Supersaturated solutions are generally mixtures of a liquid solvent and a solid which dissolves (the solute).

Starting with pure water we can add crystals. Here I'm adding Sodium acetate (NaCH3COO) crystals which are very soluble. When we add the crystals we now have an aqueous solution (aq). We say the solution is unsaturated because we can still dissolve more crystals in the solution.

At some point no more crystals will dissolve at that temperature. The solution is said to be saturated. But we can heat the solution to a higher temperature and more will dissolve.

If we let the solution cool down, the extra solute (crystals) that dissolved remain dissolved in the solution. The solution is now supersaturated. But this is an unstable situation and if we add a seed crystal, or sometimes even just bump the solution, solid crystals will form and the solution will no longer be supersaturated.

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