PHARCAL Laboratory Module 15: Distillation

The _____________ of a substance is a measure of its tendency to change into gaseous or vapor state.

vapor pressure

The _________ the vapor pressure of a substance is, the more this tends to be in the vapor state.

higher

Substances whose molecules are held together by weak intermolecular attractive forces exhibit this characteristic. These can also be considered as _____________.

volatile substances

The vapor pressure of a substance is _____________ related to its boiling point.

INVERSELY

The _____________ of a liquid is the temperature at which the vapor pressure equals atmospheric pressure.

boiling point

_____ thermal energy is needed for a substance with high vapor pressure to reach the atmospheric pressure

LESS

At this temperature, ___________ can overcome the attractive forces between the molecules of the liquid resulting in vapors seen to form bubbles which rise rapidly through the liquid and escape through the gaseous state. 

thermal agitation

Application of heat ____________ the kinetic energy of particles in the liquid state. This kinetic energy of particles results in their escape from the liquid state to the gaseous (vapor) state; thereby, ____________ the vapor pressure.

INCREASES
INCREASING

Vapor pressure lowering translates into boiling point _____________

elevation

Both vapor pressure lowering and boiling point elevation are __________________ of solutions.

colligative properties

Boiling point is ___________ for identical molecules. This is the phenomenon that is the basis for the method of purification of organic compounds known as _____________.

CONSTANT
distillation

_____________ is the process of vaporizing a substance, condensing the vapor, and collecting the condensate in another container. This technique is useful for separating a mixture when the components have ___________ boiling points. It is the principal method of purifying a liquid.

Distillation
different

What are the 4 types of distillation?

1. -

2. -

3. -

4. -

Simple distillation
Vacuum distillation
Fractional distillation
Steam distillation

In ________________ , a large temperature difference between boiling points of the components to be purified is required to obtain an efficient separation. This makes the technique of simple distillation inefficient for the separation of components having a temperature difference between boiling points of 30⁰ to 50⁰C.

Simple distillation

Usually, grossly _________ materials result from simple distillation. Ins spite of this limitation, simple distillation is considered as a means of purification if carried out slowly enough so that __________ of the vapor is avoided.

impure
superheating

___________ leads to decreased efficiency of separation and to erroneous temperature readings.

superheating

Superheating also results in irregular ebullition or _________. This irregular ebullition can be prevented if a few chips of _______ (porcelain chips or commercial microporous boiling chips) or __________ are added to the reaction system in the flask.

bumping
porous plate
capillary tubes

For LOW boiling liquids, superheating is prevented by heating the system in a ____________.

water bath

Distillation under reduced pressure or _______________  is employed in the purification of organic compounds which partially or completely decompose before their normal boiling points are reached. This type of distillation is carried out at a temperature lower than the normal boiling point as a result of the reduction of pressure in the system.

vacuum distillation

When the external pressure is decreased, the boiling point is considerably _________, and the distillation may usually be conducted without danger of decomposition of the components.

reduced

If more than one fraction is collected, this vacuum distillation can be combined with __________ distillation.

FRACTIONAL

The ______________ (Rotavap) is an equipment that is commonly used in the laboratory. This is used in the concentration of plant extracts in volatile solvents such as ethanol and ethyl acetate, both of which do not easily evaporate at room temperature and atmospheric pressure.

Rotary evaporator

The _____________ is "recovered" or collected in the receiver, so it can be reused in subsequent extractions.

evaporated solvent

In ______________, successive distillations are carried out in an automatic way without collecting or transferring the immediate fractions.

fractional distillation

What are the 4 types of fractionating columns?

1. -

2. -

3. -

4. -

Hempel column
Vigreux column
Bubble-cap column
modified Hempel column

_______________ is a simple glass tube filled to within a few cm of the side arm with a suitable packing.

Hempel column

_____________ have indentations inclined at 45 degrees

Vigreux column

During fractional distillation, vapors of the material being distilled are ___________ to come in contact with liquid of changing composition as it passes through the fractionating column.

ALLOWED

In ____________, the organic compound purified co-distills with water. This is effected by passing steam through a hot mixture of the compound and water. If a mixture of two immiscible liquids is distilled, the boiling point will be the temperature at which the sum of the individual vapor pressures is equal to that of the atmosphere.

steam distillation

The steam distillation follows __________________

Dalton’s law of partial pressures

___________________ states that “When two or more gases or vapors which do not react chemically with one another are mixed at constant temperature, the sum of their individual vapor pressures is equal to the total pressure exerted by the system.”

Dalton’s law of partial pressures

The boiling point of the mixture to be steam distilled will be ________ than the boiling point of even the more volatile component. Since of the components is water, steam distillation at atmospheric pressure will result in the separation of the higher boiling point component at a temperature below ____⁰C.

LOWER
100

The number of molecules of each component in the vapor will be _____________ to the vapor pressure of the pure liquid at that temperature.

PROPORTIONAL

The weights of the two liquids collected in the reservoir are __________________ to their vapor pressures and their molecular weights. This relationship, however, does not apply to water-soluble compounds that are steam distilled because other factors such as hydrogen bonding and solvation have to be considered. These factors often _________ the relationship based on vapor pressures.

DIRECTLY PROPORTIONAL
invert

1. Prepare a  _____________  set-up. Use the illustration of the set up in Figure 15.3 as a guide. Have it approved before any attempt to use it.

simple distillation

2. Add 50 mL of ____________ to 25 mL of ___________________ USP. Mix thoroughly.

distilled water
Aromatic ammonia spirit

3. Render the solution slightly acidic to litmus by adding ________________.

diluted sulfuric acid

4. Transfer to the distilling flask, place ___________ , and distill using a hot water bath.

boiling chips

5. Note the __________ at which the first drops distill over. Discard the first volumes of distillate.

temperature

6. Continue the distillation until a steady stream of ________ is observed. Collect the ______ and record the _________.

bubbles
distillate
temperature

7. Observe the _____ of the distillate.

odor

8. To a small portion of the distillate, place a few drops of _____________ and a few drops of _______________. Heat on a warm water bath for about 30 minutes and observe the color of the solution.

potassium dichromate TS
concentrated sulfuric acid

Clean-up: If the sample of distillate turns green (or blue) after heating with potassium dichromate TS and sulfuric acid, collect the remaining distillates in a reagent bottle labeled “_________________”. If the test solution does not turn green (or blue), add sufficient quantity of _____________ and continue heating until it turns green (or blue). Cool and neutralize with __________________ afterwards and dispose in the _____  with copious amount of water. Dispose the solution in the distilling flask in the sink with copious amount of water.

Recovered ethanol
95% ethanol
10% sodium bicarbonate
sink