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The Extraction of Benzoic Acid from a Mixture

The Extraction of Benzoic Acid from a Mixture -...

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Introduction The goal of the experiment The Extraction of Benzoic Acid from a Mixture is to remove, by extraction, benzoic acid from a mixture containing benzoic acid, methyl orange, and cellulose, as well as to determine a percent composition of benzoic acid, which was 51.14%. The goal of the experiment The Recrystallization of Benzoic Acid is to purify, by recrystallization, a sample of benzoic acid obtained from the prior experiment, as well as to determine a percent recovery of benzoic acid, which was . Theory, Reactions, and Mechanisms Extraction is the process of removing a desired substance from a mixture containing other substances. Two factors must be considered with an extraction: polarity and the partition coefficient. Extraction of one substance from another depends mainly upon differences in the polarities of the substances. Polar molecules are allowed to dissolve in each other as a result of the different polarities causing interactions between their polar molecules. It is important to remember during extraction that “like dissolves like”. This means that a polar molecule will dissolve more readily in a polar solvent then in a non-polar solvent, or that a non-polar molecule will dissolve more readily in a non-polar solvent then in a polar solvent. The partition coefficient is a ratio of the solubility of a compound, substance A, in an organic solvent compared to the solubility of the same compound in an aqueous layer. (See fig. 1) Figure 1. Partition Coefficient equation K d = [A]org [B] aq. In the experiment The Extraction of Benzoic Acid from a Mixture, a chemically active extraction is necessary in order to extract the benzoic acid from the mixture. A chemically active extraction changes the polarity of a substance through the initiation of a chemical reaction. Based solely on molecular
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structure, benzoic acid is considered a polar molecule. The COOH group causes the molecule to be slightly polar. Because of it being slightly polar it is able to dissolve in diethyl ether which is a non-polar solvent. The combination of a strong acid and strong base results in the formation of a salt and water according to the Acid/Base Theory. 1M NaOH is combined with the mixture containing benzoic acid and methyl orange. This results in the formation of sodium benzoate (the carboxylate salt form of benzoic acid) and water. The sodium benzoate and water, which are both polar molecules, are extracted from the non-polar ether mixture into a separate, aqueous layer. NaOH, which is a strong base, dissociates into Na + and OH - ions in aqueous solution. The OH - ions react with the hydrogen of the benzoic acid, forming H 2 0. This reaction permits the extraction of the benzoic acid from the mixture by changing the polarity of the benzoic acid. (See Fig. 3) Figure 3.
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