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2.2.2 Separation Techniques - Coggle Diagram
2.2.2 Separation Techniques
Simple Distillation
Methods of Purification
All methods rely on there being a difference of some sort, usually in a physical property such as boiling point, between the substances being separated
Five common techniques are distillation, fractional distillation, filtration, crystallisation and chromatography
The choice of the method of separation depends on the nature of the substances being separated.
Simple Distillation
This is used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids
The solution is heated, and pure water evaporates producing a vapour which rises through the neck of the round bottomed flask
The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
After all the water is evaporated from the solution, only the solid solute will be left behind
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Filtration
A piece of filter paper is placed in a filter funnel above a beaker
Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g., sand from a mixture of sand and water)
Centrifugation can also be used for this mixture
A mixture of insoluble solid and liquid is poured into the filter funnel
The filter paper will only allow small liquid particles to pass through as filtrate
Solid particles are too large to pass through the filter paper so will stay behind as a residue
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Fractional Distillation
This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
The solution is heated to the temperature of the substance with the lowest boiling point
This is used to separate two or more liquids that are miscible with one another (e.g., ethanol and water from a mixture of the two)
For water and ethanol
The mixture is heated until it reaches 78 ºC, at which point the ethanol boils and distills out of the mixture and condenses into the beaker
Ethanol has a boiling point of 78 ºC and water of 100 ºC
When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated
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Crystallisation
The saturated solution is allowed to cool slowly
Crystals begin to grow as solids will come out of solution due to decreasing solubility
Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution
If the solution is saturated, crystals will form on the glass rod
The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind
The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water)
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Paper Chromatography
If two or more substances are the same, they will produce identical chromatograms
If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
This will show the different components of the ink / dye
An impure substance will show up with more than one spot, a pure substance should only show up with one spot
Different substances have different solubilities so will travel at different rates, causing the substances to spread apart
Those substances with higher solubility will travel further than the others
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The solvent travels up the paper by capillary action, taking some of the coloured substances with it
The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container
A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples
This technique is used to separate substances that have different solubilities in a given solvent (e.g., different coloured inks that have been mixed to make black ink)