Monday, October 18, 2010

Separation Techniques

Separating mixtures
·         In order to separate mixtures you need to devise a process that separates components with different properties.
·         Some of these properties include:
o   High density/ Low density
o   Volatile/ Non volatile
o   Soluble/ Insoluble
o   Magnetic/ Non magnetic
o   Polar/ Non polar
·         The more similar the properties = the more difficult it is to separate them.
Some Basic Techniques
Hand Separation and Evaporation
·         Hand separation (solids and solids)
o   This is the most basic technique.
o   Magnets or sieves may also be used to separate mechanical or heterogeneous mixtures.
o   Ex.  A dry mixture of salt and sand.  *Note – manually picking out the sand does not change the chemical identity of the salt or the sand.
·         Evaporation (solid dissolved in a liquid solution)
o   Boil away the liquid and the solid remains.
                                                                  Example of Evaporation
·         Filtration (solids(not dissolved) and liquids)
o   Selects components by particle size. Liquid and gaseous components will pass through the filter while the solid particles will be retained.
o   Can use a porous filter or filter paper (residue left in filter paper, filtrate goes through filter paper)
Watch this youtube video on filtration!

·         Crystallization
o   A change happens to a mixture (either physical or chemical)
o   Solids are then separated by filtration or floatation. Remaining solid comes out as pure crystals and they are then filtered from the remaining solvent.
Youtube Time!

·         Gravity Separation (solids based on density)
o   A centrifuge whirls a test tube around at high speeds forcing the denser materials to the bottom.
o   Works best for small volumes

·         Solvent Extraction
o   A technique also called liquid extraction, used to separate liquids.
o   Separation of a substance from a mixture by dissolving that substance in a suitable solvent
o   Works best with solvents that only dissolve one component
o   Mechanical mixture: (solid and solid) use liquid to dissolve one solid but not the other so the desired solid is left behind or dissolved.
o   Solution: solvent is insoluble with solvent already present. Solvent dissolves one or more substances and leaves unwanted substances behind.
·         Distillation
o   (liquid in liquid)
o   Based on differences in volatilities in a boiling liquid mixture
o   Physical separation process. Not chemical.
o   The liquid with the lowest boiling temperature boils first- vapour ascents to distillation flask and enters condenser; gas cools and condenses back to liquid dropping the distillate as a purified liquid.
                                                                  Process of Distillation

·         Chromatography
o   Can separate very complex mixtures
o   Accurate and very precise
o   Separated components can be collected individually
o   Flow the mixture over a material that retains some components more than others, so different components flow over the material at different speeds
o   A mobile phase sweeps the sample over a stationary phase
·         Sheet Chromatography
o   Paper Chromatography (PC)
§  Stationary phase= a liquid soaked into a sheet or strip of paper
§  Mobile phase = a liquid solvent
§  Components appear as separate spots spread out on the paper after drying or “developing”
Youtube Time!

o   Thin layer Chromatography (TLC)
§  Stationary phase = a thin layer of absorbent coating a sheet of plastic or glass
§  Some components bond to the absorbent strongly; others weakly
§  As with paper chromatography components appear as spots on the sheet

By Candace

No comments:

Post a Comment