SEPARATION TECHNIQUES

SEPARATION TECHNIQUES

1. Separating Solid from liquid

   • Filtration
     • separate insoluble solid particles from a liquid
     • *residue, filtrate, filter paper, filter funnel
   • Evaporation to dryness
     • obtain a soluble solid from a solution by heating the solution until all the water has boiled off
     • Safety goggles must be worn
     • Evaporating dish, Wire gauze, tripod stand, bunsen burner
     • Solid obtained would still contain soluble impurities would still be left with the solid
   • Crystallisation
     • used for obtaining a pure solid sample from its solution
     • Heating stopped when a hot saturated solution is formed. The resulting solution cools to room temperature, dissolved solid then forms pure crystals
     • 1. Dissolve 2. Filtration 3. Evaporation to dryness

2. Separating a liquid from a solution

   • Simple distillation
     • Used to separate a pure solvent from a solution
     • *Distillation is the process of a liquid and condensing the vapour. Pure water can be obtained from a salt solution by distillation.
     • Steps: (1) Solution boils in the distillation flask. Boiling chips ensure smooth boiling. Water vaporises, rises and enter condenser--> (2) In the condenser, water vapour is cooled. Vapour condenses and changes back to pure water (distillate)--> (3) Pure water is collected as a distillate in the receiver (conical flask)

3. Chromatography

   • Paper Chromatography
     • Separating two or more components that dissolve in the same solvent
     • Chromatography paper with the separated components is called a chromatogram
     • (1) Draw a pencil lines at about 1cm from the bottom of the strip of filter paper or chromatography paper--> (2) Put a drop of the solution on the pencil line. Allow drop to dry--> (3) Dip the paper into a glass tank containing solvent, Ethanol that is soaked by paper will dissolve dyes--> (4) Ethanol will travel carrying the dyes along. The more soluble a dye is in ethanol, the higher it would go
     • Rf value: how far the solvent front and substance travel up the chromatogram depends on how long the experiment is allowed to run.

4. Separating Liquids

   • Separating funnels
     • Used to separate immiscible liquids
     • Separating funnel, tap, oil, water
     • Steps: (1)Pour mixture into separating funnel when tap is closed--> (2)Support separating funnel using a retort stand, place a clean beaker below the separating funnel--> (3)Allow the liquids to separate completely. The denser liquid will be the bottom layer--> (4) Open the tap of the funnel to allow the bottom layer to drain into the beaker. CLose the tap before the top layer of liquid runs out.--> (5) Place another beaker below the funnel. OPen the tap to allow a little of the top layer of liquid into the beaker. Dispose of the liquid collected. Now, the separating funnel contains only oil while the beaker from step 4 contains only water.
   • Fractional distillation
     • Used to separate a mixture of miscible liquids with different boiling point
     • Fractionating: attached to round-bottom flask. Many glass beads in the fractionating column providing a large surface area for vapour to condense on
     • *Refer to simple distillation
     • (1) The liquid with the lowest boiling point will distill first--> (2)The vapours of liquid with higher boiling points condense along the fractionating column and fall back into the round-bottomed flask