Distillation miscible liquids

Distillation miscible liquids - CHEM 2423 Distillation of a...

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CHEM 2423 Distillation of a Mixture Dr. Pahlavan 1 EXPERIMENT 7 - Distillation – Separation of a Mixture Purpose: a) To purify a compound by separating it from a non-volatile or less-volatile material. b) To separate a mixture of two miscible liquids (liquids that mix in all proportions) with different boiling points. Equipment / Materials: large test tubes(3) test tube rack (1) 10-mL graduated cylinder 50- mL round bottom flask clamp (1 or 2) heating mantle condenser (1 or 2) thermometer ringstand glass adaptor grease rubber tubing (2) boiling chips thermometer adaptor 50- mL round bottom flask unknowns ( A and B) Discussion: Distillation is one of the oldest and still most common methods for both the purification and the identification of organic liquids. It is a physical process used to separate chemicals from a mixture by the difference in how easily they vaporize. As the mixture is heated, the temperature rises until it reaches the temperature of the lowest boiling substance in the mixture, while the other components of the mixture remain in their original phase in the mixture. The resultant hot vapor passes into a condenser and is converted to the liquid, which is then collected in a receiver flask. The other components of the mixture remain in their original phase until the most volatile substance has all boiled off. Only then does the temperature of the gas phase rises again until it reaches the boiling point of a second component in the mixture, and so on. The boiling point of a substance—determined by distillation—is a useful physical property for the characterization of pure compounds. At any given temperature a liquid is in equilibrium with its vapor. This equilibrium is described by the vapor pressure of the liquid. The vapor pressure is the pressure that the molecules at the surface of the liquid exert against the external pressure, which is usually the atmospheric pressure. The vapor pressure is a very sensitive function of temperature. It does not increase linearly but in fact increases exponentially with temperature. The vapor pressure of a substance roughly doubles for every increase in 10 °C, Figure 1. When the vapor pressure of the liquid equals the applied pressure, the liquid boils. Thus, the boiling point of a liquid is the temperature at which the vapor pressure equals the applied pressure. The normal boiling point of a liquid is the temperature at which the vapor pressure of a liquid equals atmospheric pressure (1 atm). The boiling point of a liquid is a measure of its volatility.
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CHEM 2423 Distillation of a Mixture Dr. Pahlavan 2 Fig 1. Vapor pressure dependence on temperature for water The successful application of distillation techniques depends on several factors. These include the difference in vapor pressure (related to the difference in the boiling points) of the components present, the size of the sample, and the distillation apparatus. Distillation relies on the fact that the vapor above a liquid mixture is richer in the
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Distillation miscible liquids - CHEM 2423 Distillation of a...

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