Why is calcium carbonate relatively insoluble in water?

1 Answer
Dec 7, 2015

Simply because the electrostatic bonds between the carbonate anion and the calcium ion are too strong to be overcome by solvation by water molecules.


In fact most carbonates are insoluble in water (the exceptions are?). Carbonate is a doubly charged negative ion that should form strong electrostatic bonds with metal ions - the doubly charged calcium ion, #Ca^(2+)#, should form strong ionic bonds, and indeed it does.

As physical scientists, however, we seek actual data, and I confess that I cannot find an appropriate table. I did find #K_(sp) = 3.3 xx 10^-9#, which corresponds to approx. 10 mg per litre at #25# #""^@C#.

Should the #pH# of the solution be increased, would you expect the solubility of calcium carbonate to go up or down? Will the carbonate ion remain as carbonate at lower #pH#?