Chapter 3: Separation Techniques

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Chapter 3 Separation Techniques

• You will learn about
• Pure substances
• Methods of purification
• - Chromatography
• - Filtration
• - Crystallization
• - Distillation

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How do we know which are the real products?
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Testing for Purity
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(i) Chromatography

• A technique using a solvent to separate a mixture
  into its components.
• E.g separate dyes in ink, detect traces of banned
  food substances, identify poisons or drugs.

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Procedure

• Food colouring is applied to chromatography
  paper.
• The paper is dipped into a solvent.
  (e.g water, alcohol)
• The solvent travels up the paper, dissolving and
  carrying the dye along with it.
• Coloured spots are seen in different positions on
  the paper at the end of results.

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Who wrote the ransom note?
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Culprit
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Ben Johnson stripped from his Olympic goldin
1988.
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ii) Filtration separating a solid from liquid
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• A mixture is poured into the filter funnel lined
  with filter paper.
• Liquid particles are small enough to go through
  the pores of the filter paper but the solid
  particles are too large to go through.
• Collect the filtrate that passes through the
  filter paper in a conical flask. The solid that
  remains in the filter paper is called residue.

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iii) Evaporation to Dryness Crystallisation
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Procedure
1. Pour some distilled water into the mixture to
dissolve the soluble substance. 2. Filter the
mixture. 3. Wash the residue with a little
distilled water to remove all the salt solution
from it. The residue is sand.
4. Evaporate the filtrate to dryness. Salt is
recovered.
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iv) Distillation separating a liquid from a
solution
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Procedure

• Solution is heated in a flask until the solution
  boils.
• Pure liquid turns into a vapour and leaves the
  flask
• Vapour is then cooled by a condenser, which
  changes it back into a liquid
• Liquid is called the distillate and is collected
  in a conical flask.

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How does simple distillation work?
2. In the condenser, water vapour condenses.
3. Pure water is collected as distillate.
1. In the distillation flask, water boils and
enters the condenser.
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SAFETY MEASUREMENTS
Thermometer
This ensures that the thermometer measures the
boiling point of the substance that is being
distilled.
Boiling Chips
To ensure smooth boiling.
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If the distillate is volatile, the receiver can
be put in a large container filled with ice.
This helps to keep the temperature of the
distillate low so that it remains in the liquid
state.
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Eg. Finding out the dyes present in sweets
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Paper chromatography

• a method of separating identifying mixtures.
• a suitable solvent is used.

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• Purity of Substances
• pure substances have fixed melting and boiling
  points
• melting points and boiling points are changed by
  the presence of impurities

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