Question

During a recrystallization procedure, if crystals do not form upon cooling to 0 °C:

i) Without changing the volume of the solution, what are three methods that can be used to induce nucleation (crystal growth)? Describe each method in one sentence (each).

ii) If none of your methods of inducing nucleation works (which you described in Part i), then what experimental steps would you take next in order to achieve recrystallization of the compound? Offer details. Assume that you do not have access to any more of the original mixture. Explain in two sentences or less.

Answer 1

1. Hydrothermal growth:
This is a type of growth from aqueous solution at high temperature (400-600 ºC) and pressure range (100-1000 atmosphere).

2.High temperature solution growth:
In hightemperature solutions, the constituents of the material to be crystallized are dissolved in a suitable solvent and crystallization occurs as the solution becomes critically supersaturated.

3.Temperature gradient method:
     Here, the transport of material from a hot region containing the source of the material to be grown, to a cooler region where solution is super saturated result in the formation of crystal growth.

Recrystallisation:

1. Find a suitable solvent for the recrystallization;
2. Dissolve the impure solid in a minimum volume of hot solvent;
3. Remove any insoluble impurities by filtration;
4. Slowly cool the hot solution to crystallize the desired compound from the solution;
5. Filter the solution to isolate the purified solid compound.