Extraction Lab

Extraction Lab - Separating Acids and Neutral Compounds by Solvent Extraction PURPOSE OF THE EXPERIMENT Use solvent extraction techniques to

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Separating Acids and Neutral Compounds by Solvent Extraction PURPOSE OF THE EXPERIMENT Use solvent extraction techniques to separate a mixture consisting of a carboxylic acid and a neutral compound. BACKGROUND REQUIRED You should be familiar with the experimental techniques used to determine melting points, to test for acidity using pH paper, and to separate a solid from a solution using vacuum filtration. BACKGROUND INFORMATION Frequently, organic chemists must separate an organic compound from a mixture of compounds, often derived from natural sources or as products of synthetic reactions. One technique used to separate the mixture compounds is called extraction. Extraction is a process that selectively dissolves one or more of the mixture compounds into an appropriate solvent. The solution of these dissolved compounds is often referred to as the extract. Extraction processes include removal of soluble compounds from a solid matrix, such as occurs in brewing coffee or tea, or in decaffeinating coffee with liquid carbon dioxide. In the organic chemistry laboratory, however, extraction almost always refers to the transfer of compounds from one liquid solvent to another liquid solvent. A compound can be separated from impurities in a solution by extracting the compound from the original or first solvent into a second solvent. The compound must be more soluble in the second solvent than in the first solvent, and the impurities must be insoluble in the second solvent.
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Also, to effect the extraction, the two solvents selected must be immiscible, or not soluble in one another, so that they produce two separate solvent layers. After dissolving the mixture in the first solvent, the solution is added to the second solvent. The two layers are vigorously mixed to maximize the surface area between them. This mixing facilitates the transfer of a dissolved compound from one layer to another. Once the transfer process is complete, the layers are again allowed to form, as shown in Figure 1. Separation of the two layers then completes the separation of the desired compound from the impurities. Washing is the reverse process, in which the impurities are removed to the second solvent, leaving the desired compound in the original solvent, as shown in Figure 2. The amount of compound to be extracted determines whether macroscale or microscale techniques should be employed for the extraction. The chemical principles associated with the extractions are identical, but the techniques are somewhat different. Extractions using larger quantities of solvents, tens or hundreds of milliliters, require a separatory funnel, as shown in Figure 3. The solvent layers are mixed by shaking the separatory funnel. Then the layers are allowed to reform. The bottom layer is drained through the stopcock; the top layer is poured from the top of the separatory funnel. Microscale extractions can be conducted using a test
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This note was uploaded on 11/14/2010 for the course CHEM CHEM266L taught by Professor Christine during the Fall '10 term at Waterloo.

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Extraction Lab - Separating Acids and Neutral Compounds by Solvent Extraction PURPOSE OF THE EXPERIMENT Use solvent extraction techniques to

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