Methods of Separating & Purifying SubstancesEdexcel GCSE Chemistry: Flashcards

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In chemistry, what does 'pure substance' mean?

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In chemistry, what does 'pure substance' mean?: A single element or compound, not mixed with any other substance.
How does the melting behaviour of a pure substance differ from a mixture?: A pure substance melts sharply at one exact temperature; a mixture melts over a range of temperatures.
What separation technique separates an insoluble solid from a liquid?: Filtration.
What separation technique separates a soluble solid from a solution?: Crystallisation — evaporating solvent until saturated, then cooling to form crystals.
What is the difference between simple and fractional distillation?: Simple distillation separates a solvent from a solution; fractional distillation separates two or more miscible liquids with different boiling points.
In paper chromatography, what are the mobile phase and stationary phase?: The mobile phase is the moving solvent; the stationary phase is the paper.
How is the Rf value calculated?: Distance travelled by the substance divided by distance travelled by the solvent.
How can you tell from a chromatogram whether a substance is pure?: A pure substance produces only one spot; a mixture produces multiple spots.
What three processes make waste and ground water potable?: Sedimentation, filtration, and chlorination.
How is sea water made potable?: By distillation, which removes dissolved salts.
Why must water used in chemical analysis contain no dissolved salts?: Because dissolved salts could interfere with or contaminate the results of the analysis.
What core practical uses simple distillation and paper chromatography together?: Investigating the composition of inks.