illöslighet

Illöslighet is a term used in chemistry to describe the inability of a substance, typically a solid, to dissolve in a solvent. This is in contrast to solubility, which is the capacity of a solute to dissolve in a solvent to form a homogeneous solution. When a substance exhibits illöslighet, it means that even when mixed with a solvent, it will not disperse evenly and will likely settle out or remain as distinct particles.

The concept of illöslighet is related to intermolecular forces. For a substance to dissolve, the attractive forces between the solute particles must be overcome by the attractive forces between the solute and solvent particles. If the solute-solvent interactions are significantly weaker than the solute-solute interactions, the solute will tend to remain undissolved, exhibiting illöslighet. Similarly, if the solvent-solvent interactions are very strong and resist the introduction of solute particles, illöslighet can also occur.

Several factors can influence whether a substance is considered illösligt. Temperature and pressure can play a role, though for most solids in common solvents, the effect is less pronounced than for gases. The specific chemical nature of both the solute and the solvent is paramount. For instance, a highly polar solute like salt is illösligt in a nonpolar solvent like oil, and vice versa.

While a substance might be described as illösligt, it's important to note that complete and absolute illöslighet is rare. Most substances have a very low, but non-zero, solubility. Therefore, the term often implies a practical absence of dissolution under normal conditions, meaning that the amount that does dissolve is negligible for most purposes. In laboratory and industrial settings, identifying illöslighet is crucial for processes like separation and purification.