Once equilibrium establishes, we're given that the KSP or the Solubility product is equal to 1.0 times ten to negative ten at 25 degrees Celsius. So we want to find the solubility of barium sulfate. To find the solubility of barium sulfate, we must first write the dissociation reaction for barium sulfate. Therefore, we get 1 mol of barium sulfate in its solid form, dissociates into 1 mol of barium plus 1 mol of sulfate, and both guys are in the Aqueous form. The first step is to write the KSP equation. To write the KSP equation, we simply realize that this guy is a solid and therefore he doesn't count.