Final answer:
A solution is unsaturated if it can dissolve more solute; it's saturated when it can't. A spoonful of salt dissolving in boiling water implies the solution was unsaturated. Undissolved solute at equilibrium indicates a saturated solution.
Step-by-step explanation:
When determining whether a solution is saturated or unsaturated, the key factor is the solution's capacity to dissolve additional solute. If a spoonful of salt is added to boiling water and it dissolves, this indicates that the original solution was unsaturated, as it was able to accept more solute. As more and more solute is added and it continues to dissolve, the solution remains unsaturated. However, when adding more solute results in no further dissolution, this would indicate that the solution has become saturated, meaning it contains the maximum amount of solute that can dissolve at that temperature and pressure.
In a saturated solution, any additional solute added will not dissolve and can lead to the presence of undissolved solute at the bottom of the container, showing that the solution has reached equilibrium. Conversely, an unsaturated solution is one that has not reached its solubility limit and is still able to dissolve additional solute. These concepts can be experimentally observed by adding a solute to a solvent and noting whether the solute continues to dissolve or not.