How can crystallization be initiated in a supersaturated solution

The salt resting at the bottom of the pot will provide a site for nucleation to occur. Primary nucleation is the first step in crystallization. Simply defined, it's the growth of a new crystal.

On an industrial scale, a large supersaturation driving force is necessary to initiate primary nucleation. The initiation of primary nucleation via this driving force is not fully understood which makes it difficult to model experiments are the best guide. Usually, the instantaneous formation of many nuclei can be observed "crashing out" of the solution.

You can think of the supersaturation driving force as being created by a combination of high solute concentration and rapid cooling. In the salt example, cooling will be gradual so we need to provide a "seed" for the crystals to grow on.

In continuous crystallization, once primary nucleation has begun, the crystal size distribution begins to take shape. There are a few other methods that can be used to initiate crystallization when scratching fails:. Lisa Nichols Butte Community College. Complete text is available online. By pulling the end of the stemit will be removed from the prepared ampoule. The ampoule with the solution should be left to cool slowly.

Do not force the cooling with water or any kind of cooling spray. After the system-ampoule is cooled down, the crystallisation can be initiated by cutting the stem Fig. The cutting should be done slowly to leave the solution in a short contact with the metal of the scissors. Using a thermometer the exothermic reaction can be demonstrated quantitatively Fig. Observation and discussions The solutions can contain variable amount of dissolved substance and depending on it one can observe three cases: a An unsaturated solution is one that has not dissolved as much solute as possible at a given temperature.

If you add more solute to an unsaturated solution it will dissolve. What else happened when recrystallization took place? Review How do we know a solution is supersaturated?

How can we cause recrystallization of a supersaturated solution? What does the seed crystal do? Licenses and Attributions. CC licensed content, Shared previously.