In experiment 2, recrystallization was used to purify the crude benzoic acid extracted from a mixture during experiment 1. Then a percent recovery for this recrystallization process was calculated. In experiment 3, the melting point ranges of the crude and purified benzoic acid were both determined by using Melt Temp Apparatus.
Recrystallization is a purification technique for non-volatile solids. The general idea of recrystallization is rely on the solubility of target product (as well as other impurities) and the temperature of solvent. The target material is dissolved in a hot solvent (in this case, hot water) and then solvent is slowly cooled down. Due to the solubility of a dissolved material decreases with decreasing temperature, the solution will become oversaturated and the solid will separate from the solution as it is cooled. Thus the mixture (crude benzoic acid) from experiment 1 can be separated. By looking into more details, the solution should be cooled down slowly after dissolvable solid mixture dissolved in solvent to ensure the purity of desired product. According to crystal lattice theory, when solid forms, it blocks impurities to form solid; thus recrystallization is possible.
Solubility is crucial in this experiment. There are three stages of solubility. Collision is when solid just added in solvent and nothing happens during collision stage; dissociation is when solvent attacks solids and part of the solids come off and mix with solvent; the last stage is solvation when solids completely dissolve in solvent thus two combines together.
In addition, picking a good solvent determines the success of this lab. The solvent needs to have high temperature coefficient so it can be heated to a high temperature. Then the solvent needs to have a boiling point less than the melting point of solid. This is crucial because solids... [continues]
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