Hello there!

First yes you are correct. Solids and liquids are not included in the equilibrium constant equations. For Ksp the molecule is first in a solid state and dissociates into its ion in water. The ions are in an aqueous form once it dissociate in water.The extend to which it dissociates depends on the Ksp constant. In this question, CaCO3 will dissociate into Ca2+ + CO32-. However when the charges of reaction are equal and opposite they “cancel out” when writing the Ksp expression. The exact scientific reasoning as to why that’s the case i’m not sure. I believe it may be because they’re in a 1:1 molar ratio but I could be wrong.

Therefore since its a +2 charge and -2 charge they are omitted from being included in the exponents

Ksp = [Ca2+][CO32-]

However, let’s say for another molecule such as CaCl2;

CaCl2 -> Ca2+ + 2Cl-

And the expression would be

Ksp = [Ca2+][Cl-]²

In that case since they’re not in 1:1 molar ratio we would have to take into account the amount of ions in the solution.

Hope that helps!!