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Chemistry

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Chapter 3- Separation and Purification

A pure substance consists of a single element or compound.
Pure substances have a constant and fixed boiling and melting point.
Impurities cause variation in the melting and boiling points of the substance. Therefore, they can be used to determine if a substance is pure or not.
Different purification techniques can be used to separate and purify substances.

Method	Usage	Example
Filtration	Insoluble solid from liquid	Sand and water
Evaporation to dryness	Soluble solid from a solution	To get salt from salt solution
Crystallization	Pure solid from a solution	To get Copper (II) sulfate from water
Solvent in which only one solid is soluble	A Mixture of two solids	Sand and salt
Sublimation	Solid that sublimes with one which doesn’t	Iodine and sand
Magnet	Magnetic substance from a non-magnetic one	Iron filings and sulfur
Simple distillation	Pure solvent (liquid) from the solution	To get water from a salt solution
Separating funnel	Immiscible liquids	Oil and water
Fractional distillation	Miscible liquids with different boiling points	Water and ethanol
Chromatography	Components that dissolve in the same solvent	Different dyes
Centrifugation	Mixtures by spinning	Blood cells from plasma
Decanting	Liquid and insoluble particles	Rice from water

STEPS TAKEN DURING DISTILLATION:

Thermometer should be placed beside the sidearm of the distillation flask, not inside the liquid.
Water outlets should be positioned in the correct way with cold water in from the bottom and leaving from the top.
The condenser slopes downward so the pure solvent runs to the flask/beaker.
If the distillate is volatile, it has to be kept in a container containing ice so it doesn’t evaporate.

Chromatography

Different components separated using chromatography have distinct Rf values or Retention factors.
Rf value is calculated by dividing the distance moved by the solute by the distance moved by the solvent.
Rf values can be matched by the already known values to identify the component.
Sometimes, the components are transparent such as amino acids. A locating agent (e.g. Ninhydrin) is sprayed on the chromatogram to make them visible.