My old thread got locked due to inactivity.. Maybe the
moderators can merge this post into the old thread (last post on
2/10/10) to reduce repetition..
A quick question - what is the detriment of using iron
(II) chloride + carbonic acid to form iron (II) carbonate? Is it
because carbonic acid is a weak acid?
Hello again Gohby.
The method is unsuitable because the H+(aq) (from H2CO3, or HCl
if you use the equation FeCl2 + H2CO3 ---> FeCO3 + 2HCl) will
immediately react with any FeCO3(s) formed, to get back your
original reactants FeCl2(aq) and H2CO3, which decomposes into
CO2 and H2O.
Yes, in a way it is indeed because carbonic acid is a weak
acid, but your 'O' level student is unlikely to understand exactly
how this is related to why the method is unsuitable. Because the
acid is relatively weak, the conjugate base is relatively
strong, and consequently the carbonate ion base is readily
protonated to form carbonic acid, which exists in equilibrium with,
and hence decomposes into, carbon dioxide and water.
