Separation & Purification Techniques
Section: 12. Experimental Techniques & Chemical Analysis | Syllabus: Cambridge AS Level Physics 9702
Overview of Separation Techniques Why Separation is Important: In chemistry, we often need to separate mixtures into their individual components for analysis, purification, or use. Different separation techniques exploit different physical properties such as particle size, boiling point, solubility, and density.
Separation Technique A method used to separate the components of a mixture based on differences in their physical properties. Purification The process of removing impurities from a substance to obtain it in a pure form.
Summary of Separation Techniques Technique Property Used Used to Separate Example Filtration Particle size Insoluble solid from liquid Sand from water Crystallisation Solubility Soluble solid from solution Salt from salt solution Simple Distillation Boiling point Liquid from solution or mixture of liquids with very different boiling points Pure water from salt solution Fractional Distillation Boiling point Liquids with similar boiling points Crude oil into fractions; ethanol from water Paper Chromatography Solubility and attraction to paper Dissolved substances in a mixture Dyes in ink; amino acids Evaporation Boiling point Soluble solid from solution (when solid doesn't decompose on heating) Salt from seawater Decanting Density and settling Liquid from settled solid Water from sand after settling Separating Funnel Density and immiscibility Immiscible liquids (liquids that don't mix) Oil from water 1.
Filtration Filtration A separation technique used to separate an insoluble solid from a liquid by passing the mixture through filter paper, which traps the solid particles. When to Use: When you have a mixture of an insoluble solid and a liquid (e.g., sand and water, chalk and water).
Interactive Diagram: Labeled diagram showing filtration apparatus including filter funnel, filter paper folded into cone shape inside funnel, mixture being poured in, residue (solid) remaining on filter paper, and filtrate (liquid) collecting in beaker below.
Component Description Filter paper Porous paper with tiny holes that allow liquid through but trap solid particles Residue The solid that remains on the filter paper Filtrate The liquid that passes through the filter paper Method: Fold filter paper into a cone and place in a filter funnel Pour the mixture slowly into the funnel Liquid passes through; solid is trapped on the filter paper Collect the filtrate in a beaker below 2.
Crystallisation Crystallisation A separation technique used to obtain a soluble solid from a solution by evaporating some of the solvent to form crystals. When to Use: When you want to obtain pure solid crystals from a solution, especially when the solid might decompose if heated strongly during evaporation.
Method: Heat the solution gently to evaporate some of the solvent Stop heating when crystals start to form at the surface (saturation point) Leave the solution to cool slowly - crystals will form as solubility decreases Filter to collect the crystals Wash crystals with cold distilled water Dry the crystals between filter paper or in a warm oven Interactive Diagram: Step-by-step diagram showing crystallisation process: (1) heating solution in evaporating dish, (2) crystals forming at surface, (3) cooling dish with crystals forming, (4) filtering crystals, (5) drying crystals.
Should show crystal formation visually. Key Principle: Most solids are more soluble in hot water than cold water. By heating the solution and then cooling it, the solubility decreases and excess solid crystallizes out.
3. Simple Distillation Simple Distillation A separation technique used to separate a liquid from a solution by heating the solution to boil the liquid, then condensing the vapor back to liquid in a separate container.
When to Use: To obtain pure water from salt solution To separate liquids with very different boiling points (difference > 25°C) To purify a liquid by removing dissolved solids Interactive Diagram: Labeled diagram of simple distillation apparatus showing round-bottom flask with mixture being heated, thermometer at top of flask, Liebig condenser (water jacket with cold water in/out), distillate collecting in receiving flask.
Include arrows showing vapor path and water flow direction (cold in at bottom, warm out at top). Component Purpose Round-bottom flask Contains the mixture to be heated Thermometer Monitors temperature of vapor (should match boiling point of liquid being collected) Liebig condenser Cools vapor back to liquid; cold water flows through outer jacket Receiving flask Collects the purified distillate Heat source Heats the mixture to boiling point of desired liquid Process: Heat the solution in the flask The liquid with the lower boiling point evaporates first Vapor rises and enters the condenser Cold water in the condenser jacket cools the vapor back to liquid Pure liquid (distillate) collects in the receiving flask Non-volatile substances remain in the original flask 4.
Fractional Distillation Fractional Dist…
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