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1、 第四章 滴定分析法的应用 6第四章 滴定分析法的应用 本章与其他章节的结合性很强。主要三个内容：指示剂、标准溶液、应用实例。需要记住常用的指示剂：酚酞、甲基橙、甲基红、溴百里酚蓝；铬黑T（碱性体系使用）、吡啶偶氮萘酚、二甲酚橙，等等，不过考试不会在这方面难为人。影响指示剂变色的因素可能会有选择、填空题；应用中，银量法比较重要，注意总结几种方法间的区别联系、各自的适用条件和范围；还会有设计分析方法的内容。 书后部分习题解析 ( for reference )1.(1) eq: OH = (KbC)1/2 = (10-9.26 0.1)1/2 = 10-5.13 pH = 8.87 选P.P (
2、2) H = (KaC)1/2 = (10-9.26 0.1)1/2 = 10-5.13 pH = 5.13 选M.R (3) H = Ka2(Ka3C + Kw)/C1/2 = 10-9.7 选百里酚酞 (4) pKb = 8.85 OH = (KbC)1/2 = (10-8.85 0.1)1/2 = 10-4.92 pH = 9.08 选P.P (5) 选X.O 在pH = 1.0 (6) 选X.O 在pH = 5.0 ; 或EBT , pH = 10 (NH3-NH4+ 缓冲) (7) Cu-PAN (8) pH = 12.6 选GBHA (NaOH-硼砂缓冲)2.(1) 终点pH =
3、7.0 y = 0.0010.0010.5/(210-7 )= 5突跃|pH| = lgy +(y + 1)1/2 = 0.726.287.72 选溴百里酚蓝(B.B) (2) (选指示剂的原则：1、终点接近；2、在突跃范围内)NH2OH , H2O 质子条件式：H + NH3+OH = OH (C 20Ka) NH3+OH = OH OH = (KbC)1/2 = 10-4.76 (书P147判据) pH = 144.76 = 9.24 y = 0.0010.05/(210-4.76 )= 1.44 |pH| = lgy +(y + 1)1/2 = 0.50 pH = 9.240.50 8.
4、749.74 选酚酞(P.P) (3) H2AsO4- , H2O H + H3AsO4 = OH + HAsO42- + 2AsO43- pKa1 = 2.2 , pKa2 = 7.0 C(0.052/3) 20Kb2 H + H3AsO4 = HAsO42- H + CH/Ka1 = Ka2C/H H = Ka1Ka2C/(Ka1 + C)1/2 = 10-4.64 pH = 4.64 y = 0.001(0.05/3)/(210-4.64 )= 0.72 突跃 pH = lgy +(y + 1)1/2 = 0.29 pH: 4.640.29 4.354.93 选甲基红(M.R)或溴甲酚绿
5、(B.G) (4) NH2OH = 0.150/90 = 10-1.26 (VHCl = 500.08/0.1 = 40 mL) OH = (KbC)1/2 = (10-8.04 10-1.26 )1/2 = 10-4.65 pH = 9.35 选 P.P (5) CH2PO4- = 0.052/3 = 10-1.48 H=Ka1Ka2C/(Ka1 +C)1/2 = 10-4.71 pH = 4.71 选M.R或溴甲酚绿3.(1) M1 = 0.125105.99/(21000)= 0.1325 M2 = 0.120105.99/(21000)= 0.1060 称0.110.13 g (2)
6、M1 = 0.08025381.37/(21000)= 0.3814 M2 = 0.08025381.37/(21000)= 0.3051 称0.310.38 g (3) M1 = 0.1525126.07/(21000)= 0.2364 M2 = 0.1520126.07/(21000)= 0.1891 称0.190.20 g (4) M1 = 0.2025134/(21000)= 0.3350 M2 = 0.2020134/(21000)= 0.268 称0.270.34 g4.(1) pKa1 = 1.22 pKa2 = 4.19 Ka1/Ka2 10-8 不能分步，可滴合量 OH =
7、(Kb1C)1/2 = (10-9.810.1/3)1/2 = 10-5.64 pH = 8.36 选P.P (2) pKa1 = 3.04 pKa2 = 4.37 Ka1/Ka2 104 eq: H = Ka1Ka2C/(Ka1 + C)1/2 = 10-2.2 - 7.0 - 1.0/(102.2 + 10-1.0 )1/2 = 10-4.61 选M.O或M.R (4) pKa1 = 3.13 pKa2 = 4.76 pKa3 = 6.4 Ka3C 10-8 不能分步，一次滴三个H OH = (Kb1C)1/2 = (10-7.60.2/4)1/2 = 10-4.46 pH = 9.54
8、选P.P (5) pKa = 4.87 C2HCl/(KaC) = 0.12/(0.110-4.87 ) = 103.87 104 KaHAcC 10-8 可滴HAc HAceq = NH3eq H = (KaHAcKa硼NH4+ /Ac- )1/2 = (KaHAcKa硼)1/2 = (10-4.74 - 9.24 )1/2 = 10-6.99 选溴百里酚蓝5.(1) 用酸碱滴定测合量(选P.P) ，用银量法(佛尔哈德法)测Cl (2) 第一步，测HCl H = (KaC)1/2 10-5 选M.R 第二步，用甲醛法 选P.P (3) 第一步，测HAc 选溴百里酚蓝 第二步，用佛尔哈德法测C
9、l (4) 一份在pH = 5.0用EDTA滴定，测Zn2+ 选X.O ； 一份在pH = 10.0用EDTA滴定，测合量 选EBT (5) 在pH = 13.0(12.6)时用EDTA滴Ca2+ 选GBHA ；在pH = 10.0用EDTA滴定Mg2+ 选EBT (6) 氯乙酸-乙酸缓冲，pH = 2.0 用EDTA滴Fe3+ ，磺基水杨酸作指示剂 ； 然后调pH = 3.5 ，加过量EDTA，加热，用标准金属离子返滴定测Al3+ , PAN为指示剂。6.(1) CNaOH 偏低 (2) CHCl 偏高 (3) CEDTA 偏低 (4) CAgNO3 偏高7.(1) C2HCl/(Ka1CH
10、3PO4) = 0.12/(0.110-2.12 ) = 101.12 104 可以分别滴定，只能滴HAc H = (Ka HAcKa H3BO3)1/2 = (10-4.74 -9.24 )1/2 = 10-6.99 选溴百里酚蓝 (3) 可以分别滴定，可以滴H2SO4 H = (Ka HSO4Ka H3BO3)1/2 = (10-2.0 - 9.24 )1/2 = 10-5.62 选M.R (4) pKa 氯乙酸 = 2.86 Ka/Ka= 10-2.86/10-4.74 104 可以分别滴定，只能滴HCOOH H = (KaKa)1/2 = (10-5.41 -9.95 )1/2 = 1
11、0-7.68 选溴百里酚蓝或M.R (6) pKa HSO4 = 2.0 pKa2 = 7.20 Ka/Ka= 10-2.0/10-7.20 = 105.20 可以分别滴定 一eq: H = (KaKa2)1/2 = (10-2.0 -7.20 )1/2 = 10-4.6 选M.O 二eq: H = Ka2(Ka3C + Kw)/C1/2 = 10-7.26(10-12.360.1/3 + 10-14 )/(0.1/3)1/2 = 109.67 选百里酚蓝 (7) pKb1 = 1.64 C/KbC 104 可分别滴定 H = (10-9.26 -5.15 )1/2 = 10-7.20 选溴百里酚蓝 (9) p
