Posting 04 - Recrystallization Lecture Outline

Posting 04 - Recrystallization Lecture Outline - Additional...

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Copyright © 2016 Govindarajoo, G. Rutgers, The State University of New Jersey. All rights reserved. Additional points to consider: Eutectic point vs. melting point of pure compound: Similarity: Difference: What to consider when determining identity of unknown: What is the first set of If you were given a choice, would you pick standards with Why? What does an Postlab: 1) remark on the purity of the sample based on melting range and accuracy 2) statement on melting point and range for mixtures 3) Melting point composition graph (draw and find eutetic point, eutectic temperature and composition) Eutectic Point Graph 4) Identifying unknown and reasoning 5) Sources of Errors (you will need this section for every experiment) Why some melting points may not have agreed with literature melting points -1) moisture in the air absorbed by the sample - 2) contamination of the sample - 3) thermometer in Melt-Temp not calibrated - only instance where melting point could be - 4) determination made too fast -5) criteria for filling melting point capillaries not adhered to Conclusion
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Copyright © 2016 Govindarajoo, G. Rutgers, The State University of New Jersey. All rights reserved. Essentially, did you achieve your purpose (look at your brief statement of purpose for prelab)? State what the eutectic temperature and composition at eutectic point was for your mixture of urea and cinnamic acid. State what your unknown was. Recrystallization Experiment Crystallization Sketch of apparatus: Fig. 4.1, 4.3, 4.15 Crystallization: a method to purify solids 4 important concepts to consider in the process of recrystallization - solubility - saturation level - exclusion - nucleation Read details on how these concepts are employed and what is involved on pg. 61 Example of crystallization in the human body: kidney stones Most common component is calcium oxalate Soluble in urine and blood Saturation level goes up with low urine volume, high concentration of stone promoters Nucleation on calcium phosphate (hetereogeneous nucleation) presents a Impurities in solids can result from reactions: -side products, unreacted starting materials, inorganic materials, solvents From storage: - decomposition, contamination from other chemicals Impurities may be trapped within the crystal lattice or on the surface of the solid.
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