[restinpeace]

Correct me if I'm wrong here but I believe that salts that are formed by the synthesis of a weak acid and a weak base are the only salts that can be acidic or basic(the only time you need to check the Ka and Kb).  Ammonium sulphate is made from ammonia(weak base) and sulphuric acid(strong base), correct?  This should mean that it can only be acidic but the sulphate reacts to make it basic because it is the conjugate base of HSO4 not H2SO4.  This would make sense if it were made from hydrogen sulphate but all of the research that I have done has told me that it is not.  Any ideas?

[restinpeace]

also, using an indicator, we decided that pH of ammonium carbonate is about 7 but my calculations say otherwise.  Ka = 5.6E-10
Kb = Kw / 5.6E-11 = 1.8E-4 .  probably just contaminated?

[AWK]

Hydrolysis of ammonium sulphate cannot be calculated using an aproximated formula

[Borek]

HSO₄^- is not as strong as you may think, so SO₄^2- will hydrolize.

And ammonium carbonate should be slightly basic.