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 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?