Why does ethanoic acid react with calcium carbonate, while ethanol does not?

Question

kainui · Answer

Compare the pkas of ethanoic acid, ethanol, and carbonic acid and you'll see that ethanoic acid has a lower pka than carbonic acid does, so the ethanoic acid will lose its hydrogen while the carbonate will accept it as a base. This leaves you with calcium ethanoate and carbonic acid which is a weaker acid than ethanoic acid was, which should make some sense.

Similarly, this comparison between carbonic acid and ethanol shows that carbonic acid is more acidic than ethanol, so it stays rather than turning into carbonic acid with calcium ethoxide.

anonymous · Answer

can you relate carbonate with carbonic acid?

kainui · Answer

Carbonate is the conjugate base of carbonic acid.

kainui · Answer

Think of it as two things competing over which is more acidic.

So you will either have: Ethanoic Acid and Carbonate or Ethanoate and Carbonic acid depending on which one has the hydrogen. So then you compare, which acid is more acidic? The one that's most acidic will lose the hydrogen while the lesser of the two will have to take it.

aaronq · Answer

Overall, the answer provided is correct, but there is some confusion as to what's what and i'd like to clear that up.

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Protons from carbonic acid dissociate in two steps:
      $H_2CO_3\rightleftharpoons  HCO_3^-+H^+\rightleftharpoons CO_3^{2-}+H^+$

The first pKa of $H_2CO_3$ (carbonic acid) 3.6 is actually lower than that of ethanoic acid (4.76), while the second pKa (that of bicarbonate) (6.3) is higher than ethanoic acid. So carbonate will deprotonate ethanoic acid (as stated above). At the end you're left with salts of ethanoate and bicarbonate (not carbonic acid).

    $CH_3COOH +CO_3^{2-}\rightarrow CH_3COO^- +HCO_3^{-}$

anonymous · Answer

Thank you very much @aaronq