Krystel Iris M. de Castro 20B Experiment 1: Purificaon of Benzoic Acid January 30, 2017 Objectives: To remove impurities from crude benzoic acid by recrystallization To determine the percent recovery of benzoic acid from recrystallization To determine the melng point of recrystallized benzoic acid and test for its purity Introduction: A method commonly used in purifying solids is recrystallization, which employs the solubility properties of compounds (1). The sample is first dissolved in a hot solvent. Then, the solution is cooled before adding decolorizing charcoal to prevent the loss of products due to frothing (2). Gravity filtration removes insoluble impurities, including the decolorizing charcoal which adsorbs colored impurities (2). However, premature crystallization may occur because the solution cools as it runs through the filter. The following measures can be taken to diminish its possibility: using warm glassware, using a short-stemmed or stemless glass funnel, using fluted filter paper to minimize contact with the walls of the funnel, and filtering only a lile of the soluon at a me to reduce cooling (2, 3). Meanwhile, the soluble impurities remain in the supernatant solution to be disposed in suction filtration, wherein the crystals are harvested (1). These crystals are formed by slow cooling, allowing the solution previously filtered to cool down to room temperature. Placing the solution in an ice-water bath to hasten the crystallization process only traps impurities within the lattice (2). During cooling, the solution should be covered with a watch glass or beaker to protect it from airborne contaminants. Cold water should also be poured over the crystals during sucon filtraon to wash off the soluon and inhibit the deposion of the soluble impuries on the crystals (2). The percent recovery is calculated and the melting point of the recrystallized compound is determined to test for its purity. Reagents: Reagent Description Safety Precautions Benzoic Acid Physical State: Solid Boiling Point: 249.2°C (480.6°F) Melting Point: 122.4°C (252.3°F) Molecular Weight: 122.12g/mol Solubility: Very slightly soluble in cold water. Skin and eye irritant Decolorizing Charcoal Physical State: Solid Flammable