Why is sodium bisulfate acidic? [closed]








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So, as I know, the rule says that if you get a salt from strong acid and strong base it should be neutral. In this situation with sodium bisulfate and also trisodium phosphate we get an acid salt, although bought of them are produced from strong acid and strong base. Can someone explain why they have an acidic character and perhaps also give an explanation how I can determine if a salt will have an acidic character in water?




Sodium bisulfate $\ce{NaHSO4}$ has still one acidic hydrogen, as sulphuric acid is a diprotic acid, therefore it is acidic. By other words, just a half of sulfuric acid is neutralized here. Note that the anion $\ce{HSO4-}$ lays at boundary between strong and weak acids.


OTOH, trisodium phosphate $\ce{Na3PO4}$ is strongly basic, as hydrogenphosphate anion $\ce{HPO4^2-}$ is very weak acid.


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