For this experiment, solid sodium ethanoate (or acetate CH3COONa·3H2O) and water in approximate mass ratio of 5:2 were mixed. In order to dissolve all of the salt, the mixture had to be heated. Upon cooling, some part of the salt should crystallize again and fall out of the solution at some point. In case of sodium ethanoate this typically does not happen by itself any time soon, as the solution lacks the so called crystallization centers, around which crystals could start to “grow”. A “supersaturated” solution is formed.
Extensive crystallization of sodium ethanoate started as soon as some crystals of the salt were introduced to the solution (the crystals act as crystallization centers) or the solution was poured over solid salt.
SOLUTIONS, pH: “Temperature dependence of salt solubility”