Experiment 3: Distillation

When will simple distillation do a reasonable job of separating a mixture?

1) When the difference on boiling points is over 100° 2) When one of the components will not distill because of a lack of volatility 3) Is the impurity is present on a very small amount and is less volatile than the desired compound

The distillation process

A liquid is heated to its boiling point, the vapors expand out of the container and are then cooled below the boiling point where they recondense as a liquid

Azeotrope

A mixture with a fixed composition that cannot be altered by either simple or fractional distillation. Mixture of two liquids of a certain composition that behaves as a pure compound. Distills from beginning to end at a constant temperature, giving a distillate of constant azeotropic composition.

Raoult's Law

A solution which follows Raoult's Law is ideal. The total pressure of the solution is equal to the sum of the partial pressures of each liquid. The partial pressures are dependent upon the vapor pressure of the pure liquid and its mole fraction in the solution.

What happens during distillation?

During distillation, a liquid mixture is boiled at a certain temperature and a component of the mixture is vaporized and collected. One or more components can be separated from other components and then cooled and condensed.

Difference between fractional distillation apparatus and simple distillation apparatus

Fractional distillation requires the insertion of a fractionating column between the distilling flask and the distillation head. The fractionating column is filled with a packing material.

Methanol and water azeotrope

Methanol and water do not form an azeotrope

Our distillation procedure

Provided with a mixture of methanol and water but not the % composition of the mixture. This is to be determined after distillation is completed.

Simple Distillation

Purification of a liquid which contains nonvolatile impurities. Separation of a mixture of liquids where the difference of the two boiling points is very large (about 100°C or more).

Simple distillation - Rate of Heating

Rate of heating should be adjusted to the proper rate at which distillate leaves the condenser. At a rate greater than 1-3 drops per second, equilibrium is not established within the distillation apparatus, and the separation may be poor.

Why is separation by distillation possible?

Separation by distillation is possible because the various ingredients of the mixture have different boiling points.

Fractional Distillation

Separation of a mixture of liquids where the difference of the two boiling points is much closer.

What is the boiling point of a liquid that is open to the atmosphere?

The boiling point is the temperature at which the internal vapor pressure of the liquid becomes equal to the atmospheric pressure (760 mmHG)

What does the process of distillation rely on?

The process of distillation relies on the fact that the different components of a mixture will boil and therefore vaporize at different temperatures

Distillate

The resultant liquid of a distillation procedure

The Boiling Point

The temperature at which the internal vapor pressure of the liquid is equal to the pressure exerted by its surroundings

What happens to the temperature throughout the boiling process of a pure liquid?

The temperature remains constant. At the boiling point, the liquid and the vapor are in equilibrium. If the composition of each phase remains constant, the temperature will remain constant.

What makes azeotropes different from other mixtures?

Their ability to keep their compositions constant during distillation. This means that the vapor pressure of the azeotropic mixture has the same ratio of components as the original mixture

Simple Distillation - Distillation Theory

There are three types of temperature behavior during simple distillation A) Single pure component B) Two components of similar boiling points C) Two components with widely different boiling points

Ideal Mixture

Two liquid mixture which follows Raoult's Law and does not form an azeotrope

Non-Ideal Mixture

Two liquid mixture which forms an azeotrope.

Ethanol/toluene azeotrope

boiling point: 77 degrees, composition is 32% toluene by weight.

Ethanol/Water azeotrope

boiling point: 78 degrees, composition is 95.5% ethanol by weight

What is distillation?

- Can be used as a method for purifying a single liquid - Can be used a means of separating a liquid from a dissolved solid or from a mixture of miscible liquids - Liquid or mixture is heated and when it boils, the vapors are condensed into a separate receiver.

Distillation Process

- When a mixture of A and B of specific composition is heated, the total vapor pressure of the liquid will rise until it is equal to the external vapor pressure. - The mixture will begin to boil - The vapor which first forms is enriched in the more volatile component

Vapor Enrichment

When a mixture of two miscible liquids with different boiling points is heated, the vapor will have a different composition than the liquid. The vapor is enriched in the more volatile component (lower bp)

Separation of a Mixture

When a solution of two miscible liquids is distilled, boiling will begin when the total pressure of the solution os equal to the atmospheric pressure.