I know that theory, but I don't understand why those compounds make an acidic solution.
KAl(SO4)2-->?
NaHSO4 made from a strong base (NaOH) and a strong acid (HSO4-) so it has to make a neutral solution.
NaH2PO4 same as above only that the H2PO4- acid is less strong than HSO4- so it should make a basic solution, but they are all acidic.