To my knowledge, sulphuric acid is produced by complex industrial processes like contact process.

The following structure shows a sulphate ion.

enter image description here

I wonder why sulphuric acid cannot be produced through the protonaction of sulphate ions, for example, by mixing HCl and Na2SO4.

After mixing the salt and acid, concentrated sulphuric acid can be produced by heating up the liquid.

However, this method is not commonly used, or not even used, why?

  • $\begingroup$ What are the costs of hydrochloric acid and sulfuric acid, per mole of protons? $\endgroup$ Nov 9, 2023 at 14:49
  • 5
    $\begingroup$ What are you going to use to doubly protonate sulfate ion? It needs to be a stronger acid than sulfuric, there aren't many and HCl is not one of them, they are all more expensive than bulk sulfuric. $\endgroup$
    – Waylander
    Nov 9, 2023 at 14:49
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    $\begingroup$ Why? Because the reaction you mention works in the opposite way. It's $$\ce{2NaCl + H2SO4 -> HCl(g) + Na2SO4}$$ $\endgroup$
    – Mithoron
    Nov 9, 2023 at 16:00
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    $\begingroup$ Most sulphate salts are produced from sulfuric acid, so converting them back is hardly an efficient process. $\endgroup$
    – matt_black
    Nov 9, 2023 at 17:07

1 Answer 1


Sulfuric acid is too strongly dissociating to be extracted from water solution in this way.

With sulfuric acid you have complete dissociation for the first stage (in strongly acidic solution) forming solvated $\ce{H^+}$ and $\ce{HSO4^-}$. You will have these in combination with the sodium and chloride ions.

With this solute composition, the boiling-down stage will likely produce sodium bisulfate ($\ce{NaHSO4}$) plus $\ce{NaCl}$ and fumes containing unreacted (or re-formed) $\ce{HCl}$.

  • $\begingroup$ But than you could keep heating the sodium bisulphate and eventually produce sulphur trioxide which you could hydrolyse to sulphuric acid :) $\endgroup$
    – Tom P
    Nov 12, 2023 at 10:15

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