Sulphur(iv)oxide is described as an acid anhydride. Elaborate on this statement?

1 Answer
anor277
Jun 9, 2018

Well, consider the reaction between #H_2O# and #SO_2(g)#...

Explanation:

#SO_2(g) +H_2O(l) rarr underbrace(H_2SO_3(aq))_(-=H_2O*SO_2)#

Sulfur dioxide is the acid anhydride of sulfurous acid, i.e. #H_2SO_3-=SO_2+H_2O#, i.e. the given acid LESS a fomula unit of water. While sulfurous acid can be deprotonated, often we can treat it as water saturated with sulfur dioxide, i.e. as #H_2O*SO_2# (which is of course formally #H_2SO_3#), The smell is sulfurous, but many people (including me!) find it pleasant, and antiseptic.

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