the first sentence of the last post, ( could not modify it).