Acid-BaseExtractionLab - Chemistry 12A Foothill College...

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Chemistry 12A Foothill College Acid-Base Extraction of a Mixture of Organic Compounds Abstract In this lab, we will be separating a three-component organic mixture by acid-base extraction. Extraction is the most efficient method for separating organic compounds with differing solubilities in water. Background Acid-base extraction is a sub-category of liquid-liquid extractions in which the water layer is made acidic or basic in order to cause proton transfer. Most organics are only soluble in polar organic solvents like dichloromethane or diethyl ether, while very small organics ( six carbons) or very polar organics (like organic salts) are soluble in water. If a mixture contains, say, an organic salt (like sodium benzoate NaC 7 H 5 O 2 ) and a neutral organic like naphthalene (C 10 H 8 ), the two can be easily separated by adding water until the sodium benzoate is dissolved, leaving the naphthalene behind. In order to be sure that we don't add so much water that even the naphthalene dissolves (given enough solvent anything will dissolve), we would first dissolve both components of the mixture in an organic solvent, then we would add a small portion of water to allow the ionic salt to dissolve while allowing the napthalene to stay behind in the organic layer. Consider the solubility chart below. Why is it that benzoic acid dissolves in base but not in water? The answer is that the base (though mostly water) contains solvated hydroxide ions which will instantly deprotonate benzoic acid on contact, thereby creating ionic sodium benzoate. The benzoate ion dissolves into the aqueous layer because it has become a salt and is now soluble in water. Solubility
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This note was uploaded on 10/19/2010 for the course CHEMISTRY chem12 taught by Professor Vtam during the Spring '09 term at Foothill College.

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Acid-BaseExtractionLab - Chemistry 12A Foothill College...

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