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Questions and Answers
What happens during the distillation of a binary mixture with positive deviation?
What happens during the distillation of a binary mixture with positive deviation?
What is a characteristic feature of negative deviation in distillation?
What is a characteristic feature of negative deviation in distillation?
In steam distillation, under what condition does the distillation occur?
In steam distillation, under what condition does the distillation occur?
How does the presence of a non-volatile solute affect the vapor pressure of a solvent?
How does the presence of a non-volatile solute affect the vapor pressure of a solvent?
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Why is the composition of an azeotropic mixture considered constant?
Why is the composition of an azeotropic mixture considered constant?
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Which example illustrates a negative deviation azeotrope?
Which example illustrates a negative deviation azeotrope?
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What principle does steam distillation leverage for distilling immiscible liquids?
What principle does steam distillation leverage for distilling immiscible liquids?
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Which factor contributes to the vapor pressure being lower when a solute is added to a solvent?
Which factor contributes to the vapor pressure being lower when a solute is added to a solvent?
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In relation to distillation, what property is important when separating volatile oils from plants?
In relation to distillation, what property is important when separating volatile oils from plants?
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What is a fundamental characteristic of a low boiling point azeotrope?
What is a fundamental characteristic of a low boiling point azeotrope?
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Study Notes
Distillation of Binary Mixtures
- The relationship between vapor pressure and the composition of binary liquid phases forms the core principle of distillation.
- Liquids with higher vapor pressures are more volatile and boil at lower temperatures.
- When a mixture of two substances with different volatilities is distilled, the composition of the vapor phase in equilibrium with the liquid phase will be different from the composition of the liquid phase.
- The composition of the condensate (distillate) will be closer to the composition of the vapor phase.
Positive Deviation from Raoult's Law
- Distillation results in an azeotropic mixture, which is a mixture of constant composition with a constant boiling point.
- The azeotropic mixture is composed of the more volatile constituent (higher vapor pressure) and a mixture of constant composition.
- The boiling point of the azeotropic mixture is lower than the boiling points of the individual components.
- Examples of positive deviations from Raoult's Law include ethanol + water and methanol + benzene.
Negative Deviation from Raoult's Law
- Distillation results in an azeotropic mixture with a higher boiling point (lower vapor pressure) than the individual components.
- Examples of negative deviations from Raoult's Law include water + acetic acid and chloroform + acetone.
Distillation of HCl + H2O Azeotrope
- The HCl + H2O azeotrope has a composition of 20.22% HCl and a boiling point of 108.08 °C.
- This azeotrope is a high boiling (low vapor pressure) azeotrope.
- The constant composition and reproducibility of this azeotrope make the 20.22% HCl solution a standard solution in analytical chemistry.
Distillation of Immiscible Liquids
- When a mixture of two immiscible liquids is heated, distillation can occur when the sum of the partial pressures of the two liquids exceeds atmospheric pressure.
- This principle is utilized in steam distillation, which is used to isolate volatile organic compounds that are insoluble in water.
- Steam distillation occurs at a temperature lower than the normal boiling point of the solute, preventing decomposition of sensitive compounds.
- Bromobenzene, for instance, boils at 95 °C in steam distillation, while its normal boiling point is 156.2 °C.
Colligative Properties
- When a non-volatile solute is added to a volatile solvent, the vapor pressure of the solvent is lowered due to the solute reducing the escaping tendency of the solvent.
- This phenomenon is described by Raoult's Law.
Summary of Colligative Properties
- Lowering of vapor pressure
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Description
Test your understanding of the principles of distillation and the relationship between vapor pressure and composition in binary mixtures. This quiz covers key concepts such as vapor pressures, the composition of distillates, and positive deviations from Raoult's Law. Dive into the world of azeotropic mixtures and their implications in distillation processes.
