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Recrystallization

Estopace, Edgie1, Polintan, Clarisse K.

Professor Edgie Estopace, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology; Clarisse Polintan, CHM145L/A21, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology

ABSTRACT
This experiment is all about identifying the appropriate solvent for recrystallization and technique and to use the recrystallization technique in purifying a solid sample. Most organic substances are impure and require techniques in order to purify a sample. One of these techniques to make an impure sample pure is by recrystallization. This experiment includes the determination of a good solvent for recrystallization for compounds such as: acetanilide, acetamide, aspirin, benzoic acid, naphthalene, and sucrose, for solvents such as: water, ethanol, benzene, and ethyl acetate. Also pure acetanilide is achieved. here are five major steps in the recrystallization process: dissolving the solute in the solvent, performing a gravity filtration, if necessary, obtaining crystals of the solute, collecting the solute crystals by vacuum filtration, and, finally, drying the resulting crystals giving us the pure sample of the compound. The best solvent used for each of the compounds listed and the percentage recovery of the crude acetanilide. The physical properties of the compound were also determined.

INTRODUCTION
Differential solubility is defined as the differences in the amount of solid that can be dissolved in an appropriate solvent as affected by variations in temperature. Solubility is inversely proportional to its temperature, since most solids have solubilities that are lower in liquid solvents at low temperatures. Differences in solubilities are sometimes used in the process of obtaining pure compounds by dissolving the solid in hot solvent and allow the undissolved impurities to be filtered off. The filtrate would then be cooled down and recrystallized as a purer compound. There should be differences in the solubilities of the solid and the impurities in order for the recrystallization to be effective. Recrystallization only works when the proper solvent is being used. The appropriate recrystallization solvent should: dissolve the entire compound at high temperature, dissolver very little or none of the compound at low temperature, have different solubilities for the compound and the impurities, have a boiling point below the melting point of the compound, have relatively low boiling point, be inert with respect to the compound, and be relatively inexpensive.

MATERIALS AND METHODS
The first part of the experiment required the students figure out which solvent is appropriate for recrystallization technique. Approximately 0.10 grams of acetamide was weighed and placed inside a test tube. The acetamide was then dissolved in two millilitres of cold water. The solubility behaviour was then observed. If the acetamide did not dissolve, the mixture was then boiled and it’s solubility behaviour was again observed. These steps were then repeated but with cold ethanol, benzene, and ethyl acetate as the solvent instead of water.

The above procedures were repeated, however, the students used different solutes this time for observation. The compounds used next were acetanilide, aspirin, benzoic acid, naphthalene, and sucrose, followed by the recording of data. The second part of the experiment tackled the recrystallization process using impure acetanilide and water as a solvent to obtain a pure sample of acetanilide. This part used the Hot Gravity Filtration Set-up first, followed by the Vacuum Filtration Set-up. The Hot Gravity Filtration Set-up included the following apparatuses: a stemless funnel, a fluted ashless filter paper, an Erlenmeyer flask, a hot water bath, and a hot plate. The Vacuum Filtration Set-up included water suction, rubber tubing, a 500ml Erlenmeyer flask, a rubber stopper and a porcelain...
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