Calcium sulfate (CaSO4) has limited solubility in water. 1 It is considered sparingly soluble in water, meaning that only a small amount of CaSO4 can dissolve in water under normal conditions.
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Why is CaSO4 sparingly soluble in water?
CaSO4, or calcium sulfate, is sparingly soluble in water due to its ionic nature and the structure of its crystal lattice. When a substance is sparingly soluble in water, it means that only a small amount of the compound can dissolve in water to form a solution.
Here’s why CaSO4 is sparingly soluble in water:
- Ionic nature: CaSO4 is an ionic compound composed of calcium ions (Ca2+) and sulfate ions (SO42-). 2 In the solid state, these ions are held together by strong ionic bonds. Water molecules are also polar and can interact with ions, but for CaSO4, the forces holding the ions together in the crystal lattice are stronger than the interactions between the ions and water molecules.
- Lattice energy: The crystal lattice of CaSO4 is highly stable due to the strong electrostatic interactions between the calcium and sulfate ions. Breaking these ionic bonds requires energy, known as lattice energy. This energy is much higher than the energy released when the ions interact with water molecules during dissolution. As a result, the solid CaSO4 tends to remain intact rather than dissolving in water.
- Ion-dipole interactions: When CaSO4 comes into contact with water, some ions at the surface of the crystal can interact with water molecules through ion-dipole interactions. 3 However, for the majority of the solid CaSO4, the internal ionic bonds prevent water molecules from penetrating the lattice and causing significant dissolution.
Overall, the combination of strong ionic bonding, high lattice energy, and limited ion-dipole interactions results in CaSO4 being sparingly soluble in water. As a consequence, only a small amount of CaSO4 will dissolve in water to create a dilute solution.
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- Calcium sulfate – Wikipedia. (2008, January 10). Calcium Sulfate – Wikipedia. https://en.wikipedia.org/wiki/Calcium_sulfate
- Cerritos.edu https://www.cerritos.edu/chemistry/chem_100/Handouts/100NAMINGPRACkeyS12.pdf
- Purdue.edu https://www.chem.purdue.edu/gchelp/liquids/iondip.html