Sunday, October 17, 2010

How to Separate Mixtures (by Bev)

-basis: different components & properties
-come up with a process that differentiates between components with different properties
     ex. high density/low density

-a substance comprised of more than one substance that is not chemically bonded
-the mixture’s components keep their identities
-the more different the properties are, the easier it is to separate them

-filtration: chooses components by particle size
-flotation: chooses components by density
-crystallization & extraction: chooses components by solubility
-distillation: chooses components by boiling point
-chromatography: chooses & absorbs components at different rates in a fluid mixture
Hand separation
-for solids
-mechanical/heterogeneous mixture can be separated with magnet/sieve
-evaporation: a solid dissolved in a liquid solution
                -liquid evaporates (from boiling) & the solid is left
-for solids that are not dissolved in liquids
-using a permeable filter, pass a mixture with solid particles through
-the solid particles stay on top of the filter because they are bigger than the pores
Filtration Apparatus Diagram
-the filtrate permeates but the residue remains in the filter
-a solid in a liquid
-precipitation: from physical/chemical change, a solute (dissolved substance) is converted into a solid
-flotation/filtration separate the solids
-the desired solid becomes a saturated solution, containing the maximum amount of solute (which the liquid can no longer dissolve
-evaporate/cool: solid becomes pure crystals, which are filtered
Gravity separation
-for solids based on density
-centrifuge rapidly spins a test tube & separates substances of different densities, forcing the denser materials to the bottom
-works best with small quantities
Solvent extraction
-a component moves to a solvent shaken with a mixture
-works best with solvents that dissolve only one component
-mechanical mixture (2 solids): only one solid dissolves in the liquid & the desired solid is left behind
-solution: the solvent is insoluble because it is already present.  It dissolves at least 2 substances & the unwanted substances remain
                -if shaken in the separatory funnel, the liquids from layers
-for a solution of 2 liquids
-heating the mixture triggers the low-boiling components to volatize (vapourize)
-evaporated components collect & condense
-the liquid with the lowest boiling point boils first, the vapour ascends to distillation flask & enters condenser, gas cools to a liquid, & distillate (condensed liquid formed from boiling) is dropped as a purified liquid
-a mixture is passed over a material that absorb some components more than others
-different components pass over the material at different speeds
-mobile phase: sweeps the sample over the stationary phase (ex. Wind sweeping swarm of bees over flower bed)
-can separate extremely complex mixtures
                Ex. Drugs, plastics, flavourings, foods, pesticides
-using very small sample sizes, the analysis can be highly accurate & precies
-the separated components can be collected individually
Sheet/paper chromatography
-stationary phase is a liquid soaked into sheet of paper & mobile phase is a liquid solvent
-some components spend more time in the stationary phase than others
-components appear as separate spots spread out on the paper after drying/”developing”
Thin layer chromatography
-the stationary phase is a thin layer of absorbent (often SiO2 or Al2O3) coating a sheet of plastic/glass
-some components bond to the absorbent strongly; others, more weakly
-components appear as spots on sheet

Practice Problems: Separate!
1)      Coins: by hand
2)      Sand & copper sulphate: solvent extraction with filtration
3)      Salt in water: evaporation/distillation
4)      Sulphur 8 iron fillings: magnet (by hand)
5)      Ink: chromatography

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