Question

Sodium hydrogen sulphate is not an acid but it dissolves in water to give hydrogen ions.Why?

Answer 1

Sodium hydrogen sulphate dissolves in water but does not produce a hydrogen ion. The reason there is a hydrogen ion is that NaHCO4 (Sodium hydrogen sulphate) still has the acidic hydrogens left from the carbonic acid. This is why sodium hydrogen sulphate can donate a hydrogen ion when reacted with a strong base. For example, if sodium hydrogen sulphate reacts with sodium hydroxide, it produces sodium sulphate and water (which has got the hydrogen ion). 

Answer 2

Sodium Hydrogen Sulphate - Fromula- NaHSO4
It is formed by reaction of Sodium Hydroxide and Sulphuricacid

[Neutralization reaction]:

NaOH  + H2SO4-----> NaHSO4 +H2O

Sodium Hydrogen Suplhate contains One of the Hydrogen Ion given by sulphuric acid , so it can donate H+ion to a strong base even though it is not as acid
The reaction is as followed;
NaHSO4 +NaOH-----> Na2SO4 + H2O

Conclusion :
Sodium Hydrogen Sulphate is not an acid but it dissolves in water to give hydrogen ions.