Intuition tells me that the ionic bond in the sulphate must be stronger than that in the sulphite.

Is this true?

If it is then why? The charge on the barium ion is 2+ in both cases and the charge on the sulphate and sulphite ions are both 2-.

The sulphate has an extra oxygen atom. It's presence is somehow making the ionic bond stronger. But how/why?

  • 2
    $\begingroup$ Do you know about the reaction of sulfites and acid? $\endgroup$
    – Ed V
    Commented Jun 20, 2020 at 19:47
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    $\begingroup$ The bond is pretty much the same. That's not where the explanation lies. $\endgroup$ Commented Jun 20, 2020 at 20:25
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    $\begingroup$ Consider sulphurous acid ( rather SO2(aq)) acidity constants pKa1=1.857, pKa2=7.172. As consequence, the BaSO3 solubility in HCl is high, as SO3^2- concentration is low. $\endgroup$
    – Poutnik
    Commented Jun 20, 2020 at 21:18
  • 1
    $\begingroup$ Strongly related: chemistry.stackexchange.com/questions/115827/… $\endgroup$ Commented Jun 21, 2020 at 3:54
  • 2
    $\begingroup$ and chemistry.stackexchange.com/questions/17271/… $\endgroup$ Commented Jun 21, 2020 at 3:55

1 Answer 1


$\ce{BaSO_3}$ has the same property as $\ce{BaCO_3}$ : When reacting with an acidic solution, these two substances produce a gas which can get out of the solution, and displaces the equilibrium to the right : $$\ce{BaCO_3 + 2 H^+ -> Ba^{2+} + CO_2(g) + H_2O}$$ $$\ce{BaSO_3 + 2 H^+ -> Ba^{2+} + H_2O + SO_2(g)}$$ This allows these two substances to be soluble in $\ce{HCl}$ solutions. As a contrary $\ce{BaSO_4}$ has not this possibility to produce a gas in an acidic solution : it is and remains insoluble in $\ce{HCl}$ solutions.


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