當NaOH同H2SO4react ge時候，出黎ge點解會係NaHSO4而唔係Na2SO4?

其實當一種acid 唔係monobasic acid (eg. HCl,HNO3,CH3COOH) 而係 dibasic (eg H2SO4, H2CO3) or tribasic (H3PO4)or HnX where n > 1 o既時候，有機會出2 type of salts.

One is acid salt, the other is normal salt.

ACID SALT
the salt formed consist of H+ ion which gives acidic property.
eg.NaHSO4, KHCO3
這程況通常出現係當acid is in excess ,未能完全react完時。既然未react完，即係仲有H+ ion 剩下，therefore the remaining H+ ion will form acid salt.
H2SO4 + NaOH -> NaHSO4 +H2O
excess


NORMAL SALT
all the ionizable hydrogen atom is replaced (即係salt formed does not contain any H+ion)
eg. Na2SO4, K2CO3
相反，假如 NaOH is in excess, 即係所有H+ ion in acid will be completely reacted.咁冇哂d H+, 出來o既salt就唔會有presence of H+ ion.
H2SO4+ 2 NaOH ->Na2SO4 + 2H2O
excess

所以要睇出咩salt就要睇邊個reactant is 過量(in excess)

hope this helps ~~~