Distillation
What can distillation be used for?
1. Compound identification/Boiling point determination. 2. Compound purification.
How does it work? (3)
1. Heating a liquid mixture 2. Capturing the resultant hot vapors and then cooling them to obtain the pure liquid 3. Collecting the pure compounds (one at the time)
How many degrees does bp rise for each CH2 group?
27
What do ethanol and water form?
A minimum boiling azeotrope.
The ethanol-water azeotrope
A mixture of liquids of a certain definite composition that distills at a constant temperature without change in composition. 95% ethanol.
What should the process of fractional distillation be?
Adiabatic. Heat should be transferred from the ascending vapor to descending liquid with no net loss or gain of heat.
Why is a copper or steel sponge the best packing mechanism?
Easy to put into column Has a large surface area Good heat transfer characteristics.
Compounds at higher vp will boil at higher temperatures. T/f
False. Higher vp will boil at lower temp.
Smaller height, more or less plates?
More. More efficient.
Should you distill to dryness? why?
NO! Leave 2ml left over. High boiling explosive peroxides can become concentrated.
How filled should the flask be in distillation?
No more than 2/3.
Is boiling point a good indication of purity?
No.
Can fractional distillation be carried out on a microscale <1mg?
No. Only 4 ml.
What about a very large surface area? Desirable?
No. Will absorb much of the material being distilled.
What is Height equivalent to a theoretical plate (HETP)?
Other things being equal, the number of theoretical plates is proportional to the height of the column, so various packings are evaluated according to height equivalent to HETP.
During a simple distillation, the liquid is vaporized and condensed at different times or the same times?
Same time.
Where should the thermometer be positioned?
Slightly below the bottom part of the distilling head's lateral arm. Must not touch any glassware's wall.
What happens to the temp when first distillate starts collecting?
Temp should remain constant.
When is simple distillation used? (2)
The liquid has a non-volatile component. Solid.
When is simple distillation used? (3)
The liquid is contaminated by another liquid and their bp are at least 70C apart.
What is distillation?
The process of heating a liquid until it boils, capturing and cooling the resultant hot vapors, and collect the condensed vapors.
What is the boiling point?
The temp at which vp of liquid = external pressure (1atm).
Why are boiling chips added?
To promote even boiling.
What is the column packed with?
some material on which heat exchange between ascending vapor and descending liquid can take place.
How are boiling points determined during distillation?
By recording the temp.
How can distillation purify a compound?
By separating it from a non-volatile or less-volatile material.
What mixture did we use in the lab?
DCM and Toluene
What happens if the fractionating column is tilted?
Distillation is inefficient.
When is fractional distillation used?
When boiling points of two liquids are less than 70.
When is simple distillation used? (1)
When the liquid is relatively pure. <10% contaminates.
Do you grease all components?
Yes.
Is a large surface area desirable?
Yes.
What can packing material be?
glass beads glass helices copper or steel sponge.