Melting Point and Recrystallization

2886 WordsNov 29, 201212 Pages
Recrystallization and Melting Point of Benzoic Acid Organic Chemistry 1 10/4/12 Abstract Recrystallization was done to remove impurities from the sample. The percent recovery of benzoic acid during recrystallization is 23.02%. The difference between the pure and impure samples was observed by comparison of melting points. It was found that impure sample had a lower and wider melting point range of 120.1-122.2 (C). The pure sample melting point range was 121.3-122.5 (C). These ranges helped determine purity by comparing the known melting point of pure benzoic acid. Introduction Most of the organic substances recovered from organic reactions are impure and require purification to obtain the desired pure product. The extracted benzoic…show more content…
If the solute melts prior to the boiling of the solvent, recrystallization will not be able to occur. For example, if you wanted to purify a sample of Compound X which is contaminated by a small amount of Compound Y, an appropriate solvent would be one in which all of Compound Y dissolved at room temperature because the impurities will stay in solution and pass through filter paper, leaving only pure crystals behind. Also appropriate would be a solvent in which the impurities are insoluble at a high temperature because they will remain solid in the boiling solvent and can then be filtered out. Finally, the solvent should be volatile enough as to evaporate from the surface of the compound and be of low financial cost. Impurities can be removed by adding charcoal to the solution and hot gravity filtration. Adding charcoal provides a charged surface that is able to absorb impurities. The impurities that were absorbed by the charcoal were trapped in the filter paper during hot gravity filtration. Hot gravity filtration is the process by which the solution is filtered while on top of a heat source, such as a steam bath. This will remove any insoluble impurities (like charcoal used to remove the methyl orange) from the solution while maintaining the high temperature and high solubility coefficient of the solution. This prevents the solid from crystallizing from the solution while within the filtering apparatus.
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