SS1 Chemistry Lesson Note on Standard Separation Techniques for Mixture

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TOPIC: STANDARD SEPARATION TECHNIQUES FOR MIXTURE

CONTENT:

1. SEPARATING A SOLUBLE SOLID FROM A LIQUID,
2. SEPARATING A MIXTURE OF TWO OR MORE LIQUIDS,
3. SEPARATING FUNNEL
4. CHROMATOGRAPHY

PERIOD 1: SEPARATING A SOLUBLE SOLID FROM A LIQUID:

1. FRACTIONAL CRYSTALLIZION:

This is a method used to separate a mixture containing different soluble solid solutes in a liquid. The solubility of the different solid solutes in the given solvent must differ at different temperatures. The process of separation is the same as in crystallization process. While cooling the solution crystals of the relevant solid solutes will come out of the solution leaving behind the others which are still within their limits of solubility.

2. PRECIPITATION (PHYSICAL): There are physical and chemical separation techniques involving precipitation.

In physical precipitation, two solids that are soluble in the same solvent are separated by the addition of another solvent in which one of the solids is insoluble, e.g. an aqueous solution of common salts (sodium chloride) and green vitriol( a compound of iron). It is a method used to separate a solid which has a difference in solubility in two different miscible liquids. For example, ethanol and water are two miscible liquids. Iron(II) tetraoxosulphate(VI) is soluble in water but not in ethanol. On addition of ethanol to a solution containing a mixture of iron(II) tetraoxosulphate and water, the iron(II) tetraoxosulphate(VI) will be precipitated out and can be separated by filtration.

PERIOD 2: SEPARATING A MIXTURE OF TWO OR MORE LIQUIDS

1. DISTILLATION

Distillation is the evaporation of water or other liquids from a solution and its recovery on a pure state by condensation. The method of distillation is used to recover a solvent (liquid from a solution mixture). That is, a pure liquid from an impure liquid (mixture). The apparatus used are shown in the diagram below.

(a) Simple distillation process

A mixture of two liquids with widely differing boiling points can be separated by evaporating one from the other and re-condensing it in a separate vessel. The process is called simple distillation.

Distillation is carried out by condensing the vapour, using a condenser. The vapour which is condensed and collected in a separate vessel is called the distillate.

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