Simple Distillation

Question 1

How is vapor pressure created?

Answer 1

The molecules that make up a liquid are constantly moving, so the molecules on top escape.

Question 2

Define boiling in terms vapor pressure.

Answer 2

When the vapor pressure is equal the pressure from the atmosphere

Question 3

What is distillation?

Answer 3

Boiling a liquid and collecting the condensate in another vessel

Question 4

What is a reflux?

Answer 4

Boiling of the liquid with return of the condensate to the original flask

Question 5

Why is the thermometer so high in our flask?

Answer 5

If it were lowered into the solution, the impurities would affect the boiling point.

Question 6

What kind of solvent do we need for a distillation? Why?

Answer 6

Soluble and nonvolatile, to raise the boiling point of the liquid but has no effect on vapor pressure

Question 7

What if our solvent was insoluble and nonvolatile?

Answer 7

It would have no effect on boiling point or vapor pressure.

Question 8

What must the boiling point difference be for a simple distillation to work?

Answer 8

40-50 degrees

Question 9

What must the boiling point difference be for a fractional distillation to work?

Answer 9

About 1 degree

Question 10

Define a theoretical plate.

Answer 10

Evaporation then condensation cycle to allow equilibrium to occur to make the lower boiling point compound more pure

Question 11

The bottom of our graph is…

Answer 11

Pure cyclohexane

Question 12

The top of our graph is…

Answer 12

Pure toluene

Question 13

The middle, sloped region of our graph is…

Answer 13

an impure mixture

Question 14

How does size effect boiling point?

Answer 14

The bigger the molecule, the higher the boiling point

Question 15

How does branching effect boiling point?

Answer 15

Branched alkanes have lower boiling points than their unbranched counterparts

Question 16

How does being cyclic effect boiling points?

Answer 16

Cyclic molecules have higher boiling points than their corresponding noncyclic molecules

Question 17

How does hydrogen bonding effect boiling point?

Answer 17

Raises boiling point

Question 18

In the simple distillation experiment, can you account for the boiling point of your product in terms of the known boiling points of the pure components of your mixture? If so, how? If not, why not?

Answer 18

There will not be much correlation. The distillation will begin at a temperature above the lower boiling component and end below the boiling point of the higher boiling component.

Question 19

From the plot of the boiling point versus the volume of distillate in the simple distillation experiment, what can you conclude about the purity of your product?

Answer 19

The conclusion should be that the distillate is not pure. No distinct line to know when one begins and one ends. Distillation of cyclohexane and toluene crossed over into the other’s range. Would need to perform more distillations to better purify the solvents.

Question 20

What is the effect on the boiling point of a solution produced by a soluble nonvolatile substance? What is the temperature of the vapor above the boiling solution?

Answer 20

The effect of a soluble, nonvolatile liquid is to raise the boiling point. The vapor pressure will be slightly lower

Question 21

What is the effect of an insoluble substance such as sand or charcoal? What is the temperature of the vapor above the boiling solution?

Answer 21

No effect

Question 22

Why is it extremely dangerous to attempt to carry out a distillation in a completely closed apparatus?

Answer 22

The closed system is not designed to withstand the pressure which may develop. If pressure inside the system exceeds the pressure that the glassware can handle, the apparatus can explode, which can be dangerous.

Question 23

Why is better separation of two liquids achieved by slow rather than fast distillation?