Separation Techniques
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flagWhat you'll discover
- arrow_forwardChoose the correct separation technique from the properties of the components
- arrow_forwardSeparate sand, salt and water by filtration followed by evaporation
- arrow_forwardExplain sublimation and use it to separate naphthalene from salt
- arrow_forwardDescribe simple distillation and what the condenser does
- arrow_forwardRun a paper chromatogram and explain why dyes travel different distances
Match the technique to the property
Every separation exploits a difference in properties. Filtration works when one component is insoluble: the solid stays on the paper as the residue, the liquid passes through as the filtrate. Evaporation recovers a dissolved solid by boiling the solvent away — done gently in an evaporating dish, ideally stopping at the crystallisation point so crystals form slowly and large.
Sublimation is the special case for solids like naphthalene, camphor, iodine and ammonium chloride that pass directly from solid to vapour. Heat the mixture and the sublimable component rises as vapour and re-solidifies on a cold surface (an inverted funnel or watch glass), leaving the non-sublimable salt behind.
Distillation: when you want the solvent back
Evaporation throws the water away — distillation catches it. The solution boils in a distillation flask, the vapour rises into a water-cooled condenser, and pure liquid drips into the receiver. The thermometer sits at the side-arm junction, reading the vapour temperature: a steady 100 °C confirms pure water is coming over.
The condenser's cooling water enters at the bottom and leaves from the top, flowing against the vapour — this counter-current arrangement keeps the coldest water at the coldest end and condenses vapour most efficiently. Distillation separates salt from water completely: the salt cannot evaporate, so it stays in the flask.
Chromatography: separating the inseparable-looking
Black ink looks like one substance but is usually several dyes. In paper chromatography a spot of ink is placed on a pencil baseline just above the solvent level. As the solvent climbs the paper by capillary action, each dye is carried along at its own rate — dyes that dissolve better in the solvent and stick less to the paper travel further.
The result is a chromatogram: each dye becomes a separate spot. The ratio of distance moved by the spot to the distance moved by the solvent front is the Rf value, always between 0 and 1, and constant for a given dye in a given solvent — so Rf values identify substances. The baseline must be in pencil, since an ink baseline would chromatograph itself!