Separation techniques Objectives To understand the key separation

Separation techniques

Objectives �To understand the key separation techniques used to separate mixtures

Key terms �What do these mean? �Solvent �Solute �Solution �You must be able to use these confidently

Separating mixtures �Which mixtures do we need to separate?

How can we separate mixtures? �Any suggestions?

Filtration �Example: Water filtration

Principles �Insoluble solids separated from fluid: �Solid particles too large to pass through holes �Fluid particles small enough to pass through holes. �Solid trapped in filter �Fluid passes through. �N. b. Fluid = liquid or gas

Chromatography �Example gas chromatography:

Principles �Separates mixtures of chemicals that can be dissolved in a liquid medium or vaporised in an inert gas medium. �Dissolved or vaporised substances rise up the paper or column. �The height to which they rise is dependant on their particle size/mass. �Smallest particles rise further thus separating the constituent parts of the mixture.

Magnetic separation �E. g. the separation of iron from its ore:

Principles �Iron in rich ores is magnetic; �Iron ore is crushed. �Iron rich material is attracted to the magnet; �Other parts of the ore containing little or no iron are washed away. �Left with iron that can be purified. �Only works on high grade ores

Distillation/fractional distillation �E. g. the fractional distillation of crude oil

Principles �Separates mixtures of two or more liquids; �Each liquid has a different evaporation point; �As the mixture is heated it stays at the boiling point of the lowest liquid until this has boiled off; �It then rises to the boiling point of the next liquid. �Used to distill spirits, components of air and of crude oil.

Centrifugation �E. g. separating the Parts of the cell

Principles �Mixture is spun in a centrifuge at great speeds; �Extreme forces cause suspended solids to separate out; �The amount of force applied and length of time affects the size of the particle that sediment; �The smaller the particle, the higher the force needed. �Liquid on top of the sediment can be decanted off.

Decanting �E. g. to separate oil and water

Principles �Can separate two immiscible liquids; �Liquids that separate out of a mixture because their particle repel each other; �Liquids of different densities. �Can be used to separate solids from liquids, e. g. the supernatant is decanted from a centrifuged sample

Evaporation e. g. salt pans

Principles �Solid dissolved in a solvent to create a solution; �Solvent evaporates off; �Solute crystallises to form a solid that remains behind.

Electrophoresis �E. g. to separate proteins

Principles �An electric current is used to separate components of mixture �Current attracts charged particles along a gel �Lighter particles travel further �Is like chromatography only using charged particles and electricity; �Used to separate proteins; �A very important tool in working out evolutionary relationships between species.

Mixtures �Heterogeneous �All particles are equally distributed throughout the mixture, e. g. air and blood �Heterogeneous �Particles are not equally mixed throughout but are indifferent concentrations in different areas, e. g. soil, a lake, a tiramisu

Particle models �In your groups produce a particle model for one of the above mentioned separation techniques: �Filtration Chromatography �Magnetic separation Fractional distillation �Electrophoresis Evaporation �Decanting Centrifugation �Make sure your diagram shows all steps and shows the make up of the mixture at the beginning.

Questions �Why do we do chromatography? �Give an example of distillation �How might you obtain a dissolved solid from its solvent �Why might filtration be useful? �How might a hospital technician separate blood? �How does electrophoresis separate proteins?