Separation techniques
Objectives
To understand the key separation techniques used to separate mixtures
Key terms
What do these mean?
SolventSoluteSolution
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
holesFluid particles small enough to pass through
holes.Solid trapped in filterFluid 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 theParts 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 gelLighter particles travel furtherIs like chromatography only using charged
particles and electricity;Used to separate proteins;A very important tool in working out
evolutionary relationships between species.
Mixtures
HeterogeneousAll particles are equally distributed
throughout the mixture, e.g. air and blood
HeterogeneousParticles 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 ChromatographyMagnetic separation Fractional
distillationElectrophoresis EvaporationDecanting 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 distillationHow might you obtain a dissolved solid from
its solventWhy might filtration be useful?How might a hospital technician separate
blood?How does electrophoresis separate proteins?
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