IGCSE›Oxford AQA IGCSE Chemistry›Mind mapsPure SubstancesOxford AQA IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat is pure?A single element or compoundNothing else mixed inOnly one type of particle throughoutEveryday 'pure' is not the chemistry meaningSharp pointsPure substances melt at one fixed temperatureThey boil at one fixed temperatureMixtures melt over a rangeImpurities lower the melting pointPure substancesone substance onlyTesting purityHeat a small sample slowly and steadilyRecord when melting starts and finishesCompare with the known value in data tablesSharp and matching → pureLow or gradual → impureWhy it mattersFoodstuffs — check for cheaper substitutesDrugs — impurities affect safety and effectBatches can be checked for contaminationExam tipsImpurity lowers melting point and widens the range'Pure milk' is still a mixture