分析化学讲义8.pdf

例4100.2mol/L NaOH滴定4100.2mol/L HCl，是否可行，求突跃大小。若pHep=6，求TE。解：强碱滴定强酸生成水是生成反应型（与沉淀生成同），滴定可行性判据为622,10eqeqDDc。恰好满足精密滴定6272422,72110)10()101(100.1)(=+eqeqDWeqeqDcKOHH二、质子转移反应类型的滴定二、质子转移反应类型的滴定1.强酸（碱）的滴定突跃大小：5.010210001.0 2001.074,=eqeqDDcy21.0303.2)5.0(sinh303.2)(sinh11=ypH突跃0.42个pH单位：6.79-7.21%110)1010(10)1010(1764117,=eqDpHpHeqcDTEpH或)303.2sinh(2,pHcDTEeqDeq=347109.9)1(303.2sinh10102=例 0.02 mol/L HCl与 0.02 mol/L HAc混合液用0.02 mol/LNaOH滴定，能否滴定HCl和连续滴定HAc？解：滴定HCl，化学计量点为HAc和H2OH+=OH-+Ac-H+eq=Ac-eq421521,102.4)01.0108.1()(+=eqHAcaeqcKHHAc判别式4224222,22,101067.5)102.4(01.0=+=eqHAcbeqeqDcKDc计量点21,)(eqHAcbeqcKOH=72.521351410)107.6.108.110(=pH=8.28由此：滴定一元弱酸 8a6bHAbHA2HA1010=cKKcKcc或 滴定一元弱碱 8b6aBaB2B1010=cKKcKcc或 强酸+弱酸选择滴定 6aHA2H10HA+Kcc 强碱+弱碱选择滴定 6bB2OH10BKcc 注：注：c均为化学计量点时的分析浓度。例0.02 mol/L NaOH滴定含0.02 mol/L HAc和0.02mol/L NH4Cl的混合液，可否选择滴定，连续滴定？如能滴，随机误差多大？解：+4NHHAcaaKK，先滴HAc，化学计量点为Ac-和NH4+H+HAc=NH3+OH-近似HAceq=NH3eq相当于NH3+HAc=NH4+Ac-滴定反应+=+434NHHAcaatKKHHHAcNHAcNHK3.两种一元弱酸混合酸的滴定21aa421t4eq3eq4NHHAcAcNHAcNHNHHAc=+KKK 判别式 eq4aeqHAc,aaeqeq4a2eqHAc,2eq2eqHAc,NHAcNHHAc4NHHAcHAc4NH+=KcKKKcc 4410510102.301.0106.501.0108.1=可满足工业分析要求 求H+eq：00.7pH100.101.0106.5108.1AcHAcH106.501.001.0108.1106.5HAc755eqeqaeq521510eq=+K eqHAc,pHpHeq)1010(DTEc=2.0pH=35eqHAc,eq2.02.05105)2.0303.2sinh(01.0106.52)pH303.2sinh(2DTE%5.0005.001.0)1010(106.5TE=c或 第二eq：NH3，Ac-和H2OH+HAc+NH4+=OH-简化21,4)(43eqNHbeqeqcKOHNHNH+=+4215105.3)302.0108.1(=判别式42242242,10107.3)105.3(0067.04=2.01020202a1 H+不能忽略 H+H3PO4=HPO42-相当于弱碱 HPO42-滴定 H3PO4至 H2PO4-HPO42-+H3PO4=2H2PO4-1.11.01011POH1POHH1POHPOHHHPOHPOHPOHHPOHPOHHPOPOH242a434343POHaa244243424324242t14321=+=+=+=+=+KKKK 判别式 工业分析4472aPOHaaatt2eq,POH2eq,POH2eq2eq,POH21t2eq,POH21t242eq24eq43eq10100.71.1103.1101DPOHHPOPOHD24312143434343=KKKKKKcccKcK 5212722142a42aaeq104.31.01011.0103.1101POHPOHH121+=+=+=KKK H2PO4-HPO42-+H+%36.0106.3)100.7(95.0)(1010)1010(DTE47.4pH104.3100.71.01.0103.1HPOPOHH321421t2.02.0eq,POHpHpHeq5214272442a432=+KcKm 第二 eq：H+H2PO4-+2H3PO4=PO43-+OH-简化 H2PO4-=PO43-+OH-看成 PO43-+H2PO4-=2HPO42-21t2POHeq34eq42eq324b343434POaat4213432POPOHD08.13/2.01051HPO1POOH1POOHPO=+=+=+=+=KcKKKK 判别式 4127aaaat2eq2eq,POH100.608.1102103.1D323242=KKKKKc 工业分析()321421t2.02.01047eq24eq42aeq4214221t2eq,POHeq42109.3)100.6(95.0)(1010TE28.9pH103.53/2.0107.2103.1HPOPOHH107.2100.63/2.0POH242+=KKKc 若计算两步合并滴定的误差则减半，即2103 第三 eq：H+HPO42-+2H2PO4-+3H3PO4=OH-简化HPO42-eq=OH-eq强碱滴定一元弱酸101312,101010242.0324=KcKc 工业分析()89.3pH1029.131.0105HHCOHDeq421721eq,HCOaeqeq3eqeq31=+cK()()3429.029.0,3106.53/1.01029.11010101029.089.36.33=eqHCOeqpHpHcHCOTEpH当由Na2CO3直接滴至H2CO3时，其滴定误差减半，为0.3%.用Na2CO3标定HCl时，通常在终点前加热除去CO2。若剩余1%，即4103.3mol/L，则9.443.610103.310+=H随机误差()42.02.09.41021010033.0210=TE滴定时以甲基红、溴甲酚绿作指示剂为宜。5.强碱与弱碱混合碱的滴定强碱与弱碱混合碱的滴定)10(10)10(10)10(10108246214612cKKKcKcbbbBbOH例0.1 mol/L HCl滴定0.1 mol/L NaOH和0.1 mol/LNa2CO3混合物，能滴哪步，随机终点误差多大？解：滴定NaOH判据4211142,2,101041081005.005.0132=beqCONaeqNaOHKcc不能选择滴定NaOH，可合并滴定NaOH和Na2CO3的第一步第一 eq：H+eq=8.2 321321aa2.02.034eq,CONaeqNaOH,2.02.0eq421321aaeq,CONaeq100.6)102.6(295.0)/(21010TE 100.6033.0033.095.0102.4)1010(DTE102.4)102.6(3/1.0)/(D21322132=+=+=KKccKKc或m第二 eq：与上例相同 ()()3217eq,HCO21a2.02.0102.41054/1.095.01010TE31=ccKm