Naming Compounds: How to Write (NH4)+ Al3+ SO4 2-

[minimario]

How do you name compounds such as Ammonium Aluminium Sulfate?

It should first be (NH4)+ then Al 3+ and SO4 2-, but how do you put then together? How do you know it is [latex]NH_4 AL (SO_4)_2[/latex] instead of, say, [latex] (NH_4)_3 Al (SO_4)_3 [/latex]?

Thanks!

 

[Borek]

I am afraid it is one of the things you have to remember. That is, you don't have to remember every possible salt separately, most mixed salts containing ammonium and Me³⁺ have NH₄Me(SO₄)₂ formula. But when it comes to hydration waters there are no rules (or more precisely, the rule is "whatever crystal form has the lowest energy" - but calculating crystal energy is so difficult, it is easier to prepare the salt and determine amount of water experimentally).