At the maximum or minimum boiling point eutectic the

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Unformatted text preview: ents (positive deviation) or at temperatures greater than either of the pure components (negative deviation). 2. At the maximum or minimum boiling point (eutectic), the liquid and vapor have the same composition. Distillation of immiscible liquids: In a system consisting of two liquids that are almost completely immiscible, the two components separate into mutually exclusive layers. In other words, within each layer, the mole fraction of that component is almost 1. Then, we may write P = PA* + PB*. (6.20) If nA and nB are the compositions of each component in the vapor, we get nA P A (6.21) nB = P B In other words, the vapor contains more of the more volatile component, as we would normally expect. Since the molar masses are constants, this immediately gives rise to a useful relationship between the masses of the two substances in the vapor: wA P MA A wB = P MB . B Example 6.4, Problems 6.12–6.14. Steam distillation is a very useful technique based on these principles for the extraction of organic compounds that are immiscible with water. Since the total vapor pressure of the system is the sum of the two vapor pressures, the liquid mixture boils at temperatures far lower than the boiling points of either liquid. Therefore, it is possible to extract organic compounds that may decompose or undergo reactions if heated to their boiling points. Reading Assignment: Distillation of partially miscible liquids (p. 246). Other topics covered: Partially miscible liquids Solid-liquid systems Three-component systems....
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This document was uploaded on 02/28/2014 for the course CHEM 311 at LA Tech.

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