The Unknown Carboxylic Acid

The unknown carboxylic acid’s melting point was 108°C according to the Mel-Temp machine. The melting point is the temperature at which a solid precipitate changes into its liquid form upon heating. The melting point of benzoic acid, the aromatic carboxylic acid was 122°C. Thus, the product contained impurities which caused the solid to melt at a lower temperature than the actual temperature. Pure solids typically melt at higher temperatures while impure solids melt at lower temperatures. This is due to the fact that a solid cannot form when it is held together by tight intramolecular forces in its pure state. In its impure form, the intramolecular forces are weaker since the impurities prevent the tight packing of a solid. The melting point
The washing process may have not been successfully completed; either the substance was not washed enough or some of the precipitate washed away with the solvent. By performing a series of calculations, the molecular weight of the unknown was determined. The unknown carboxylic acid was titrated with 0.1 M NaOH. The solid was synthesized from the Grignard reaction. Deionized water and ethanol were both used to dissolve the solid. Then 2-3 drops of phenolphthalein were added to the Erlenmeyer flask as the indicator. Under acidic conditions from the unknown carboxylic acid, the indicator did not change colors. The titrant, NaOH, which is a strong base was added to the solution dropwise until the solution remained a light pink color. When the solution turned pink, this indicated that the acidic environment had become neutralized which is also known as the equivalence point. The volume of the amount of titrant, NaOH, that was added to neutralize the carboxylic acid was later used to calculate the molar weight of the unknown carboxylic acid. The volume of 0.1 M NaOH needed to titrate the carboxylic acid, was 20 mL. This value
Based on the molecular weight calculated which was 151 g/mole and the melting point of 108°C obtained from the experiment, the identity of the product was 4-ethylbenzoic acid. When comparing this to the correct identity of benzoic acid, its molecular weight was 122 g/mole and its melting point was 122°C. Therefore, there were errors that occurred within the experiment. One source of error was from the separation process. Some of the aqueous solution in the separatory funnel containing the ether could have potentially been drained off with the product and the NaOH. This would have caused some ether to remain in the final product which would cause a larger molecular weight to occur and the product would have a lower melting point. Another source of error could have been having leftover impurities that remained in the final precipitate after the completion of the filtering process. The washing process may have not been successfully completed; either the substance was not washed enough or some of the precipitate washed away with the solvent. This would have caused a lower melting point. Overall, the unknown carboxylic acid was experimentally determined to be 4-ethylbenzoic acid which was incorrect, and the unknown carboxylic acid product was supposed to be benzoic