硬度

硬度实验时间安排实验课前采集水样（宿舍开水、矿泉水、湖水），先用水样洗矿泉水瓶子，每人装约半瓶，上课时带来。老师会采湖水。每个同学测3个样品：开水、矿泉水、湖水。上实验课时，先称滤膜，对比与预实验时的数据。集中听硬度实验讲解。分头做硬度实验。2.6.DeterminationofTotalHardnessPurpose:TounderstandtheprincipleofhardnessmeasurementTomasteroneofthevolumetricmethods,complexationtitration.Whatishardness?TotalhardnessisthetotalconcentrationofCaandMginwater,whichincludescarbonatehardnessandnon-carbonatehardness.Whatistemporaryhardness?CarbonatehardnessisequaltotheamountofCaandMgcarbonateorbicarbonate,canberemovedbyboiling.Ca(HCO3)2CaCO3＋CO2＋H2OMg(HCO3)2MgCO3＋CO2＋H2OWhatishardness?Whatispermanenthardness?non-carbonatehardnesscontainschloride,sulfate,ornitratecannotberemovedbyboilingComplexationtitration1.EBT,ablueindicatorCa/Mg+EBT,purple-redcomplex2.TitratewithEDTACa/Mg-EBT,lessstableCa/Mg-EDTA,morestable3.AttheendpointCa/Mg-EDTA,colorlessFreeEBT,lightblue4.Colorturning:purple-redlightblueSamples3samplesforeachstudent:TapwaterDrinkingwaterLakewaterNote:Ifthesamplevolumeisdouble,adddoublebuffer