Separation Techniques

Separating Mixtures

• Basis for separation: different components and different properties.
• Strategy: Create a process that distinguishes between components with different properties.
  high/ low density polar/ non polar

Separation

• Components in the mixture retain their identities.
• The more similar the properties, the more difficult it is to separate them.

Basic Techniques

• Filtration
• Floatation
• Crystallization and Extraction
• Distillation
• Chromatography

Hand Separation

• Mechanical mixture/ heterogeneous mixture can be separated by using a magnet or sieve.

Evaporation

• Boil away the liquid and the solid remains

Filtration

• Mixture passes through a porous filter.
• Residue left in filter paper and filtrate goes through filter paper.

Crystallization

• Aspect of precipitation.
• Solids are separated by filtration or floatation.
• Saturated solution of desired solid
• Evaporate cool -> solid -> crystal (pure).
• Crystals are then filtered

Gravity Separation

• Centrifoge (machine that separates mixtures) whirls test tube around at high speed forcing denswer materials at the bottom.

Solvent Extraction

• Mechanical mixture - use liquid to dissolve a solid but not the other so the desired solid is left behind or dissolved.
• Solution - Solvent = insoluble with solvent already present

Distillation

• Heating mixture can cause low boiling component to vapourize.
• Then collect and condense vapourized components.

Chromatography

• Mixture flows over material that attracts some components more than the others, so different components flow over the material at different speeds.
• A mobile phase sweeps sample over a stationary phase.

Sheet Chromatography (Paper chromatography)

• Stationary phase is liquid soaked into sheet or strip of paper.
• Components appear as separate spots.

Thin layer chromatography (TLC)

• Stationary phase = thin layer of absorbent coating a sheet of plastic or glass.
• Some components attract to absorbent strongly; others weakly.