Why does barium sulphate not dissolve in HCl while barium sulphite does? 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?
$\ce{BaSO_3}$ 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  : $$\ce{BaCO_3 + 2 H^+ -&gt;  Ba^{2+} + CO_2(g) + H_2O}$$
$$\ce{BaSO_3 + 2 H^+ -&gt; Ba^{2+} + H_2O + SO_2(g)}$$ 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.