Question: Consider a body of water in equilibrium with solid calcium sulfate (CaSO4), for which Ksp = 4E-5 at 25 degrees Celsius. Calculate the solubility of calcium sulfate in water (in grams/liter) assuming that the other reactions are negligible.
Here you are dealing with an equilibrium situation. CaSO4 is considered to be an insoluble salt, but when a salt (or any solid) is placed in water (or other liquid) some dissolving typically occurs. Initially, some of the calcium sulfate dissolves in the water. But this process of course creates calcium and sulfate ions that can recombine to form the solid. For insoluble substances, this reverse process is much more favored ...
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