Why do different fractions form from fractional distillation?

In summary, the fractions obtained from fractional distillation can have overlapping carbon chain lengths despite having distinct boiling temperatures due to variations in the structure of the chains. This can be demonstrated through calculations of liquid and vapor compositions at equilibrium for different temperatures. Chemical calculators, such as BATE, can aid in these calculations for laboratory and educational purposes.
  • #1
Cheman
235
1
Fractions of distillation...

Some of the fractions which result from fractional distillation seem to share carbons of the same length - yet these form different fractions. Why?

Eg - Petrol is carbon chain length 4 - 12, naptha is 7 - 14 and kerosine is 11 -15; why the overlap when they boil at very distinct temps. ie - petrol 40 - 100, naptha is 100 - 150 and kerosine is 150 - 250 degrees C.

Thanks. :smile:
 
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  • #2
Cheman said:
Some of the fractions which result from fractional distillation seem to share carbons of the same length - yet these form different fractions. Why?

Eg - Petrol is carbon chain length 4 - 12, naptha is 7 - 14 and kerosine is 11 -15; why the overlap when they boil at very distinct temps. ie - petrol 40 - 100, naptha is 100 - 150 and kerosine is 150 - 250 degrees C.

The simplest answer will be that boiling point depends not only on number of carbons, but also on the chain structure - whether it is straight or branched.


Chemical calculators for labs and education
BATE - pH calculations, titration curves, hydrolisis
 
  • #3
"Distillation" --- evaporation of a MIXTURE. Do a few calculations of liquid and vapor compositions that are at equilibrium at the temperatures bounding the fractions you've listed.
 

1. What is fractional distillation?

Fractional distillation is a process used to separate a mixture of liquids with different boiling points. It involves heating the mixture and collecting the vapors as they condense at different temperatures, resulting in the separation of the liquids.

2. What are the key components used in fractional distillation?

The key components used in fractional distillation include a distillation column, a condenser, a heat source, and a collection vessel. The distillation column is where the separation of the liquids occurs, while the condenser cools and condenses the vapors. The heat source provides the energy needed to vaporize the liquids, and the collection vessel collects the separated liquids.

3. How does fractional distillation work?

Fractional distillation works by taking advantage of the differences in boiling points of the liquids in a mixture. The mixture is heated, and as the temperature rises, the liquid with the lowest boiling point will vaporize first. The vapors then rise up the distillation column, where they are cooled and condensed. The condensed liquid is collected in the collection vessel, while the remaining vapors continue to rise and condense until all the liquids have been separated.

4. What are the applications of fractional distillation?

Fractional distillation is commonly used in the petroleum industry to separate crude oil into different fractions, such as gasoline, diesel, and kerosene. It is also used in the production of alcoholic beverages and essential oils, as well as in laboratory settings to purify chemicals and separate mixtures.

5. How is fractional distillation different from simple distillation?

The main difference between fractional distillation and simple distillation is the presence of a distillation column. In simple distillation, the mixture is heated and the vapors are directly condensed, resulting in less effective separation of liquids with similar boiling points. Fractional distillation, on the other hand, utilizes the distillation column to create multiple vapor-liquid equilibrium stages, allowing for more precise separation of liquids with similar boiling points.

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