Solubilization Model for Ionic Compounds
This Demonstration considers a model for the solubilization of an ionic compound in water.[more]
According to the most popular models, which are consistent with spectroscopic measurements, the crystal ions in the vertex positions are the first to dissolve. Those on the corners do not react as easily with water molecules and those on the faces have almost zero probability of reacting. However, whenever an ion is removed, new vertices are created.
In this Demonstration, you can change the probability of the site where the next dissolution occurs. The crystal is idealized as a cube in which the anions are shown in red and cations in blue. The "vertex odds" and "corner odds" controls vary the probability of a dissolution at one such site. The bar chart on the left shows the resulting distribution of probability.[less]
Snapshots 1, 2, 3: solubilization takes place mostly on the ions in the vertex/face/corner positions
The following images are some photos taken during an experiment in our laboratory. We used a micropipette to inject water onto a single crystal of sodium chloride (∼0.1 mm side). The first photo shows a dazzling white crystal as a consequence of the scratches on the surface, and the first effect of the water is to smooth the surface, making it transparent. Subsequently, the solubilization starts.
 S. Coluccia, S. Lavagnino and L. Marchese, "The Hydroxylated Surface of MgO Powders and the Formation of Surface Sites," Materials Chemistry and Physics, 18(5–6), 1988 pp. 445–464. doi:10.1016/0254-0584(88)90016-8.