沉淀滴定与重量分析.ppt

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,黄卫华：,027-68752149,13707133949,email:,whhuang,化南,324,研究方向,：,生命分析化学,单细胞分析,超微电极电化学,微流控芯片,神经信号传导探测,肿瘤转移模型,研究成果入选分析化 学经典教材,沉淀滴定与重量分析,Precipitation Titration,and,Gravimetric Analysis,Contents,1,微溶化合物的溶解度和溶度积,Solubility,and solubility product constant,2,沉淀滴定,Precipitation Titration,5.3,重量分析,Gravimetric Analysis,微溶化合物的溶解度和溶度积,Solubility,and solubility product constant,1.,Solubility(s),and solubility product constant,(,K,sp,),CaSO,4,(s),=Ca,2+,(aq)+SO,4,2-,(aq),K,sp,=Ca,2+,SO,4,2-,=9.1,10,-6,at 25,C,The equilibrium constant for the equilibrium established between a solid solute and its ions in a,saturated,solution.,1.1 Solubility(s)and solubility product,MA(,固,)MA(,水,)M,+,+A,-,M,+,A,-,MA,水,:,固有溶解度,(,分子溶解度,),用,s,0,表示,Solubility,:,s,=,s,0,+M,+,=,s,0,+A,-,K,ap,a,(M),a,(A),活度积常数,(,activity product constant,),只与,t,有关,S,(HgCl,2,)=0.25molL,-1,Hg,2+,=1.710,-5,molL,-1,s,0,solubility product constant and conditional solubility product constant,M,A,MA=M,A,K,sp,M A,M,M,A,A,=,K,sp,M,A,conditional solubility product constant,与条件有关,M,m,A,n,？,K,sp,K,sp,K,ap,solubility product constant,，与,t,、,I,有关,MA,2,:,K,sp,M A,2,=,K,sp,M,A,2,ap,sp,(M)(A),MA,(M),(A),K,a a,K,=,(M,),(A),Table Several Solubility Product Constants at 25C,Question,298K,时铬酸银,Ag,2,CrO,4,的溶度积常数为,2.010,-12,，求该温度下的溶解度。,Solution,设饱和溶液中 离子的浓度,x,mol/L,，则代入溶度积常数表达式得：,K,sp,(Ag,2,CrO,4,),=,c,(Ag,+,)/mol/L,2,c,()/mol/L,=(2,x,),2,x,=4,x,3,x,/moldm,-3,=,溶液中 离子的浓度为,7.910,-5,mol/L,也是,Ag,2,CrO,4,以,mol/L,为单位的溶解度。,Question,AgCl,和,Ag,2,CrO,4,的溶度积分别为,1.810,-10,和,1.1 10,-12,，则下面叙述中正确的是：,(A)AgCl,与,Ag,2,CrO,4,的溶度积相等,(B)AgCl,的溶解度大于,Ag,2,CrO,4,(C),二者类型不同，不能由 大小直接判断溶解度大小,Solution,分子式,溶度积,溶解度,/,AgBr,AgI,AgCl,mol dm,-3,1.810,-10,Ag,2,CrO,4,1.310,-5,5.010,-13,7.110,-7,8.310,-17,9.110,-10,1.110,-12,6.510,-5,1.2 Factors which affect,s,(1).,Salt effects increases s,沉淀重量法中，用,I,=0.1,时的,K,sp,计算,;,计算难溶盐在纯水中的溶解度用,K,ap,S,/,S,0,1.6,1.4,1.2,1.0,0.001 0.005 0.01,c,(KNO,3,)/(molL,-1,),BaSO,4,AgCl,I ,S,ap,sp,(M)(A),MA,(M),(A),K,a a,K,=,(M),(A),(2),The Common-Ion Effect in Solubility Equilibrium,同离子效应,The Common-Ion Effect,沉淀重量法总要加过量沉淀剂,.,例,:,测,SO,4,2-,若加入过量,Ba,2+,Ba,2+,=0.01molL,-1,S,=SO,4,2-,=,K,sp,/Ba,2+,=610,-10,/0.01=610,-8,molL,-1,m,(BaSO,4,)=610,-8,300233.4=,0.004mg,可挥发性沉淀剂过量,50%,100%,非挥发性沉淀剂过量,20%,30%,The Common-Ion Effect Decreases the Solubility,AgCl,在,KNO,3,溶液中的溶解度,(25,),0.00 0.00100 0.00500 0.0100,1.278 1.325 1.385 1.427,c,(KNO,3,)/mol/L,AgCl,溶解度,/10,-,5,(mol/L),0.15 0.24 0.016 0.014 0.013 0.016 0.023,c,(Na,2,SO,4,),/mol/L,S,(PbSO,4,),/mmol/L,PbSO,4,在,Na,2,SO,4,溶液中的溶解度,(25,),0 0.001 0.01 0.02 0.04 0.100 0.2000,(3).Acidic Effects,Increase s,例计算,CaC,2,O,4,在不同情况下的溶解度,CaC,2,O,4,Ca,2+,+C,2,O,4,2-,S,S,K,ap,(,CaC,2,O,4,)=10,-8.6,(,I,0,),H,2,C,2,O,4,p,K,a,1,=1.3 p,K,a,2,=4.3 (,I,0,),在纯水中,S,=Ca,2+,=C,2,O,4,2-,=510,-5,molL,-1,在,pH=1.0,的酸性溶液中,CaC,2,O,4,Ca,2+,+C,2,O,4,2-,S S,H,+,HC,2,O,4,-,H,2,C,2,O,4,用,I,0.1,的常数,K,sp,=,Ca,2+,C,2,O,4,=,S,2,=,C,2,O,4,2-,a,(H),K,sp,=,K,sp,=10,-7.8+3.4,=10,-4.4,(H),S,=10,-2.2,=610,-3,(molL,-1,),a,(H),=1/,=,1+H,+,b,1,+H,+,2,b,2,副反应系数,若,pH=4.0,，过量,H,2,C,2,O,4,(,c,=0.10molL,-1,),Ca,2,沉淀完全,K,sp,=,K,sp,a,=10,-7.8+0.3,=10,-7.5,(H),Ag,2,S,=2Ag,+,+S,2,2,S S/a,s(H),Ag,2,S,K,sp,8,10,-51,H,2,S p,K,a1,=7.1 p,K,a2,=12.9,pH=7.0,a,s(H),=2.5,10,7,Ksp=Ksp,a,s(H),=Ag,+,2,C,s,2-,=(2S),2,S=4S,3,S=1.1,10,-14,mol/L,K,sp,较大,S,2-,定量成为,HS,-,产生同量,OH,-,假设,MnS+H,2,O=Mn,2+,+HS,+OH,S S S,MnS,K,ap,10,-12.6,H,2,S p,K,a1,=7.1 p,K,a2,=12.9,检验：,OH,-,=,S,=10,-4.6,molL,-1,H,+,=10,-9.4,molL,-1,S(H),1,10,-9.4+12.9,+10,-18.8+20.0,1 +10,3.5,+10,1.2,10,3.5,S,2-,HS,-,H,2,S,主要以,HS,-,存在,故假设合理。,7.1,p,K,a,1,12.9,p,K,a,2,pH,S,2,H,2,S,HS,9.4,亦可不必计算，由优势区域图可知：,S,最小,同离子效应,络合作用,pCl=2.4,pCl,5 4 3 2 1 0,10,8,6,4,2,0,S,x10,6,mol/L,S,(AgCl)-pCl,曲线,(4).Complex effects increase s,K,sp,=Ag,Cl,-,=Ag,+,Cl,-,Ag(Cl),=,K,sp,(1+Cl,1,+Cl,2,2,+-,Ag,+,+Cl,-,AgCl,Cl,-,AgCl,AgCl,2,-,S,=Ag,=,K,sp,/,Cl,-,=,K,sp,(+,1,+Cl,2,+,H,+,Y,H,i,Y,H,PbC,2,O,4,=Pb,2+,C,2,O,4,2-,PbY,HC,2,O,4,H,2,C,2,O,4,酸效应,络合效应共存,K,sp,10,-9.7,pH=4.0,，,C,2,O,4,=0.2molL,-1,Y=0.01molL,-1,C,2,O,4,(H),10,0.3,Y(H),10,8.6,Y=Y/,Y(H),=10,-10.6,mol L,-1,Pb(Y),1+10,-10.6+18.0,10,7.4,K,sp,=,K,sp,Pb(Y),C,2,O,4,(H),=10,-9.7,+7.4+0.3,=10,-2.0,在此条件下，,PbC,2,O,4,不沉淀,Ca(Y),=1+10,-10.6+10.7,=,10,0.4,K,sp,=,K,sp,Ca(Y),C,2,O,4,(H),=10,-7.8+,0.4+0.3,10,-7.1,此时，,CaC,2,O,4,沉淀否？,Ca,2,沉淀完全，则,Pb,2,，,Ca,2,可分离。,(5).,影响,s,的其他因素,温度,:,t,，,s,溶解热不同,影响不同,.,室温过滤可减少损失,.,溶剂,:,相似者相溶,加入有机溶剂，,s,颗粒大小,:,小颗粒溶解度大,需陈化,.,形成胶束：,s,沉淀析出时形态：,2.,沉淀滴定,Precipitation Titration,沉淀反应为基础的分析方法,沉淀反应很多，但能用于沉淀滴定的不多，应用较多的是生成难溶,Ag,盐的反应,Ag,+,+Cl,-,=AgCl,Ag,+,+Br,-,=AgBr,Ag,+,+SCN,-,=AgSCN,银量法，,Cl,-,Br,-,I,-,CN,-,SCN,-,Ag,+,argentometric titrations,Precipitation Titration Curve,EXAMPLE:,Sketch a curve for the titration of 20.00 mL of 0.1000 M NaCl with 0.1000 M AgNO,3,.,titration curve=pAg vs.vol.AgNO,3,added,Ag,+,+X,-,=AgX K,sp,=Ag,+,X,+,pAg+pX=pK,sp,SP,pCl=pAg=1/2 pKsp=4.91,+0.1%,Ag,+,=5.0,10,-5,mol/L,pAg=4.30,pCl=pKsp-pAg=9.81-4.30=5.51,-0.1%,Cl,-,=5.0,10,-5,mol/L,pCl=4.30,pAg=pKsp-pCl=9.81-4.30=5.51,Initial point,Cl,-,=0.1000 mol/L,pCl=1.00,Taking account of the,dissolution of the precipitation,-0.1%,Cl,-,=Cl,-,sur,+Cl,-,sol,Cl,-,sol,=Ag,+,=a,Ksp=Cl,-,Ag,+,=(Cl,-,sur,+a)a,a=2.9,10,-6,mol/L,pCl=4.28,pAg=pKsp-pCl=9.81-4.28=5.53,AgNO,3,NaCl,(I,-,),0 50 100 150 200,T,%,pAg,0.1mol/L,0.1mol/L,1mol/L,1mol/L,4.9,6.5,3.3,5.5,4.3,0,2,4,6,8,10,AgI,pAg Jump,increase by,2,when the,concentration,increase,10,fold.,pAg Jump,increase by,n,when the,Ksp,dcrease,10,n,End-Point Detection,argentometric titrations,（银量法）,a.Mohr,(potassuim chromate as indicator),titration of Cl,-,with AgNO,3,Titration reaction:Ag,+,+Cl,-,AgCl,(,s,)white,Indication reaction:Ag,+,+CrO,4,2-,Ag,2,CrO,4,(,s,)brick red,Something Notable:,Indicator dosage,Acidity of solutions,interferences,Experimental dosage,：,5.2-2.6,10,-3,mol/L,Indicator dosage:,sp,Ag,+,=Cl,-,=K,sp(AgCl),1/2,=1.25,10,-5,mol/L,CrO,4,2-,=K,sp(Ag2CrO4),/Ag,+,2,=,0.7010,-2,mol/L,用,0.1000mol/L Ag,+,滴定,0.1000mol/LKCl,指示剂,CrO,4,2-,=5.0010,-3,mol/L,。计算由指示剂引入的终点误差。,(,生成可判断终点的,AgCrO,4,需消耗,2.0010,-5,mol/L,的,Ag,+,),sp,时,Ag,+,sp,=Cl,-,sp,=K,sp(AgCl),1/2,=1.25,10,-5,mol/L,CrO,4,2-,Ag,+,2,=K,sp(Ag2CrO4),出现沉淀时,:,Ag,+,=K,sp(Ag2CrO4),/CrO,4,2-,1/2,=,1.4810,-5,mol/L,明显,Ag,+,过量了,此时,Cl,-,=K,sp,/Ag,+,=1.0510,-5,mol/L,Ag,+,过量,=Ag,+,-Cl,-,=1.4810,-5,-1.0510,-5,=0.4310,-5,总多消耗的,Ag,+,:,Ag,+,总,=0.4310,-5,+2.0010,-5,=2.4310,-5,mol/L,终点误差：,滴定剂过量的量,被测物的量,2.43,10,-5,2V,0.1000,V,100%,=,100%,=0.049%,Acidity of solutions,acidity,：,pH 6.5 10.5,；,pH 6.5 7.2 when NH,3,exist,s,trong acid,：,H,+,+CrO,4,Cr,2,O,7,2-,(,K,=4.310,14,),Strong base,：,Ag,2,O precipitation,Advantage,：,direct,simple,accurate for measurement of Cl,-,and Br,-,Disadvantage:,interferences,(precipitation of Ag,m,A,n,、,M,m,(CrO,4,),n,、,M,(OH),n,）,;,I,-,、,SCN,-,can not be detected since I-and SCN are strongly adsorbed on the surface of the precipitates,；,b.Volhard,(NH,4,Fe(SO,4,),2,as indicator),i).Direct titration(determining Ag,+,),Titration reaction:Ag,+,+SCN,-,AgSCN,(,s,)white,Indication reaction:Fe,3+,+SCN,-,FeSCN,2+,(,s,),red,Something Notable:,Acidity of solutions,(,0.3 mol/L HNO,3,),Concentration of indicator(,1-2 ml 40%),Interference of adsorption,b.Volhard,ii).Back titration(for determination of haloid ions),Error occurs due to the reaction:,SCN,-,+Fe,3+,AgSCN,AgCl Ag,+,+Cl,-,+,FeSCN,2+,K,sp,(AgSCN),K,sp,(AgCl),(2.0,10,-12,)(3.2,10,-10,),Ways to avoid the error:,c.Fajans-titration of Cl,-,with AgNO,3,-,absorption indicator,dye absorbs on to the surface of the particles of AgCl,attracted by excess Cl,-,absorbed on the surface of the precipitate,Fajans,法常用吸附指示剂,指示剂,p,K,a,测定对象,滴定剂,颜色变化,滴定条件,(pH),荧光黄,7,Cl,-,Br,-,I,-,Ag,+,黄绿,粉红,7,10,二氯,荧光黄,4,Cl,-,Br,-,I,-,Ag,+,黄绿,粉红,4,10,曙红,2,Br,-,I,-,SCN,-,Ag,+,粉红,红紫,2,10,甲基紫,Ag,+,Cl,-,红,紫,酸性,沉淀对卤离子及指示剂的吸附能力：,Step titration,标准溶液的配制与标定,AgNO,3,:,（棕色瓶中保存）,纯品直接配制,(,贵,）,粗配后用,NaCl,标液标定其浓度,NH,4,SCN,:,以,AgNO,3,标液,Volhard,法标定,NaCl,工作基准或优级纯，直接配制,高温电炉中于,550,C,干燥,2h.,置于瓷坩埚中，在石棉网上用天然气灯加热,.,indicator,K,2,CrO,4,FeNH,4,(SO,4,),2,absorption indicator,titrant,Ag,SCN,-,Cl,-,or Ag,+,Titration reaction,Ag,+,+Cl,-,=AgCl,SCN,-,+Ag,+,=AgSCN,Ag,+,+Cl,-,=AgCl,Indication reaction,2Ag,+,+CrO,4,-,=,Ag,2,CrO,4,(,brick red,),Fe,3+,+SCN,-,=,FeSCN,2+,(red,),Structure change resulted from the indicator adsorption,pH,pH,6.510.5,0.3mol/L HNO,3,Depend on pKa of indicator,analytes,Cl,-,Br,-,CN,-,Ag,+,Ag,+,Cl,-,Br,-,I,-,SCN,-,et.al,Cl,-,Br,-,SCN,-,Ag,+,et.al,End point detection of precipitation titration by scanometry method without using indicator,Anal.Methods,2012,4,923-932,3.,重量分析法,Gravimetric Analysis,1 Overview of Gravimetry,1)Characters,Measuring,Mass,or change in Mass,Most,fundamental,of all analytical measurements,The,Oldest,analytical technique,2)Types of Gravimetric Methods,a.,Precipitation gravimetry,b.Electrogravimetry,c.Volatilization gravimetry,Why Gravimetry is Important?,Overview,cont.,1)Basis,2.Precipitation Gravimetry,precipitant,Precipitate,Analyte(in solution),Filtration,Quantifiable,form,Mass,rinsing,drying,metage,2)Attributes of Precipitate,a.Low Solubility,b.Easy to separate,c.High Purity,d.Easy to Form QF,2.Precipitation Gravimetry,cont.,3)Attributes of QF,a.Known composition,b.High stability,c.High molecular weight,2.Precipitation Gravimetry,cont.,Representative Gravimetric Analysis,Representative Gravimetric Analysis,cont.,4)Styles and formation of precipitate,Crystalloid precipitate (,晶形,0.1-1,m,CaC,2,O,4,BaSO,4,);,Curdy precipitate(,凝乳状,0.02-0.1m,AgCl);,Amorphous precipitate(,胶状沉淀,0.02 m,Fe(OH),3,),In precipitation gravimetry,we are wishing to get,Crystalloid,precipitate,2.Precipitation Gravimetry,cont.,Controlling particle size(of crystalloid),:,Nucleation,:,homogeneous&heterogeneous,inoculating crystal,（,晶种,）,critical,c,Q,/s,Growth:,Relative Supersaturation:,（相对过饱和度）,RSS=(c,Q,-s)/s,2.Precipitation Gravimetry,cont.,formation of precipitate,2.Precipitation Gravimetry,cont.,ion,nucleation,crystal nucleus,growth,particles,coacervation,Amorphous precipitate,directionalism,Crystalloid precipitate,Ways to form precipitates,Von Weimarn formular,Initial speed,Relative Supersaturation,S,:,solubility,Q,：,total concentration,Q S,:s,upersaturation,K,：,constant,聚集速度,(,分散度,),BaSO,4,1.110,-10,big 1000,Crystalloid,AgCl 1.810,-10,big 5.5,Curdy,CaC,2,O,4,H,2,O 2.310,-9,31,PbSO,4,1.710,-8,28,critical,both,Precipitate,K,sp,S,crystal nucleus,5)Factors affecting purity of precipitation,Co-precipitation(,共沉淀,),adsorption,mixed crystal,inclusion&occlusion,Post-,precipitation,（后沉淀）,Difference between the above two,Ways to minimize the impurity,2.Precipitation Gravimetry,cont.,Ba,2+,Cl,-,Ba,2+,Ba,2+,Ba,2+,Ba,2+,Ba,2+,Ba,2+,Ca,2+,Ca,2+,Cl,-,Cl,-,K,+,Na,+,Adsorption layer,Diffusion layer,Adsorption,后沉淀,主沉淀形成后，“诱导”杂质随后沉淀下来,缩短沉淀与母液共置的时间,吸附共沉淀（服从吸附规则）,是胶体沉淀不纯的主要原因，,洗涤,包藏共沉淀,是晶形沉淀不纯的主要原因，,陈化或重结晶,混晶共沉淀,预先将杂质分离除去,沉淀沾污对分析结果的影响（例,BaSO,4,法,）,吸附物质 测,SO,4,2-,测,Ba,2+,BaCl,2,（,+,）（,-,）,Na,2,SO,4,（,-,）（,+,）,Ways to minimize the impurity,1,）选择适当分析步骤,测少量组分含量时，首先沉淀含量少的组分,2,）改变易被吸附杂质的存在形式，降低其浓度,分离除去，或掩蔽。如将,Fe,3+,还原成,Fe,2+,3,）选择合适的沉淀剂,选用有机沉淀剂可有效减少共沉淀,4,）改善沉淀条件,温度，浓度，试剂加入次序或速度，是否陈化,5,）再沉淀,有效减小吸留或包埋的共沉淀及后沉淀现象,6)Optimization of precipitating conditions,For Crystalloid precipitate:,diluted,stir,temperature,aging(digestion),For Amorphous precipitate:,Concentration,temperature,addition of electrolyte,no aging,homogenous precipitation,2.Precipitation Gravimetry,cont.,1.,晶形沉淀,稀、热、慢、搅、陈,稀溶液中进行,:,Q,搅拌下滴加沉淀剂,:,防止局部过浓，,Q,热溶液中进行,:,s,陈化,:,得到大、完整晶体,冷滤,用构晶离子溶液洗涤,:,s,减小溶解损失,n=,K,Q,-s,s,无定形沉淀,浓溶液中进行,热溶液中进行,加入大量电解质,不必陈化，趁热过滤,用稀、热电解质溶液洗涤,减少水化程度，减少沉淀含水量，沉淀凝聚，防止形成胶体,Ca,2+,+(NH,4,),2,C,2,O,4,CaC,2,O,4,small precipitate,neutral,Weak basic,Ca,2+,+(NH,4,),2,C,2,O,4,CaC,2,O,4,S increases,H,+,acid effect,CO(NH,2,),2,+H,2,O CO,2,+2NH,3,90,0,C,hydrolyzation,H,2,C,2,O,4,HC,2,O,4,-,+H,+,，,pH,HC,2,O,4,-,C,2,O,4,2-,+H,+,C,2,O,4,2-,，,RSS,Ca,2+,+C,2,O,4,2-,CaC,2,O,4,big,pure,dense precipitate,of,CaC,2,O,4,Homogenous Precipitation(,均匀沉淀,),the precipitating ion is not added to the solution but is generated throughout the solution by a,homogenous chemical reaction,.This is the ultimate in precipitation technique.Since the precipitating agent is,generated evenly throughout the solution,local excess of the precipitating agent are avoided.,In precipitation from homogenous solution the supersaturation,(Q-S)is kept extremely low at all times resulting in a very pure,dense precipitate.,草酸二酯,氨基磺酸,硫代乙酰胺,7)Organic precipitating agents,1.More kinds of agents could be used,2.,Higher selectivity,3.Lower solubility,4.Lower adsorption of inorganic ions,5.Bigger,Mw,MnO,4,-,HgCl,4,2-,螯合物,离子缔合物,铜铁试剂,水杨醛肟,硝酸灵,8)filtering,washing and drying,Filtering,Washing,Drying,Calculation,Thermogravimetric curve for calcium salicylate,