Simple Distillation

Distillation is a separation technique that takes advantage of what?

Takes advantage of the boiling point properties of mixtures.

How do you perform distillation?

A miscible mixture of two liquids with a significant difference in boiling points, at least 20C is heated.

The Process of vaporizing a liquid mixture in one vessel and condensing the vapors into another is what?

Distillation.

SImple Distillation involves what? What is it most useful for?

Only a single vaporization-condensation cycle.

It is most usual for purifying a liquid that contains either nonvolatile impurities or small amounts of higher or lower-boiling impurities.

What is the vapor pressure of a liquid? Explain by considering a closed container of a liquid.

Initially some of this liquid evaporates, but only until the rate of vaporization equals the rate of condensation. After this point is reached, there is no further change in the system, and the liquid and vapor are at equilibrium.

Once established, the pressure exerted by the vapor above the liquid is called vapor pressure.

Define Volatility. What does a more or less volatile liquid do?

The tendency for a liquid to vaporize.

• More volatile liquid has a higher vapor pressure.

• Less volatile liquid has a lower vapor pressure.

Define boiling.

A liquids evaporation process can be faster if heated. As the liquid is heated, the molecules within it will gain the energy to escape the liquid phase and transition into the gas phase in the form of bubbles—boiling.

Define boiling point. Is it the same as bubble point?

Boiling point is the temperature at which the vapor pressure of a liquid is the same as the atmospheric pressure.

Bubble point is the temperature at which the first bubbles start to form in a miscible solution that is being heated.

In pure liquids the bubble point is the boiling point.

If the gas phase is rich with molecules of the more volatile component, how will the vapor pressure and boiling point be?

More Volatile

Higher VP

Lower BP

If the gas phase is rich with molecules from the less volatile component, how will the vapor pressure and boiling point be?

Less volatile

Lower VP

Higher BP

In a mixture of miscible liquids, at which temperature does the solution boil?

The solution boils when the total vapor pressure of the solution equals the atmospheric pressure. Occurs at a temperature between the boiling points of the two pure liquids.

How does the composition of the distillate change over time during a distillation of a mixture of liquids?

As the distillation progresses, the temperature needed to boil the solution increases as the more volatile component boils off earlier.

Early—distillate is rich of the more volatile component.

Middle—distillate contains a mix of the two components.

End—distillate is rich of the less volatile component.

How is a vapor-liquid equilibrium diagram used to determine the composition of the liquid and vapor in a distillation?

Shows the change in both the composition of the liquid in the flask and the distillate over the course of the distillation.

Two curves:

• Bottom curve: the boiling point of the liquid in the flask as it related to its composition.

• Higher curve: temperature of the vapor as it relates to its composition, the distillates composition.

How do you determine the vapor pressure?

Know the vapor pressure of the pure substances and the mole fraction (molar contribution of each liquid to total mixture).

Raoult’s law: Pa = (Pa*)(Xa)

Pa = vapor pressure of liquid component in mixture

Pa* = vapor pressure of liquid pure

Xa = mole fraction of liquid component

Daltons Law of partial pressure: P= Pa + Pb…

How do you find the mole fraction?

Divide the number of moles of the liquid component over the total number of moles of each component in the liquid mixture.