GCSE›Edexcel GCSE Chemistry›Mind mapsMethods of Separating & Purifying SubstancesEdexcel GCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsPure or mixture?Pure: a single element or compoundMixture: not chemically combinedPure substance has a sharp melting pointMixture melts over a rangeTechniquesFiltration: insoluble solid from liquidCrystallisation: soluble solid from solutionSimple distillation: solvent from solutionFractional distillation: miscible liquids by boiling pointChromatographyMobile phase is the solventStationary phase is the paperPure substance gives one spotCompare with reference substancesSeparatingand purifyingRfRf valueRf=distance by substancedistance by solventR_f = \frac{\text{distance by substance}}{\text{distance by solvent}}Rf=distance by solventdistance by substanceCompare with known Rf values to identifyPotable waterPotable = safe to drink, not pureSedimentation, filtration, chlorinationChlorine kills microorganismsSea water: distillation removes saltsAnalysis water needs no dissolved saltsExam tipsUse the chemistry meaning of pureSay it melted over a range, so impure