[cliverlong]

Hi,

   Does anyone know a site where the mechanisms of standard high school / GCSE reactions are described?

e.g. reaction of CaCO₃ and HCl(aq) to make CO₂ gas, water and dissolved CaCl₂

Now I'm guessing wildly that an H⁺ from the acid is attracted to one O in the CO₃^2- because the O has a delta- charge (borrowing idea from organic)

This then weakens the C-O bond and the OH^- passes into solution (why?). The OH^- combines with another H⁺ from the acid to form the water from the acid (proportion depends on K_w)

Then limestone is now unstable CaCO₂²⁺ (is the charge correct? I am working on the basis the oxygen removed in the OH^- had an oxidation state of -2)

Then the Ca-O bond breaks (why?) and CO₂ passes out as gas.

The Ca²⁺ passes into aqueous solution.

The (2) Cl^- take no part in the reaction - they are only spectators from the acid that provided the H⁺ ions

So, I have accounted for the products and reactants and the quantities in the equation balance. (hooray!)

This "mechanism" seems plausible to me but might be complete nonsense.

Where can I check?

What methods are used to check proposed reaction pathways and mechanisms?

Thanks

Clive

[Borek]

No idea where to look for mechanism, but after protonation I would expect HCO₃^- to go into solution (remember calcium bis(hydrogencarbonate) is much better soluble then just calcium carbonate), where it is further protonated and then H₂CO₃ decomposes in the presence of water; I recall reading that H₂CO₃ molecule is quite stable on its own, but water catalyses decomposition.

[cliverlong]

No idea where to look for mechanism, but after protonation I would expect HCO₃^- to go into solution (remember calcium bis(hydrogencarbonate) is much better soluble then just calcium carbonate), where it is further protonated and then H₂CO₃ decomposes in the presence of water; I recall reading that H₂CO₃ molecule is quite stable on its own, but water catalyses decomposition.

That makes a lot of sense.

I like the argument via the solubility of hydrogen carbonate

then linking to the (reversible) disassociation of carbonic acid into water and carbon dioxide

Thanks

Clive