第3章+化学平衡在滴定分析法中的应用.doc

第三章 化学平衡在滴定分析法中的应用 10第三章 化学平衡在滴定分析法中的应用这章可以说是本书的重头戏。刚一接触可能会一头雾水，但多看几遍，无非就是两三个内容：林邦误差公式、滴定可行性判据、条件电位。其中，可行性判据很有用，建议熟记；化学计量点的有关问题也要注意；再有滴定突跃、滴定误差。考试无非出四大滴定的计算，酸碱滴定很可能考混酸（书后2430多题那种），熟记这个判据；沉淀滴定主要就是考察Ksp了，与无机会有联系；滴到某一点时的E求法要掌握（书上有例子），虽然只考最基础的。本章公式很多，而本课程学习时间有限，因此公式推导过程一般了解即可；多元酸的滴定通常情况下不要求，只需了解判据；电子转移类的，非对称型不作要求，对称型也不要求误差。（以上是小化情况，大化也许稍有不同）书后部分习题解析( for reference )1. 10.00mL = 0.5 Cu2+ = 0.02(1- 0.5)/(1+0.5)= 10-2.18 pCu = 2.1819.98mL = 0.999 Cu2+ = 10-5.00 pCu = 5.0020.00mL = 1Cu + Y = CuY lg= lg- lgY(H) = 18.80 - 8.44 = 10.36KCuY =CuYeq/(CuY) Cu=(C Cueq/ KCuY)1/2 =(0.01/10-10.36 )1/2 = 10-6.18 pCueq = 6.18 20.02mL =1.001 Y = 0.02(1.001- 1)/(1+1.001)= 10-5.00 Cu= C CuY/(Y)= 0.01/1010.36 - 5.00 = 10-7.36 pCu = 7.36 20.20mL =1.01 Y= 0.02(1.01- 1)/(1+1.01)= 10-4.00 Cu= C CuY/(Y)= 0.01/1010.36 - 4.00 = 10-8.36 pCu = 8.362. = 0.5 Mg= 0.01(1- 0.5)/(1+ 0.5)= 10-2.48 = 0.95 Mg= 0.01(1- 0.95)/(1+ 0.95)= 10-3.59 = 0.99 Mg= 0.01(1- 0.99)/(1+ 0.99)= 10-4.30 = 0.998 Mg= 0.01(1- 0.998)/(1+ 0.998)= 10-5.00 = 1.00 Mg= 10-5.28 = 1.002 Mg= 10-5.55 = 1.01 Mg= 10-6.25 3. = 0.5 I= C(1- 0.5)/(1+0.5)= 10-0.48 Ag= Ksp/I= 10-16.03/10-0.48 = 10-14.55 pAg = 14.55 = 0.999 I= C(1- 0.999)/(1+ 0.999)= 10-4.30 Ag= Ksp/I= 10-16.03/10-4.30 = 10-11.73 pAg = 11.73 = 1 Ag = I = (Ksp)1/2 = 10-8.02 pAg = 8.02 = 1.001 pAg = 4.30pAg = 6.00 pAg = pAgeqpAgep = 6.008.02 = -2.02TE = Ag(10-pAg10pAg )/C = 0.002 %4. eq : AgCl= Ksp Ageq = (Ksp)1/2 = (10-9.75 )1/2 = 10-4.875 pAg = pAgeq pAgep = 4.8754.699 = 0.176 TE = Ag(10-pAg10pAg )/C = 0.0067 %5. Ksp(AgCl) = 10-9.75 Ksp(AgI) = 10-16.03 第一计量点： Ag = I 0.0850 = 0.2V V = 20mL Ieq = (Ksp)1/2 = (10-16.03 )1/2 = 10-8.01 I/C2 = 10-8.01 /(0.0850/70) = 10-4.68 %6. NH3= CNH30 = CNH3/2Ka/(Ka + H)= 10-1.75 Cu(NH3) = 1+1NH3+5NH35 = 106.43 lgCu(OH) = 0.8 Cu =Cu(NH3) +Cu(OH)1 = 106.43 lgY(H) = 1.28 lgK= 11.09 pCueq = 0.5(11.09 + 2)= 6.54 ; pCuep = 12.8 - 6.43 = 6.37 pCu = 6.376.54 = -0.17 TE = -0.002 %7. Zn + Y = ZnY H = KaHAc/Ac= 10-5.09 Y(H) = 106.45 ; Y(Mg) = 1 + Mg= 106.70 Y = 106.45 + 106.701 = 106.87 lgKZnY= 16.56.89 = 9.61 ; pZneq = 0.5(9.61 + 2)= 5.80 pZn = 4.805.80 = -1.0 TE = (10-1.0 - 101.0 )/(109.612 )2 = -10-2.8 = -0.16 %8. -0.006 %9. Cu + Y = CuY OH NH3 H Ag Cu(OH) Cu(NH3) Y(H) Y(Ag) NH3 Ag(NH3) NH3= Cep0 = 0.4/2Ka/(Ka + H) = 0.210-9.37/(10-10 + 10-9.37 ) = 0.162 mol/L = 10-0.79 mol/LAg(NH3) = 1 + 1NH3 + 2NH32 = 105.47 Ageq = Cep/Ag(NH3) = 0.50.02/105.47 = 10-7.47 mol/LY(Ag) = 1 + KAgYAg = 1 + 107.32-7.47 = 100.23 Y总 = Y(H) + Y(Ag)1 = 100.45 + 100.231 = 100.55 Cu(NH3) = 1 + 1NH3 + 5NH35 = 1010.30 Cu总 = Cu(OH) + Cu(NH3) - 1 = 101.7 + 1010.301 = 1010.30 lgKCuY= lgKCuY - lgCu总 - lgY总 = 18.8010.30.55 = 7.95KCuY= 107.95 TE = (10 pCu10 - pCu)/( KCuYCep)1/2 0.2 %|y| = 0.002Cep/(2Cueq) = 0.002(107.95 0.01)1/2/2 = 0.944pCu = lgy + (y + 1) = 0.3710. 0.016 %11. 理论上可分步滴定，但无指示剂12.(1) lgKCuY = 18.80 ; lgKBaY = 7.86 (差6，可以滴定) lgY(H) = lgKCuY8 = 10.8 查得 pH = 2.9 (最高酸度) 最低酸度 OH= (Ksp/CCu)1/2 = (10-19.66/CCu)1/2 = 10-8.98 mol/L pH = 148.98 = 5.02 当Y(H) = Y(Ba) Y(Ba) = 1 + KBaYBa = 105.86 查得 pH = 5.3 5.02 2.95.02 (2) 最高：lgY(H) = lgK8 = 25.18 = 17.1 查得 pH = 1.2 最低：Fe3+ 水解酸度 pH = 2.1 (代初始浓度) Fe3+ 掩蔽酸度: pH = 2.3 1.22.113.(1) 6.4 , 4.2 (2) 9.914. pM = 0.5 TE = 0.001 pH = 5.0 Y(H) = 106.45 TE = (10 pD10 - pD)/( KMYCep)1/2 = (100.5-10-0.5 )/(0.01KMY)1/2 = 0.001(注：用林邦公式算出来的是条件平衡常数，要换算成平衡常数)KMY= 108.91 lgK= lgK - lgY(H)lgK = 8.91 + 6.45 = 15.36 K = 1015.36 15. (pH值要根据质子条件式推出)(1) 参考水准：H2O和HPO42- H + H2PO4- + 2H3PO4 = OH + PO43- (2) 参考水准：H2O和en分子 H + H3+NCH2CH2NH2 + 2H3+NCH2CH2N+H3 = OH(3) 参考水准：H2O和HAc H - CHCl = OH + Ac- (4) 参考水准：H2O和C2O42- H + HC2O4- + 2H2C2O4 = OH - CNaOH(5) 参考水准：H2O和F- : H + (HF - CHF) = OH 或H2O和HF : H = OH + (F - CNaF) (6) 参考水准：H2O和NH2OH , CH3NH2 H + N+H3OH + CH3N+H3 = OH (7) 参考水准：H2O和HSO4- (H CH2SO4) + H2SO4 = OH + SO42- (8) 参考水准：H2O , NH4+ 和H2PO4- H + H3PO4 = OH + NH3 + HPO42- + 2PO43- 16.(1) 2.42 (2) 参考水准：H2O和NH4+ H = NH3 + OH Kb = 10-4.74 CNH4+ 20Kb 可以舍去OH H = NH3 = C0 = CKa/(Ka + H) C 400Ka 可以舍分母Ka Ka = Kw/Kb H = (CKa)1/2 = (0.210-9.26 )1/2 = 10-4.98 pH = 4.98 (3) 1.89 (4) C = 0.2/0.6 = 0.333 mol/L 参考水准：H2O , A H + H+A = OH H+A = OH OH = (CeqKb)1/2 H = (KwKa/C)1/2 = 10-9.38 pH = 9.38 (5) 1.317. (1) 2.81 (2) 3.31 (3) 4.4218.(1) 2.45 (2) 3.35 (3) 混合后生成一个缓冲体系 CHNO2 = 0.0620/50 = 0.024 mol/L CNaNO2 = 0.0430/50 = 0.024 mol/L 参考水准1：HNO2和H2O H = OH + (NO2- CNaNO2) 参考水准2：NO2- 和H2O H + HNO2 - CHNO2 = OH NO2- = CNaNO2 - OH + H HNO2 = CHNO2 + OHH Ka = HNO2- / HNO2 H = KaHNO2/ NO2- = Ka(CHNO2 +OH-H)/(CNaNO2OH+H) (C 20Ka , C 20Kb) pH = 3.29 (4) 1.6119.(1) 4.44 (2) 4.44 (3) 1.0320.(1) 10-1.81 (2) 参考水准：H2O和H2PO4- H + H3PO4 = OH + HPO42- + 2PO43- H + H3PO4 = HPO42- H3PO4 = HH2PO4- /Ka1 HPO42- = Ka2H2PO4- /H H + HH2PO4- /Ka1 = Ka2H2PO4- /H H2 (Ka1 + C)/Ka1 = Ka2C H = Ka1Ka1C/(Ka1 + C)1/2 = 2.010-5 mol/L pH = 4.70 (3) 参考水准：H2O和HPO42- H + H2PO4- + 2H3PO4 = OH + PO43- H2PO4- = OH + PO43- H2PO4- = HHPO42- /Ka2 PO43- = HPO42- Ka3/H HHPO42- /Ka2 = Kw/H + HPO42- Ka3/H H = Ka2(Kw + Ka3C)/C1/2 = 10-9.68 pH = 9.68(4) 10-12.07 21.(1) 2.30 (2) 2.3222.(1) 用缓冲溶液直接计算较简单（书P80） pH = pKa + lgA/HA H3PO4 = 0.05(50 - 25)/(50 + 25) = 0.0167 mol/L H2PO4- = 0.0525/75 = 0.0167 mol/L pH = pKa1 = 2.12 (2) 4.52 (3) 6.9023.(1) 4.02 (2) 9.17424.【较典型】 产物是NaCOOH 以COOH - 和H2O为参考水准H + HCOOH = OHHCOOH = OHHCOOH: pKa = 3.74 ; pKb = 10.26OH = (KbCep)1/2 = 10-5.78 ( Cep为平衡浓度，是原始C的1/2 ) pH = 145.78 = 8.22y = 0.001Cep/(2D) = 0.0010.05/(210-5.78 ) = 101.18 |pH| = lgy +(y + 1) = 1.48 (突跃)前0.1 % pH前 = 8.221.48 = 6.74后0.1 % pH后 = 8.22 + 1.48 = 9.70pH = 7.0 pH = 7.08.22 = -1.22TE = D(10 pD10 - pD)/CHCOOH,ep = 10-5.78(10-1.22-101.22 )/0.05 = -0.05 %pH = 10 pH = 108.22 = 1.78 TE = 0.20 %25.(1) 8.4 (2) -0.8 % (3) 0.08347 %26. 69 %27. 3.75 ; 3.69 ; 3.8128. 1.6 %29. （用强酸滴定强碱肯定能准确滴定）先判断能否分别滴定：C2NaOH/(KbCNaAc) 106 能KbCNaAc 10-8 不能准确滴定NaAc , 只能准确滴定NaOHAc , H2O为参考水准OH = (KbC)1/2 = (10-9.26 0.1)1/2 = 10-5.13 ; pH = 145.13 = 8.87pDeq = pOHeq =(14 - 9)- 5.13 = 0.13TE = D(10 pD10 - pD)/Cep = 10-5.13(10-0.13-100.13 )/0.01 = -0.0045 %30. pKa1 = 2.95 , pKa2 = 5.41判断：Ka1/Ka2 10-8 能准确滴定参考水准：A2- , H2OOH = (KbCep)1/2 = (10-8.59 0.05/2)1/2 = 10-5.10 pH = 145.10 = 8.90 ; pH = 7.68.9 = -1.3TE = 0.5D(10-1.3 - 101.3 )/Cep = 10-5.10(10-1.3 - 101.3 )/0.025 = -0.32 %(滴2个H ，则TE需除以2)31. 5.28 ； 6.26 ； 4.3032. 3.13 ； 8.9033. 0.04 %34. CHCl/(CNH4+Ka) 106 可以分别滴定（多元酸叫分步滴定）CNH4+Ka 10-8 能准确滴定(2) 【碱】 CKb 10-8 不能准确滴定(3) 【酸】 CKa 10-8 不能准确滴定(4) 【碱】 CKb1 10-8 不能准确滴定36.(1) 2级 Ka1/Ka2 10-8 可以一步滴定合量 (2) 3个 Ka1/Ka2 10-8 不能分步,可以一步合量 (3) CHCl/(C丙酸Ka) 10-8 不能分步,可以一步合量滴定 (4) Ka1/Ka硼 104 可以分步滴定 ;KaAcC 10-8 可精确滴定醋酸 ; Ka硼C 10-8 不能精确滴定硼酸37. Sn4+ + 2e = Sn2+ VO2+ (V) + 2H+ + e = VO2+ (IV) + H2O加入5 mL E = ESn4+/Sn2+ + 0.059/2lgSn4+ /Sn2+ = 0.14 + 0.059/2lg(5/15) = 0.13 V加入19.98 mL E = 0.14 + 0.059/2lg(19.98/0.02) = 0.23 V加入20.