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?