The solubility of calcium sulfate in water, specifically for its dihydrate form (gypsum), is 0.26 grams per 100 milliliters at 25 °C.
Calcium sulfate (CaSO₄) is considered sparingly soluble in water, meaning that while it does dissolve, its solubility is relatively low compared to many other salts. Its different forms exhibit slightly varying solubility characteristics.
Calcium sulfate exists in several forms, most notably as anhydrous calcium sulfate (anhydrite) and calcium sulfate dihydrate (gypsum). The solubility in water typically refers to the dihydrate form, which is common and stable under normal environmental conditions.
Key Solubility Information
The provided reference details the solubility of calcium sulfate dihydrate:
| Property | Value | Form | Temperature |
|---|---|---|---|
| Solubility in Water | 0.26 g/100ml | Dihydrate | 25 °C |
Solubility Product (Ksp)
Beyond direct mass solubility, the solubility of calcium sulfate can also be described by its solubility product constant (Ksp). The Ksp value indicates the extent to which a sparingly soluble ionic compound dissolves in water. A smaller Ksp value generally means lower solubility.
Here are the Ksp values for different forms of calcium sulfate from the reference:
- Anhydrous Calcium Sulfate (CaSO₄): 4.93 × 10⁻⁵ mol²L⁻²
- Calcium Sulfate Dihydrate (CaSO₄·2H₂O): 3.14 × 10⁻⁵ mol²L⁻²
These Ksp values further illustrate the limited solubility of calcium sulfate in water, indicating that it does not dissociate extensively into calcium ions (Ca²⁺) and sulfate ions (SO₄²⁻) in solution.
Practical Implications
The low solubility of calcium sulfate has several practical implications:
- Hard Water: Calcium sulfate is a major component contributing to permanent hardness in water, as it cannot be removed by boiling.
- Industrial Uses: Its low solubility makes it useful in materials like plaster of Paris (a hemihydrate form of calcium sulfate), where controlled hydration and setting are crucial.
- Environmental Impact: In geological contexts, its dissolution and precipitation play a role in the formation of evaporite deposits and can affect groundwater chemistry.
For more detailed information, you can refer to the Wikipedia article on Calcium Sulfate.
