Separation Techniques

Chapter Four
Separation Techniques

Pure and Impure substances
A pure substance is made up of only one substance and is not mixed with any other substance.
A mixture is a substance that contains two or more substances that are not chemically combined.
Purity of a substance can determined by testing its melting and boiling points or chromatography.

Fixed Melting & Boiling points
Fixed boiling point
Fixed melting point
A pure solid will melt completely at a fixed temperature.
Impurities lower the melting point of a substances.
Impurities cause melting to occur over a range of temperatures.
A pure solid will boil at an exact and fixed temperature.
Impurities higher the boiling point of a substances.
Impurities cause boiling to occur over a range of temperatures.

Separation Methods

Difference in properties enable the separation methods to work

Separating compounds with same properties
Chromatography
Apply a spot of food colouring to the chromatography paper. Dip the chromato-graphy paper in ethanol.
Ethanol dissolves the dyes and travels up the paper, carrying the dyes along.
Coloured spots are left in different places of the paper depending on the solubility of the dye in ethanol.

Separating insoluble solids from a liquid
Filtration
Place a piece of filter paper in a filter funnel. Position a beaker under the filter funnel.
Pour the mixture into the filter funnel. The liquid passes through the filter paper while the insoluble solids does not pass through.
The filtrate will be collected in the beaker and the residue remains on the filter paper.
Wash the residue with distilled water and let it dry. Separation is complete.

Separating dissolved solids from a solution
Crystallisation
Crystillisation applies to all substances while evaporation applies to substances that do not decompose when heated strongly.
Set up an apparatus of a beaker of the solution.
Apply heat under the beaker with a bunsen burner until a hot saturated solution is formed.
The solution is allowed to cool and the mixture is then filtered. Separation is complete.

Separating a solvent from a solution
Simple Distillation
Place a distillation flask under a bunsen burner and connect it to a condenser. Cold running water is allowed to enter from the bottom condenser and leave from the top.
Allow the condenser to slope downwards towards a beaker where the distillate is collected.
Heat a distillation flask with the solution together with porcelain chips until it boils.
Pure solvent is collected in the beaker.

Separating miscible liquids
Fractional Distillation
Place a distillation flask under a bunsen burner and connect it to a fractional column. The fractional column is connected to a condenser.
Cold running water is allowed to enter from the bottom condenser and leave from the top.
Allow the condenser to slope downwards towards a beaker where the distillate is collected.
Heat a distillation flask with the mixture together with porcelain chips until it boils.
The miscible liquid with a lower boiling point is collected.

Separating immiscible liquids
Separating funnel
Pour the mixture into the separating funnel.
Support the separating funnel using a retort stand and place the beaker below the funnel.
Allow the liquids to separate completely. The denser liquid will fall to the bottom.
Open the tap of the funnel to allow the bottom layer to drain into the beaker.
Close the tap when the liquid is fully drained.
Place another beaker below the funnel to collect a little of the top layer liquid so that the liquids are fully separated.

Separating a substance that sublimes from another with high melting point
Sublimation
Place the mixture in an evaporating dish. Position the dish under a bunsen burner.
Place an inverted funnel just above the dish.
The substance with high melting point would be left on the dish.
The other substance will vapourise and solidify when it lands on the surface of the funnel.

Separating magnetic objects from non-magnetic objects
Magnetic attraction
Place the mixture of magnetic and non-magnetic objects in a dish.
Place a magnet directly above the dish.
Magnetic objects will be attracted to the magnet while non-magnetic objects will be left on the dish.

Uses of techniques in daily life

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Separation Techniques

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