NOTES: A.2 – Separation by Distillation. *Substances can often be separated by taking advantage of...
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Transcript of NOTES: A.2 – Separation by Distillation. *Substances can often be separated by taking advantage of...
![Page 1: NOTES: A.2 – Separation by Distillation. *Substances can often be separated by taking advantage of their different physical properties… remember the “Foul.](https://reader035.fdocuments.us/reader035/viewer/2022062722/56649f285503460f94c40456/html5/thumbnails/1.jpg)
NOTES: A.2 – Separation by
Distillation
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*Substances can often be separated by taking advantage of their different physical properties… remember the “Foul Water Lab”?
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Different liquids may be separated by:
> DENSITY – less dense
liquids will float on
top (oil on top of water)
**this only works if the 2
substances are insoluble in
each other
> BOILING POINT**
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**the boiling point of a liquid is the temperature at which the liquid boils or VAPORIZES (becomes a gas)
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● the separation of
liquid substances
according to their
differing boiling
points is called
DISTILLATION.
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DISTILLATION:
● a liquid mixture is heated
● the substance with the LOWER boiling point will vaporize first and leave the distillation flask
● it is then passed through a condenser where it is converted back to a liquid
● eventually, the second substance begins to boil
● each condensed liquid is called a DISTILLATE and can be collected separately
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Distillation Example:
Possible Components of a Distillation Mixture
Substance Formula Boiling Point (°C)
2-propanol
(rub. alcohol)
C3H7OH 82.4°C
Acetone C3H6O 56.5°C
Water H2O 100°C
Cyclohexane C6H12 80.7°C
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If were given a mixture containing the 4 liquids shown in the table above, in what order would you collect them using a distillation apparatus?
, , ,
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If were given a mixture containing the 4 liquids shown in the table above, in what order would you collect them using a distillation apparatus?
acetone, cyclohexane, 2-propanol, water
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NOTES: A.3 – Petroleum Refining
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**the techniques of distillation are used in the refining of petroleum, however, crude oil is a complex mixture of many compounds, so the techniques must be applied in a large-scale oil refinery.
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● instead of separating crude oil into pure substances (single distillates), the refining process produces several mixtures, called FRACTIONS.
● this process is known as FRACTIONAL DISTILLATION
● the compounds in each fraction have a particular range of boiling points and specific uses
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Steps in Oil Refining:
1) the crude oil is heated to about 400°C in a furnace then pumped into a distilling column (fractionating tower…often more then 100 ft tall!);
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Steps in Oil Refining:
2) the component substances of the crude oil vaporize – as they rise up the column, they recondense into liquids as they cool;
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Steps in Oil Refining:
3) trays are arranged at appropriate heights to collect the various fractions:
-the smaller, lighter molecules have lower boiling points and condense high in the column;
-the larger, heavier molecules condense lower in the column (at higher temps.)
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NOTES: A.4 – A Look At Petroleum’s
Molecules
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*in the refining process, some fractions never condense to the liquid state – they remain gases!
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Gaseous Fraction:
● the gaseous fraction includes:
compounds with LOW boiling points (less than 40°C)
small hydrocarbons (1 - 4 C atoms)
*why do they have such low boiling points?
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INTERMOLECULAR FORCES
● INTERMOLECULAR FORCES = forces of attraction between molecules
as a result of weak intermolecular forces (they are only slightly attracted to each other), these small hydrocarbon molecules readily separate from each other and rise through the distillation column as gases
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Liquid Fractions:
● the liquid fractions of petroleum (i.e. gasoline, kerosene, and heavier oils) include:
compounds with intermediate boiling
points
medium hydrocarbons (5 - 20 C atoms)
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Solid Fraction (Residue)
● the thick, sticky
residue fraction
(never vaporizes;
stays at the bottom) includes:
the largest hydrocarbons with the strongest intermolecular forces (why they never vaporize!)
these compounds are solid at room temp.
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