Now, when it comes to K_sp calculations, realize that solubility is an equilibrium process. Hence calculations will require an ICE chart. So if you see K_sp within a question, that means you're most likely going to have to use an ICE chart. Now here with K_sp we have a formula we need to remember, so let's say that here we have our equation.

Again, K_sp deals with the solubility of ionic solids, which means that you're going to start out with an ionic solid. As you're reacting, we look to see how it breaks up into various ions. So let's say that it breaks up into some unknown number of B ions plus some unknown number of C ions. These are ions that they'd have charges, so I'm just going to write a random charge here for each one. Now, A, B, and C are your coefficients.

K_sp is an equilibrium constant and like all equilibrium constants, it equals products over reactants. However, remember we said K_sp deals with solids. Remember solids and liquids are ignored. So although K_sp equals products over reactants, like other equilibrium constants, the reactant will be a solvent, therefore it can be ignored. So K_sp simplify suggests equal to products.

Now, like other equilibrium constants, we'd have our products within brackets represent concentration, and then remember that their coefficients would become these powers. So that's how we break down the equilibrium expression for a K_sp value. So just remember it's equal to products over reactants. The reactant is a solid, so just drop it. So K_sp equals products.