There are different ways to separate mixtures, including filtration, evaporation, chromatography and distillation.
Filtration
Definition
Filtration is when you separate an insoluble solid from a liquid.
Example
Mixture of sand and water. This mixture can be separated using filtration because sand is insoluble in water.
procedure
1.
Pour the beaker containing the sand and water mixture into the filter funnel.
2.
Water (liquid) particles are small enough to go through the pores of the filter paper and into the beaker. Sand (solid) particles are too large to pass through so remain on the filter paper.
Evaporation
Evaporation is used to separate a soluble solid from a liquid.
Example
Magnesium sulfate crystals are soluble in water. You can use evaporation to separate them because water evaporates leaving the magnesium sulfate crystals behind.
1.
Solution
2.
Evaporating basin
3.
Bunsen burner
4.
Concentrated solution
5.
Crystallised solute
procedure
1.
Place a gauze on the tripod.
2.
Place a solution in an evaporating basin and heat using a Bunsen burner.
3.
Volume of solution will decrease and crystals will become visible at the bottom of the evaporating basin.
4.
Remove the evaporating basin with a pair of tongs. Caution: hot!
Paper chromatography
Paper chromatography is used to separate dissolved substances from one another.
Example
Paper chromatography can be used to separate dyes in ink.
1.
1cm height
2.
Base line
3.
Beaker
4.
Solvent
5.
Watch glass
PROCEDURE
1.
Draw a pencil line 1cm above the bottom of the chromatography paper.
2.
Put spots of inks along the line ensuring they are not too close to each other.
3.
Place chromatography paper inside a beaker containing solvent.
4.
Cover beaker with a watch glass.
5.
Solvent will seep up the chromatography paper taking some the dye with it.
6.
Different dyes in the ink will travel up with the solvent at different speeds so will be placed at different points on the chromatography paper.
7.
Compare the pattern of spots of your unknown dyes with known references to identify which dyes are present
Simple distillation
Simple distillation is used to separate liquids from solids.
Example
Separating salt water.
1.
Flame
2.
Mixture of liquids
3.
Flask
4.
Thermometer
5.
Cooling water going out
6.
Condenser
7.
Cooling water going in
8.
Distilled water in the beaker
PROCEDURE
1.
Heat mixture in a round bottom flask. The water will boil, forming steam.
2.
The steam will become cool and turns back to a liquid inside the condenser.
3.
Liquid water is collected in a beaker or vial.
4.
Salt is left behind in the flask.
Checking for purity
Pure chemical substances have fixed melting and boiling points. Substances can be identified by finding out the boiling or melting point and comparing it to reference values. If impurities are present it will change the melting and boiling point, so you can easily identify whether impurities are present or not.
Example
Pure water boils at 100°C. If you want to see if you have separated a mixture and obtained pure water measure the boiling point. If it boils at 100°C, it is pure water. If not, there are impurities present in the water.
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Changes of state
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Reversible changes and separation methods
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Separating mixtures
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FAQs - Frequently Asked Questions
How can we check if a substance is pure?
Purity of a substance can be checked by identifying the melting and/or boiling point. This is because pure chemical substances have fixed melting and boiling points. Impure substances will differ from the known reference values.
What is filtration?
Filtration is a physical method used to separate an insoluble solid from a liquid.
What is evaporation?
Evaporation is a physical method used to separate a soluble solid from a liquid.
