Simple Distillation Flashcards
(23 cards)
How is vapor pressure created?
The molecules that make up a liquid are constantly moving, so the molecules on top escape.
Define boiling in terms vapor pressure.
When the vapor pressure is equal the pressure from the atmosphere
What is distillation?
Boiling a liquid and collecting the condensate in another vessel
What is a reflux?
Boiling of the liquid with return of the condensate to the original flask
Why is the thermometer so high in our flask?
If it were lowered into the solution, the impurities would affect the boiling point.
What kind of solvent do we need for a distillation? Why?
Soluble and nonvolatile, to raise the boiling point of the liquid but has no effect on vapor pressure
What if our solvent was insoluble and nonvolatile?
It would have no effect on boiling point or vapor pressure.
What must the boiling point difference be for a simple distillation to work?
40-50 degrees
What must the boiling point difference be for a fractional distillation to work?
About 1 degree
Define a theoretical plate.
Evaporation then condensation cycle to allow equilibrium to occur to make the lower boiling point compound more pure
The bottom of our graph is…
Pure cyclohexane
The top of our graph is…
Pure toluene
The middle, sloped region of our graph is…
an impure mixture
How does size effect boiling point?
The bigger the molecule, the higher the boiling point
How does branching effect boiling point?
Branched alkanes have lower boiling points than their unbranched counterparts
How does being cyclic effect boiling points?
Cyclic molecules have higher boiling points than their corresponding noncyclic molecules
How does hydrogen bonding effect boiling point?
Raises boiling point
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?
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.
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?
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.
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?
The effect of a soluble, nonvolatile liquid is to raise the boiling point. The vapor pressure will be slightly lower
What is the effect of an insoluble substance such as sand or charcoal? What is the temperature of the vapor above the boiling solution?
No effect
Why is it extremely dangerous to attempt to carry out a distillation in a completely closed apparatus?
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.
Why is better separation of two liquids achieved by slow rather than fast distillation?
