Sodium acetate is a common example used in general chemistry lectures to illustrate the idea of supersaturation, and that precipitation of a supersaturated solution can be initiated by a seed crystal. It makes a great demo, and there are many excellent videos online that illustrate this phenomenon.

My question is: What is it about sodium acetate that makes it so well-suited to this particular demonstration? Is there an explanation from experiment, theory, or simulation that explains why sodium acetate is better than, say, sodium chloride? (Or perhaps potassium acetate? though that may be a cost issue.)

  • 3
    $\begingroup$ Beside NaOAc (used in hand warmers), super cooling the melt of benzoic acid is an other attractive example, too. It is not obvious if the presence of a second type of (solvent) molecules eventually helps or hampers the crystallization (e.g., viscosity, kinetics vs. thermodynamics). On top, conditions favourable to create (microscopic) germs of crystallization may differ from those of crystal growth (e.g., here. $\endgroup$
    – Buttonwood
    Commented Dec 19, 2021 at 10:39
  • 1
    $\begingroup$ Good question! As @Buttonwood states, viscosity plays a major role. Consider that silicate glasses (e.g., soda-lime or "window" glass) devitrify (recrystallize) if heated for a long time and allowed to cool slowly -- and at these temperatures, glass is very viscous. See franklin.chem.colostate.edu/glassguy/devit.html $\endgroup$ Commented Dec 19, 2021 at 22:32
  • $\begingroup$ I think it would be interesting to consider the nature of the activation barrier to crystallization. Is the activation barrier mostly entropic or enthalpic? If I had to guess, I would think it is an entropic bottleneck, where it is difficult to induce the necessary molecular rearrangements to generate critical nuclei of the crystal. $\endgroup$
    – scmartin
    Commented Feb 10, 2023 at 20:56


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.