Question on 6D.11 and writing chemical equations

[Maham Kazmi 2J]

For parts e and f, I understand why it would be acidic in both situations. However, the solutions guide was a bit confusing to me as to why we would write the acid as Al(H2O)6 ^ 3+ rather than just Al3+?

[alexjung1A]

That is because it forms a (octahedral) complex in water. Think of the coordination compounds we've been studying, it's pretty much the same thing. I believe this happens to all the other highly charged metal cations in water as well.