IGCSE›Cambridge IGCSE Chemistry›Mind mapsWaterCambridge IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsTesting for waterAnhydrous cobalt(II) chloride: blue → pinkAnhydrous copper(II) sulfate: white → blueBoth change colour when hydratedName the colour it changes toPurity testsPure water melts at 0 °CPure water boils at 100 °CImpurities lower the melting pointImpurities raise the boiling pointBoils at 102 °C means not pureDistilled waterMade by boiling then condensing steamHas no chemical impuritiesStops unwanted side reactionsGives reliable resultsWatertests, purity, treatmentH2O0 °C100 °CNatural contaminantsDissolved oxygen is beneficial for fishMetal compounds can be essential or toxicPlastics and sewage are harmfulNitrates and phosphates cause eutrophicationWater treatmentSedimentation and filtration remove solidsActivated carbon removes tastes and odoursChlorination kills microbesChlorine prevents cholera and typhoidExam tipsSay which colour the test changes toExplain what impurities distilled water lacksNot all metal compounds are harmfulFor each stage, say what is removed and why