Separation Techniques

• The components of a mixture can be separated by physical means and the method is determined by the physical properties, such as density, particle size, solubility, magnetism and sublimation.
• Separation Techniques:

  • Filtration
  • Evaporation and Crystallization
  • Simple Distillation
  • Fractional Distillation
  • Separating Funnel
  • Chromatography
• Filtration is used to separate an insoluble solid and liquid mixture based on particle size. It is done by using a funnel and filter paper which holds back the solid particles (called the residue) and letting the liquid particles pass through (called the filtrate). Examples: coffee machine and purification of drinking water

  
• Evaporation is used to separate a dissolved solid from a liquid where the boiling point of the liquid is lower than the solid. The process involves heating the solution until it evaporates leaving behind the substance with the lower boiling point. This allows for only the collection of the solid. Example: salt from seawater

  
• Crystallization, like evaporation, is used to separate a dissolved solid from a liquid where the boiling point of the liquid is lower than the solid. The solid left has a distinct crystalline structure. It is used if a hydrated solid containing water of crystallization is required.

  
• Distillation is a purification process where the components of a liquid mixture are vaporized and then condensed and isolated. It allows both the solid and the liquid to be collected.
• Simple Distillation is used to separate a soluble solid and liquid where the boiling point of the liquid is lower than the solid. But in this, both the liquid and solid can be collected.

  • The mixture is heated in the distillation flask until vaporized
  • The vapour rises from the flask and condenses in the Liebig condenser (collected as the distillate)
  • When most of the liquid is vaporized, the solution is poured into an evaporating basin.

  
• Fractional Distillation is used to separate a mixture of liquids into two or more liquids with different boiling points.
• Method of Fractional Distillation:

  • The mixture boils and the vapours of both liquids move up the fractionating column where they condense and vaporize many times
  • As the mixture of vapours moves up the column, it becomes richer with the vapour with a lower boiling point until the top of the column only consists of this vapour.
  • This vapour passes into the condenser, condenses and is collected as the distillate.
  • The vapour with the higher boiling point condenses in the fractionating column and returns to the flask and then distilled in a third container

  
• Separating Funnel is used to separate a mixture of two or more liquids that have different densities, hence they do not mix. The liquid with the lower density with float above the one with the higher density

  • The tap is opened to allow the liquid with the higher density to run into the container below then the tap is closed again
  • The tap is opened again to allow a very small amount of the liquid with the lower density to run into the second container

  
• Chromatography is used to separate a mixture of coloured dissolved substances based on their different solubilities and attraction to the paper they will be travelling.

  • The drop of dye mixture is placed 1 cm from the bottom of the rectangular paper. The paper is then hung in a beaker containing the solvent, which moves up the paper carrying the dyes with it.
  • The dyes that are most soluble and least attracted to the paper travel the fastest and further distance, while the dyes that are least soluble and more attracted to the paper travel the slowest and shortest distance

  
• Magnetic separation is a separation technique based on the differences in the magnetic properties of the substances. It is a technique used to separate magnetic solids, like iron, from nonmagnetic solids, like sand.

  
• Decanting is used to separate an insoluble solid from a liquid. It is simply to pour off of the upper liquid layer in another container while the solid stays at the bottom.

  
• Centrifugation is used to separate solids from liquids, or separate two liquids based on density. It involves the use of the centrifugal force. More dense components migrate away. Solid particles remain on the bottom. It is then followed by decantation.

  
• Uses of centrifugation:

  • Used in diagnostic laboratories for blood and urine tests.
  • Used to separate butter from cream.
  • Used in washing machines to squeeze water from wet clothes.
• Uses of chromatography:

  • To separate colours in a dye.
  • To separate drugs from blood.
• Uses of fractional distillation:

  • Separation of different fractions from petroleum products.
  • Separation of a mixture of methanol and ethanol