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Unformatted text preview: EXPERIMENT #1 SOLUBILITY TESTS AND RECRYSTALLIZATION INTRODUCTION The preparation of compounds in as pure a state as possible is a crucial aspect of organic chemistry. Techniques used for this purpose include the recrystallization of solids, the distillation of liquids, and chromatography. In this laboratory session, you will purify salicylic acid by recrystallization from an appropriate solvent after examining the solubility of some typical organic compounds in various common laboratory solvents. OVERVIEW OF THE EXPERIMENT This experiment has two parts: Part I: Solubility tests of various compounds in various solvents to help reinforce the concept of "like dissolves like". Part II: the purification of an organic compound by recrystallization and the use of decolourizing charcoal. EXPERIMENTAL PROCEDURE Part I. Solubility tests The five compounds to be tested are anthracene, benzoic acid, phthalic acid, resorcinol and the sodium salt of 1-naphthylamine-4-sulfonic acid (sodium naphthionate). The solvents to be used are ligroin (an alkane mixture which behaves like hexane), toluene, ethanol and water. Structures of these compounds and solvents are shown below. Naphthionate Sodium OH O OH OH O O OH HO NH 2 OH H 2 O Anthracene Benzoic Acid Phthalic Acid Resorcinol Ethanol n-Hexane Water Toluene SO 3 Na Each compound is to be tested in each solvent using the procedure indicated below. For each test determine whether the compound is soluble in the cold solvent, and, if not, whether it is soluble when the solvent is heated. Add ~ 100 mg (a spatula tip) of each compound to separate dry test tubes. Add ~ 3 mL of solvent, using the calibrated pasteur pipettes provided. Take care not to contaminate the solvent bottle. If the solute does not dissolve, heat the test tube carefully, using the steam bath. If the solid dissolves completely, it may be considered soluble in the hot solvent; if some but not all dissolves, it may be recorded as moderately soluble, and further small amounts of solvent should be added with heating until solution is complete. Cool the hot solutions by running cold water over the walls of the test tube and, if necessary, induce crystallization by scratching the walls of the test tube with a stirring rod. Having determined that the concentration is such that crystallization is possible, reheat to dissolve the solid and allow to cool slowly. Record the following observations in a 5 x 4 matrix chart (previously prepared as part of the pre-lab preparation) for each possible pair of compound and solvent. 1. Solubility in hot and cold solvent. 2. Crystalline form - needles, plates, prisms, amorphous To conclude this section, make suggestions as to the solvents (or solvent pairs) you would recommend for the recrystallization of each compound....
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