Occlusion
Definition and meaning of Occlusion in chemistry.
Occlusion is a specific type of coprecipitation in which impurities become trapped within the growing crystal lattice of a precipitate. This phenomenon occurs when foreign ions or molecules are enclosed by the rapidly forming layers of the crystal.
In more detail
During precipitation, if crystal growth happens too quickly, impurities adsorbed on the surface can be covered by subsequent layers of the primary substance. Unlike solid solution formation, the occluded impurities are physically trapped in pockets or imperfections within the crystal rather than substituting for ions in the regular lattice. This process can significantly contaminate analytical precipitates, leading to errors in gravimetric analysis. Digestion or slow precipitation can help minimize occlusion.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Classification | Type of coprecipitation |
| Mitigation Strategy | Digestion or slow precipitation |
When precipitating barium sulfate (BaSO4) rapidly, potassium ions (K+) from the surrounding solution can be occluded within the BaSO4 crystals, artificially increasing the mass of the precipitate.
Frequently asked questions
How can occlusion be minimized in the laboratory?
By precipitating slowly from dilute, hot solutions and allowing the precipitate to digest.
What is the difference between occlusion and inclusion?
Occlusion traps impurities in crystal defects or pockets, while inclusion substitutes impurities directly into the crystal lattice.