Question

I am working on a chemistry lab which involved recrystallization of Kw[Fex(C204)y(H20)z] (unknown ratios are a part of the rest of the lab) and was wondering about a few of these questions:

1) Another way to obtain crystals is to add 95% ethanol to an aqueous solution contains Kw[Fex(C204)y(H20)z]. Explain the chemical principle is being used in this crystallization technique.

2) If green crystals of the compound do not form, another technique that can be attempted is to reduce the volume of the solution. Explain how this procedure can enhance the probability of crystallization

Answer 1

For the crystallization procedure,

a) compound is soluble in aqueous medium but is insoluble in ethanol. Thus reprecipitation or reducing the solubility of compound in aqueous medium is done when we add 95% ethanol to the aqueous compound solution. This enables the crystals to form out of solution.

b) In the second method If the concentration of compound in solution is too low, crystallization will not proceed. Crystallization occurs when concentration is slightly below the saturation limit. Thus, concentrating or removal of some portion of solvent by evaporation would yield formation of crystals by saturation.