Separation Techniques

Physical methods

• Filtration
• Evaporation
• Distillation
• Magnetic attraction
• Paper chromatography

Each method uses the difference in the physical property between the constituents to separate them.

Filtration:

Filtration is the most straightforward method of separating a suspension of an insoluble solid from a liquid or solution.

Items needed for filtration:

1. Beaker
2. Filter funnel
3. Filter paper (Filter paper contains many small pores invisible to the naked eye. The pores allow liquid/solution to pass through while big particles are trapped.)
4. Container containing the mixture

Procedure:

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Place the filter funnel over the conical flask.
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Fold the filter paper into the shape of a cone and place it inside the filter funnel.
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Moisten the filter paper with deionisedwater (distilled water)
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Pour the mixture into the filter funnel slowly.
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Residue and filtrate are obtained.

Evaporation to Dryness

Evaporationis a possible method for obtaining the solute from a solution.

When a solution is heated, the solventevaporates, leaving behind the dissolved solids as residue.

This method is used to separate dissolved solids from a solution.

When a solution containing dissolved solutes is heated, the solvent will evaporate. Only the solute (residue) will remain in the evaporating dish.

Evaporation to dryness cant be use for solutions like sugar solution cause the Sugar will decompose upon heating.

Crystallisation

Crystallisation separates a dissolved solid from a solution as well-formed crystals. Its another method to separate solvent and solute that evaporation to dryness cant separate like the sugar solution.

How does it work?

Crystallisation work as solubility of solutes decreases as temperature decreases and because hot solution cools, it becomes saturated(can no longer hold more solute). Extra solute that cannot be dissolved separates as pure crystals.�Extra solute that cannot be dissolved separates as pure crystals.

Procedure
1. Heat the solution to evaporate some of the water to obtain a hot and saturated solution.

2. Allow the solution to cool. As less solute is dissolved at lower temperature, crystals are formed on cooling.

3. Filter the crystals. Wash the crystals with a little cold deionised water and dry them by squeezing them between sheets of filter paper.

Distillation

Distillation is used to separate a pure liquidfrom a solid-liquid or liquid-liquid mixture.

2 procedure is involved during distillation:

• �BoilingBoiling
• Followed by Condensation

There are two kinds of distillation

1st one is: simple distillation

2nd one is: fractional distillation

simple distillation

• Process of obtaining a pure liquid (solvent) from a solution (solute+ solvent).
• The solution is boiled until the liquid (solvent) reaches its boiling pointwhen it changes into a gas.
• The vapourtravels to the condenser and condenses to form the pure liquid which is collected as the distillate.

fractional distillation

Used to separate two or more miscible liquids
*Miscible liquids: liquids that are completely solublein each other

• Fractional distillation has a fractionating columnthatseparates liquids in order of boiling points.
• The liquid with the lowestboiling pointboils first and its vapourtravels up the fractionating column,condenses in the condenser and is collected as distillate.

Reverse Osmosis

• Reverse osmosis is used for desalination
• Sea water is pre-treated to remove debris and contaminants
• It is then pumped at high pressurethrough partially permeable membranes
• This removes all traces of bacteria, viruses, chemicals and dissolved minerals

 

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