part 3-unit 1-Lesson3

化学化工专业英语SpecialtyEnglishforChemistryandChemicalEngineering主讲丁明洁河南城建学化工学院Part3/Unit1GeneralChemistryLesson3AnalyticalChemistry32009/081Gravimetry(重量法)2Titration（滴定法）3Extraction（萃取法）4Precipitation（沉淀法）(InsolubleSalts)（不溶解的盐类）ContentsfortodayIntroductionAnalyticalchemistryisthescienceofmakingquantitativemeasurements（定量测量）.Inpractice,quantifyinganalytes(分析物)inacomplexsamplebecomesanexerciseinproblemsolving.Tobeeffective（有效的）andefficient（有效率的）,analyzingsamplesrequiresexpertise（专业知识，专门技术）in:1.thechemistry（化学问题，化学过程）thatcanoccur（发生，出现）inasample2.analysisandsamplehandling（样品处理）methodsforawidevarietyof（多种多样的）problems(thetools-of-the-trade（贸易工具）)3.properdataanalysis（数据分析）andrecordkeeping（记录）Tomeettheseneeds,AnalyticalChemistrycourses（分析化学课程）usuallyemphasize（强调）equilibrium（平衡）,spectroscopic（光谱的）andelectrochemical（电化学的）analysis,separations,andstatistics（统计）Analyticalchemistryrequiresabroadbackgroundknowledgeofchemicalandphysicalconcepts.Withafundamental（基本的，根本的）understandingofanalyticalmethods,ascientistfacedwith（面临）adifficultanalyticalproblemcanapply（应用，申请）themostappropriatetechnique(s).Afundamentalunderstandingalsomakesiteasiertoidentify（鉴定，鉴别）whenaparticularproblemcannotbesolved（解决）bytraditionalmethods,andgivesananalyst（分析者）theknowledgethatisneededtodevelopcreative（创造性的）approachesornewanalyticalmethods.1.GravimetryGravimetryisthequantitativemeasurementofananalyte（被分析物）byweighing（称量）apure（纯的）,solidform（固态）oftheanalyte.Obtainingpuresolidsfromsolutions（溶液）containinganunknownamountofametalionisdonebyprecipitation（沉淀）.Sincegravimetricanalysis（重量分析法）isanabsolutemeasurement（绝对度量）,itisaprincipal（主要的，基本的）methodforanalyzingandpreparingprimarystandards（原基准，主基准）.Atypicalexperimentalprocedure（实验程序）todetermine（确定）anunknownconcentration（未知浓度）ofananalyteinsolutionisasfollows:quantitativelyprecipitate（使沉淀出）theanalytefromsolutioncollecttheprecipitatebyfiltering（过滤）andwash（冲洗）ittoremoveimpurities（杂质）drythesolidinanoven（烘箱）toremovesolventWeigh（称重）thesolidonananalyticalbalance（分析天秤）calculate（计算）theanalyteconcentrationintheoriginalsolution（原始溶液）basedontheweight（重量）oftheprecipitateGravimetricDeterminationofIron:Determineconstantweight（恒重）ofthecrucibles（坩锅）Oxidation（氧化）ofironsamplePrecipitation（沉淀）ofironhydroxide（氢氧化铁Ignition（点烯）ofironhydroxidetoironoxideDetermineconstantweightofthecruciblesplusironoxideCalculationofironinthesample2TitrationTitrationisthequantitativemeasurementofananalyteinsolutionbycompletelyreactingitwithareagentsolution（试剂溶液）.Thereagentiscalledthetitrant（滴定标准液）andmusteitherbepreparedfromaprimarystandard（基准）orbestandardized（使标准化）versus（对，相对于）aprimarystandardtoknowitsexact（精确的）concentration.Thepointatwhichalloftheanalyteisconsumed（被消耗）istheequivalencepoint（等当量点）.Thenumberofmoles（摩尔）ofanalyteiscalculatedfromthevolumeofreagentthatisrequiredtoreactwithalloftheanalyte,thetitrantconcentration,andthereactionstoichiometry（化学计量学）.Theequivalencepoint（等当量点）isoftendeterminedbyvisualindicators（指示剂）areavailablefortitrationsbasedonacid-baseneutralization（中和）,complexation（络和）,andredox（氧化还原）reactions,andisdeterminedbysometypeofindicator（指示剂，指示器）thatisalsopresentinthesolution.Foracid-basetitrations,indicatorsareavailablethatchangecolorwhenthepHchanges.Whenalloftheanalyteisneutralized,furtheradditionofthetitrantcausesthepHofthesolutiontochangecausingthecoloroftheindicatortochange.IfthepHofanacidsolutionisplotted（被策划为，对…做图）againsttheamountofbaseaddedduringatitration,theshapeofthegraph（图形）iscalledatitrationcurve（滴定曲线）.Allacidtitrationcurvesfollowthesamebasicshapes.StrongAcidTitrationCurveAtthebeginning,thesolutionhasalowpHandclimbs（上升，攀升，爬升）asthestrongbaseisadded.AsthesolutionnearsthepointwherealloftheH+areneutralized,thepHrisessharplyandthenlevelsout（水平，平衡）againasthesolutionbecomesmorebasicasmoreOH-ionsareadded.Manual（手动的）titrationisdonewithaburet（滴定管）,whichisalonggraduatedtube（带刻度的长管）toaccuratelydeliver（传递，释放，给出）amountsoftitrant.Theamountoftitrantusedinthetitrationisfoundbyreadingthevolumeoftitrantintheburetbeforebeginningthetitrationandafterreachingtheendpoint（终点）.Thedifference（差异）inthesereadingsisthevolumeoftitranttoreachtheendpoint.Themostimportantfactorformakingaccuratetitrations（进行精确滴定）istoreadtheburetvolumesreproducibly（可再现地）.Thefigure（数字，人物，图形）showshowtodosobyusingthebottomofthemeniscus（弯月面，半月面）toreadthereagentvolumeintheburet.Theendpointcanbedeterminedbyanindicator（指示剂）asdescribedaboveorbyaninstrumentalmethod（仪器方法）.Themostcommoninstrumentaldetectionmethodispotentiometric（电势测定的，电位计式的）detection.Theequivalencepointofanacid-basetitrationcanbedetectedwithapHelectrode（PH电极）.Titrations,suchascomplexation（络和）orprecipitation（沉淀）,involvingotherionscanuseanion-selectiveelectrode(ISE，离子选择电极).UV-visabsorptionspectroscopy（紫外吸收光谱）isalsocommon,especiallyforcomplexometrictitrations（络和滴定）whereasubtle（敏感的，精细的）colorchangeoccurs.Forrepetitive（重复的）titrations,autotitrators（自动滴定仪）withmicroprocessors（微处理器）areavailablethatdeliverthetitrant,stopattheendpoint,andcalculatetheconcentrationoftheanalyte.Theendpointisusuallydetect