Melting Point Determination

Melting Point - Melting Point Determination You will find that most of the products generated in your organic chemistry lab this semester are

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Melting Point Determination You will find that most of the products generated in your organic chemistry lab this semester are either white or yellow crystalline solids at room temperature. It can be difficult to tell them apart based solely on physical appearance. One of the first tasks that you will be assigned in lab this semester is to purify and correctly identify an unknown organic compound. There are many ways in which an organic unknown can be identified and we will touch on several methods during the course of the semester. Some of the more advanced techniques involve the use of expensive instrumentation such as IR and NMR spectrometers. These techniques offer us the most detailed information concerning the chemical makeup of a compound, but they are also very expensive and complex to utilize. Melting point comparison, on the other hand, offers a fine balance between ease of use and accuracy of information. All it requires is a simple apparatus and an accurate thermometer. The melting point of a chemical substance is the temperature at which its solid and liquid phases are in equilibrium. This week, you will be performing a melting point determination of an unknown solid and comparing it to known literature values in order to properly identify it. The melting points of most readily available chemical compounds are easily obtainable from any number of library and online resources. The CRC Handbook of Chemistry and Physics is an excellent source of physical data. It is imperative that you have accurate melting point values to compare your laboratory data to; otherwise your experiment will be an exercise in futility. Make sure that your table of reagents is filled out in its entirety prior to beginning your lab. A compound’s melting point range is defined by the temperature at which the sample first shows signs of melting (droplet formation within the pack of sample crystals) and the temperature at which the sample becomes fully liquefied (ie. Benzoic acid, 122-123 o C). A pure substance will exhibit a narrow melting point range (1-2 o C). As impurities are introduced into a sample, the melting point range of the parent compound will begin to change. Impurities have a twofold effect: they both broaden and depress (lower) the observed melting point range. A rough estimate of the purity of a mixed sample can be made via a comparison of the observed
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This note was uploaded on 01/29/2012 for the course CHEM 234-54 taught by Professor Morrison during the Fall '09 term at University of Georgia Athens.

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Melting Point - Melting Point Determination You will find that most of the products generated in your organic chemistry lab this semester are

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