Recrystallization of Benzoic Acid through Purification
OBJECTIVE: This experiment was performed to gain an understanding of the process of purification through the technique of recrystallization, compounding upon previously developed skills in determination of melting points and the process of thin layer chromatography.
EXPERIMENTAL: A thin layer chromatography (TLC) comparative trial was setup and executed, using both pure and impure samples of benzoic acid. A 50% EtOAc / 50% hexane mixture was utilized as the solvent. Using dichloromethane, the benzoic acid samples were mixed and spotted onto the TLC plate. After completion of the TLC trial, an ultraviolet (UV) light was utilized to visualize the staining of the plate. The TLC plate was …show more content…
The filter paper placed on the porous plate of the funnel was primed with water prior to connection of a vacuum hose, after which the crystallized solution was slowly poured into the funnel, ensuring not to overfill beyond the funnel’s capacity. After all solution was poured, the resulting moist crystals were scraped from the funnel filter paper onto dry filter paper to be pressed and dried prior to weighing of the recovered crystals to determine the percent recovery of the benzoic acid. A TLC trial was run on the purified benzoic acid, determining the recrystallized purity of the sample. As outlined in the initial TLC trial, the results were visualized under UV light and using iodine, then recorded. Finally, a melting point trial was conducted on the pure, dry benzoic acid, utilizing both fast and slow ramps, and the resulting melting point range was recorded to be 116.4° C – 123.1° …show more content…
Results of the melting point range obtained for impure benzoic acid (99.7° C – 118.1° C) were more broadened and depressed than that which were obtained and compared with a known value of pure benzoic acid, that being 122.35° C, as published by the CRC Handbook of Chemistry and Physics . After the process of recrystallization, the obtained purified sample melting point range was determined to be 116.4° C – 123.1° C which proves consistent with the aforementioned published value of the melting point of pure benzoic acid. The tested TLC trial plate yielded UV visibility and iodine staining for the impure sample, while the pure sample was only visible by UV light. This was attributed to iodine’s affinity for unsaturated and aromatic compounds. Given that the sample is an aromatic carboxylic acid, it was anticipated that the impurities found within it would react with iodine to yield visible staining. While the exact Rf values were not measure (or required to be measured), visual observation confirmed the pure sample would yield a higher Rf value based on spot travel
OBJECTIVE: This experiment was performed to gain an understanding of the process of purification through the technique of recrystallization, compounding upon previously developed skills in determination of melting points and the process of thin layer chromatography.
EXPERIMENTAL: A thin layer chromatography (TLC) comparative trial was setup and executed, using both pure and impure samples of benzoic acid. A 50% EtOAc / 50% hexane mixture was utilized as the solvent. Using dichloromethane, the benzoic acid samples were mixed and spotted onto the TLC plate. After completion of the TLC trial, an ultraviolet (UV) light was utilized to visualize the staining of the plate. The TLC plate was …show more content…
The filter paper placed on the porous plate of the funnel was primed with water prior to connection of a vacuum hose, after which the crystallized solution was slowly poured into the funnel, ensuring not to overfill beyond the funnel’s capacity. After all solution was poured, the resulting moist crystals were scraped from the funnel filter paper onto dry filter paper to be pressed and dried prior to weighing of the recovered crystals to determine the percent recovery of the benzoic acid. A TLC trial was run on the purified benzoic acid, determining the recrystallized purity of the sample. As outlined in the initial TLC trial, the results were visualized under UV light and using iodine, then recorded. Finally, a melting point trial was conducted on the pure, dry benzoic acid, utilizing both fast and slow ramps, and the resulting melting point range was recorded to be 116.4° C – 123.1° …show more content…
Results of the melting point range obtained for impure benzoic acid (99.7° C – 118.1° C) were more broadened and depressed than that which were obtained and compared with a known value of pure benzoic acid, that being 122.35° C, as published by the CRC Handbook of Chemistry and Physics . After the process of recrystallization, the obtained purified sample melting point range was determined to be 116.4° C – 123.1° C which proves consistent with the aforementioned published value of the melting point of pure benzoic acid. The tested TLC trial plate yielded UV visibility and iodine staining for the impure sample, while the pure sample was only visible by UV light. This was attributed to iodine’s affinity for unsaturated and aromatic compounds. Given that the sample is an aromatic carboxylic acid, it was anticipated that the impurities found within it would react with iodine to yield visible staining. While the exact Rf values were not measure (or required to be measured), visual observation confirmed the pure sample would yield a higher Rf value based on spot travel