We will be conducting a crystallization experiment this week. I was wondering what the most common materials used for this experiment are and what are their best solvents.
Thanks from Sheryl
alum in water is really good, however, it takes some time for the water to evaporate.
I have done a fractional crystallization using KClO3 and CuSO4*5H2O. It is possible to obtain WHITE KClO3 (not blue from contaminating CuSO4).
1. Why is the final product from the crystallization process isolated by vacuum filtration and not by gravity filtration? 2. Environmentally speaking, what are the advantages and disadvantages of recrystallization versus column chromatography? Recrystallization –Report Form
3. Explain, in your own words, why dissolving and then reforming crystals improves the purity of those crystals. 4. Explain why a solvent that can dissolve the solute, even when it is cold, is useless for recrystallizations.
The vacuum produces a lower pressure which cools the solution and promotes crystallization. Also, it dries the crystal well. When you are using a vaccum, you decrease the pressure from the lower side of the filter, keeping a big pressure difference which makes the solvent pass through the filter quickly, regardless of the amount of solution above the filter.
This way you minimize the residual amount of solvent in your solid product, but also avoid losses due to temperature increase. Vacuum filtration is used instead of gravity filtration in order to achieve a dryer product in less time. The faster process of vacuum filtration allows the slurry to remain cold and in cases such as with benzoic acid more crytals will remain formed at colder temperatures.
When it comes to crystallization experiments, there are various materials that can be used, depending on the desired outcome. Two commonly used materials are alum (potassium aluminum sulfate) and KClO3 (potassium chlorate).
For alum, the best solvent is water. You mentioned that alum in water is effective, but it takes some time for the water to evaporate. This is because the solubility of alum decreases as the temperature drops, leading to the formation of crystals. To speed up the evaporation process, you can increase surface area by using a shallow dish or stirring the solution gently.
In the case of KClO3, the best solvent is also water. However, to obtain white KClO3 crystals without any contamination from the blue CuSO4, a technique called fractional crystallization can be used. This involves dissolving both compounds in water at an elevated temperature until they are fully dissolved. Then, gradually lower the temperature to allow KClO3 to crystallize first while CuSO4 remains in solution. The resulting KClO3 crystals can be separated from the solution using filtration or other suitable techniques.
It's important to note that safety precautions should be followed when working with potentially hazardous materials like KClO3. Always refer to the specific procedures and guidelines provided by your instructor or lab manual to ensure the experiment is conducted safely and effectively.