[Winga]

For this two complexes:
[Al(OH2)6]^3+   &   [Fe(OH2)6]^3+

The Al^3+ one is moe acidic. Why?

I have found 2 answers:

1. The charge to size ratio of Al^3+ is higher so the charge-charge repulsion of this metal center and the acidic proton is also higher.

2. The Al^3+ has a higher polarizing power that it polarizes the O-H bond.

Which one is more suitable for explaining this case?

Is there any better explanation?

[Demotivator]

Who cares, though I prefer the second.

[Tetrahedrite]

The difference in acidity is almost certainly due to the relative stabilities of other metal-hydroxy complelexes ie Al(OH)2 + is probably more stable than Fe(OH)2 + resulting in more protons being formed in the Al solutions