Orgo Lab Lecture 2 - Additional point to consider Eutectic...

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Additional point to consider: Eutectic point vs. melting point of pure compound: Similarity: Narrow Melting Range How do you tell what’s a eutectic point and a melting point of a compound? You just go by the melting range ( the difference) Difference: Eutectic point by definition is of the impure compound therefore the eutectic point is lower than the pure melting point and that’s how your going to be able to tell the difference, it will have a very narrow range but it will be lower than the pure point. Postlab: 1) remark on the purity of the sample based on melting range and accuracy You look at the melting point of the pure compounds and compare it to the one you took and if it matched then yes its pure, and if the range was narrow, if the melting point was lower or the range was narrow then you realize it’s not as pure as it should be even though it was supposed to be a pure sample. 2) statement on melting point and range for mixtures Mixtures by definition are impure and so you expect the melting point to be lower and the range to be wider. So say “ it is a mixture so the melting point is expected to be lower and the range to be wider”. 3) Melting point composition graph (draw and find eutetic point, eutectic temperature and composition) Eutectic Point Graph example is in continuation lecture. You will have two data points for every composition you took a melting point for. (watch lecture starting from 5:00 when drawing this 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 - 4) determination made too fast -5) criteria for filling melting point capillaries not adhered to
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Conclusion 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
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