Water’s unique polarity—two hydrogen atoms bonded to a larger, negatively charged oxygen atom—creates a net dipole that allows it to form hydrogen bonds with itself and with solute molecules.
When a solute such as sugar or salt is added, water molecules surround the solute particles, pulling them apart. As more solute is added, the water eventually reaches a point where all available sites are occupied; at that moment the solution is saturated.
To exceed the saturation point, heat the solvent to near its boiling temperature. The increased kinetic energy expands the spaces between water molecules, letting additional solute dissolve. Continue adding the solute while stirring until no more will dissolve, even though the saturation point has been surpassed.
Remove the heat and allow the solution to cool slowly. The excess solute remains dissolved for a short time, forming a metastable, supersaturated solution that is highly prone to crystallization when disturbed.
One classic demonstration uses sodium acetate. A supersaturated sodium acetate solution can be triggered to crystallize instantaneously by introducing a single seed crystal, producing “hot ice” – ice‑like crystals that simultaneously release heat.
Similarly, a hot sugar solution can be cooled while a string or needle is suspended in it. Over time, sugar molecules accumulate on the surface, forming a large, edible crystal—commonly known as rock candy. Enjoy responsibly and remember to maintain good dental hygiene, as excessive sugar consumption can lead to cavities.
