`Cu SO_4 ` on mixing with ` NH_3 (1:4 ratio ) ` does not give test for ` Cu^(2+) ` ions but gives test for ` SO_4^(2-) ` ions why?

Explanation

It is because when `NH_3` coordinates to `Cu^(2+)` ions and it forms the complex `[Cu(NH_3)_4]SO_4` copper ions are present in coordination sphere, therefore they are non-ionisable whereas `SO_(4)^(2-)` ions are counter ions which are ionisable.