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Topic 3 (CHEM) - Separation and Purification (Decanting / Separating…
Topic 3 (CHEM) - Separation and Purification
Decanting / Separating Funnel
E.g. Oil and water
Used to separate two immiscible liquids
[Process]
The liquid with the lower density floats on top
When the tap is opened, the liquid with the higher density flows through the funnel into the collecting container
The tap is closed just before the liquid with the lower density starts to flow
Magnetic Attraction
Used to separate a magnetic and non-magnetic material
E.g. Iron and sulfur separated by magnetic
Filtration
Used to separate an insoluble solid from a liquid
E.g. Water and Sand
Evaporation
Used to separate solvent from solute in a solution
E.g. Salt and Water
Crystallisation
Used to separate a solid that has dissolved in a liquid
E.g. Copper (II) Sulfate Solution - form copper(II)sulfate crystals from H20
E.g. Form sugar crystals from sugar solution
Sublimation
Used to separate materials that can sublime from materials that cannot sublime
E.g. Ammonium, Chloride, Iodine, Carbon Dioxide (dry ice)
E.g. To separate mixture of iodine and sand, heat it up
Simple Distillation
Used to separate two liquids with a sufficient difference in boiling points
E.g. Water (100ºC) and Ethanol (78ºC)
[Process]
On boiling, the liquid with the lesser boiling point, it's vapour rises, and enters the Liebig condenser, where it is cooled by the cold water jacket
The condenser has a jacket of cold water. The coldest water enters at the bottom of the jacket, circulates and exits at the top.
In this way, it is ensured that the coldest part of the condenser is just before the vapour passage
With the inlet at the bottom, the temperature of the circulating water will be lower at the bottom than at the top, allowing more vapour to be condensed.
Condensed liquid is called the
distillate
. This drips into the conical flask as pure liquid
If the distillate is
volatile
, the conical flask is put in a large container of ice
This helps to keep the temperature of the distillate low so that it remains in liquid state.
Sometimes, porcelain boiling chips are placed in the mixture to smoothen the boiling (so that it will not be too vigorous)
Fractional Distillation
Used to separate 2 or more miscible liquids with very close boiling points
E.g. To separate pure N2 and pure O2 from liquid air / To separate the different components of crude oil (petroleum etc.)
[Process]
The liquid with the lowest boiling point will condense and distill first
The vapour of the liquid with the higher boiling point will condense along the fractionating column instead
Fractional Distillation has a fractionating column
filled with
glass beads / plates / spiral
Chromatography
Used to separate coloured components in a mixture (components are soluble in the solvent)
E.g. amino acids (biology) / pen inks
[Process]
Drop of mixture is added to bottom of filter paper
Different coloured components of a mixture move up the filter paper at different speeds
Eventually the components of the mixture are separated as distinct spots on the filter
Retardation factor (Rf) is the ratio of the
distance travelled by solute
to
distance travelled by solvent (usually water/alcohol)
If the dye travels further up the chromatograph, it has a higher solubility with that solvent