Final answer:
The solute when stirring salt in water until it disappears is the salt (NaCl). The process forms a saline water solution and can reach a point of solubility equilibrium, represented by a saturated solution.
Step-by-step explanation:
When stirring salt (NaCl) in water until the salt disappears, the solute in this situation is the salt itself. Dissolving the salt into water forms a saline water solution. Initially, the water (the solvent) causes the ionic compound sodium chloride to dissociate into its individual sodium and chloride ions, which become surrounded and hydrated by water molecules. As you continue adding salt, it will dissolve up to a certain point. Eventually, you may reach a state where no additional salt will dissolve, resulting in a saturated solution. This state represents a point of solubility equilibrium, where the processes of dissolution and recrystallization happen at the same rate, maintaining a constant concentration of dissolved salt in the solution. Beyond this point, any added salt will remain undissolved at the bottom of the container.