IGCSE›Oxford AQA IGCSE Chemistry›Mind mapsAlkalis & BasesOxford AQA IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat is a base?Neutralises an acid to give salt + waterMetal oxides and metal hydroxides are basesUsually insoluble solidsWhat is an alkali?A base that dissolves in waterReleases hydroxide ions, OHX−(aq)\ce{OH-(aq)}OHX−(aq)pH above 7All alkalis are bases, not all bases alkalisBasesand alkalisOH-NaOHKOHAmmoniaNHX3\ce{NH3}NHX3 is a gas that dissolves to give an alkaline solutionReacts with acid to make ammonium saltsNHX3+HNOX3→NHX4NOX3\ce{NH3 + HNO3 -> NH4NO3}NHX3+HNOX3NHX4NOX3Ammonium nitrate is a fertiliserLimewaterSolution of calcium hydroxideWeakly soluble, so an alkaliCO2 forms insoluble calcium carbonateTurns cloudy: test for CO2Exam tipsAn alkali must be solubleSay limewater turns cloudy/milky