Question

Why is calcium carbonate relatively insoluble in water?

Answer 1

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

Explanation:

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`?