Crystallization (or recrystallization) is the most important method for purification of organic compounds . The process of removing impurities by crystallization involves dissolving a compound in an appropriate hot solvent, allowing the solution to cool and become saturated with the compound being purified, allowing it to crystallize out of the solution, isolating it by filtration, washing its surface with cold solvent to remove residual impurities, and drying. [1] X Research source
This is best done in a controlled chemistry laboratory, in a well-ventilated area. Note that this procedure has wide applications, including large scale commercial purification of sugar by crystallization of the raw sugar product which leaves impurities behind. [2] X Research source
Steps
Community Q&A
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QuestionWhy should warm pentane and ether solutions not be suction filtered?Community AnswerBoth are highly volatile and will boil into the aspirator or vacuum pump trap.
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QuestionHow do I start the crystallization of sugar?Gideon JamesCommunity AnswerIt starts with two major events: nucleation and crystallization. Clarified sugar cane juice is boiled in evaporators, which leaves a thick syrup. The syrup is then boiled at low temperatures, the seeding is added, and the product is then put in a centrifuge to separate the crystalline sugar and molasses. The seeding is what is most important, since that produces the nuclei.
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QuestionWhich compound is the best for crystallization?NSEasternShoreChemistCommunity AnswerIf you want to practice, benzoic acid. It's very soluble in boiling water and very insoluble in ice-cold water. It's also rather nontoxic and no flammable solvents are involved.
Tips
- If too little solvent is used, crystallization may occur too quickly when the solution is cooled. When crystallization occurs too quickly, impurities may become trapped in the crystals, defeating the purpose of purification by crystallization. On the other hand, if too much solvent is used, crystallization may not occur at all. It is best to add in just a little more solvent beyond saturation at the boiling point. Finding the right balance will require practice.Thanks
- When trying to find the ideal solvent by trial and error, start with the low-boiling, more volatile solvents first, as they can be removed more readily.Thanks
- Perhaps the most important step is waiting for the hot solution to cool slowly and allow crystals to form. It is extremely important to be patient and allow the solution to cool undisturbed.Thanks
Things You'll Need
- Organic compound for crystallization
- An appropriate solvent
- Test tubes or reaction containers
- Glass stirring rod
- Wood applicator stick, or porous porcelain boiling chips
- Activated charcoal (carbon)
- Steam bath or hot plate
- Erlenmeyer flasks
- Stemless funnel
- Fluted filter paper, and non-fluted for vacuum
- Pipettes
- Hirsch or Buchner funnel apparatus
- Watch glass
References
- ↑ https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book%3A_Organic_Chemistry_Lab_Techniques_(Nichols)/3%3A_Crystallization/3.1%3A_Overview_of_Crystallization
- ↑ https://www.gvsu.edu/labsafety/ventilation-70.htm
- ↑ http://www.wiredchemist.com/chemistry/instructional/laboratory-tutorials/recrystallization
- ↑ http://ccc.chem.pitt.edu/wipf/Web/Crystallization%20Solvents.pdf
- ↑ https://www.chemistryviews.org/details/education/2538901/Tips_and_Tricks_for_the_Lab_Growing_Crystals_Part_2.html
- ↑ https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matter/Solutions_and_Mixtures/Case_Studies/RECRYSTALLIZATION
- ↑ https://orgchemboulder.com/Technique/Procedures/Filtration/Filtration.shtml
- ↑ http://www.orgchemboulder.com/Technique/Procedures/Crystallization/Crystallization.shtml
- ↑ http://web.mnstate.edu/jasperse/Chem355/Recrystallization-1.doc.pdf
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