Calcium sulfate (CaSO4) is slightly soluble in water, meaning that only a small amount of the compound dissociates into its constituent ions (Ca2+ and SO42-) when dissolved.
Here's a breakdown of its solubility behavior:
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Partial Dissociation: While calcium sulfate is an ionic compound, its attraction between the calcium and sulfate ions is strong enough that not all of the compound breaks apart into ions when in contact with water.
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Equilibrium: When calcium sulfate is placed in water, a dynamic equilibrium is established:
CaSO4(s) ⇌ Ca2+(aq) + SO42-(aq)
This means that some calcium sulfate dissolves, but the ions can also recombine to form solid calcium sulfate. At equilibrium, the rate of dissolution equals the rate of precipitation. -
Solubility Product (Ksp): The solubility of calcium sulfate is quantified by its solubility product (Ksp). The Ksp is the equilibrium constant for the dissolution reaction. For calcium sulfate, the Ksp value indicates its limited solubility. A higher Ksp means greater solubility.
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Factors Affecting Solubility: Several factors can influence the solubility of calcium sulfate:
- Temperature: Solubility generally increases with temperature, though this effect can be complex for calcium sulfate.
- Presence of Other Ions: The presence of other ions in the solution, particularly those that can form complexes with calcium or sulfate ions, can affect solubility. For example, the common ion effect can decrease the solubility of calcium sulfate if calcium or sulfate ions are already present in the solution.
In summary, calcium sulfate dissolves in water to a limited extent due to the strong ionic bonds within the compound and the establishment of an equilibrium between the solid and dissolved ions. It is classified as slightly soluble, not fully soluble or insoluble.
