电导法测定弱电解质电离平衡常数及数据处理

电导法测定醋酸电离常数一、实验目的了解溶液电导、电导率和摩尔电导率的概念；测量电解质溶液的摩尔电导率，并计算弱电解质溶液的电离常数。二、实验原理电解质溶液是靠正、负离子的迁移来传递电流。而弱电解质溶液中，只有已电离部分才能承担传递电量的任务。在无限稀释的溶液中可以认为电解质已全部电离，此时溶液的摩尔电导率为人打而且可用离子极限摩尔电导率相加而得。一定浓度下的摩尔电导率人m与无限稀释的溶液中摩尔电导率人.是有差别的。这由两个因素造成，一是电解质溶液的不完全离解，二是离子间存在着相互作用力。所以，人m通常称为表观摩尔电导率。AJATCm=a(U++U)/(U++U8)若U+=U，，U+=U则Am/A"广式中a为电离度。AB型弱电解质在溶液中电离达到平衡时，电离平衡常数吗气起始浓度C。，电离度a有以下关系：ABA++B-干三起始浓度mol/L：C000平衡浓度mol/L：C0•(1-a)aCQaCQKce=[c(A+)/ce][c(B-)/ce]/[c(AB)/ce]=C0a2/(1-a)=C0Am2/[ceAm(Am-Am)]根据离子独立定律，A可以从离子的无限稀释的摩尔电导率计算出来。A可以从mm电导率的测定求得，然后求出K：。AmC0/ce=A8^/Am-AmKce通过AmC0/ce〜1/Am作图，由直线斜率=Am2Kce,可求出K,三、仪器与试剂DDS-11A(T)型电导率仪1台；恒温槽1套；0.1000mol/L醋酸溶液。四、实验步骤1.调整恒温槽温度为25°C±0.3°C。用洗净、烘干的义形管1支，加入20.00mL的0.1000mol/L醋酸溶液，测其电导率。用吸取醋酸的移液管从电导池中吸出10.00mL醋酸溶液弃去，用另一支移液管取10.00mL电导水注入电导池，混合均匀，温度恒定后，测其电导率，如此操作，共稀释4次。倒去醋酸溶液，洗净电导池，最后用电导水淋洗。注入20mL电导水，测其电导率。五、实验注意事项本实验配制溶液时，均需用电导水。温度对电导有较大影响，所以整个实验必须在同一温度下进行。每次用电导水稀释溶液时，需温度相同。因此可以预先把电导水装入锥形瓶，置于恒温槽中恒温。六、数据记录及处理第一次实验：实验温度:25.2°C，电导池常数K(l/A):0.94m-1，人m=390.72s.cm2/mol-1表1醋酸电离常数的测定c(HAC)mol.L-1电导率K/us.cm-1Ams.m2.mol-1电离度aK6cK1K2K3K平1.000X10-15.20x1025.20x1025.20x1025.20x1025.17x10-40.01421.78x10-55.000X10-23.75x1023.76x1023.74x1023.75x1027.44x10-40.01991.85x10-52.500X10-22.62x1022.66x1022.68x1022.65x1021.05x10-30.02751.85x10-51.250X10-31.86x1021.87x1021.88x1021.87x1021.47x10-20.03971.85x10-56.250X10-41.30x1021.29x1021.28x1021.29x1022.02x10-20.05451.76x10-5电导水2.902.892.912.904、均值)=L82x10-5计算：A--KACK电导水--={(KHAC-k费水)x10-7/c(HAC)}HAC电导水Am(1)={(0.520x103-2.90)/(1.000x10-1)}x10-7=5.17x10-4s・m2.mol-1Am(2)={(0.375x103-2.90)/(5.000x10-2)}x10-7=7.44x10-4s・m2.mol-1Am(3)={(0.265x103-2.90)/(2.500x10-2)}x10-7=1.05x10-3s・m2.mol-1Am(4)={(0.187x103-2.90)/(1.250x10-3)}x10-7=1.47x10-2s・m2.mol-1Am(5)={(0.129x103-2.90)/(6.250x10-4)}x10-7=2.02x10-2s・m2.mol-1AA+A2・2a=A/Aa(2)=7.44x10-4/3.9072x10-2=0.0199a(3)=1.05x10-3/3.9072x10-2=0.0275a(4)=1.47x10-2/3.9072x10-2=0.0397a(5)=2.02x10-2/3.9072x10-2=0.0545K(e=CQAm2/[人皿-人m)Kce(1)=1.000x10-1x(5.17x10-4)2/[390.72x(390.72-5.17)x10-8]=1.78x10-5Kce(2)=5.000x10-2x(7.44x10-4)2/[390.72x(390.72-7.44)x10-8]=1.85x10-5Kce(3)=2.500x10-2x(1.05x10-3)2/[390.72x(390.72-1.05)x10-8]=1.85x10-5Kc%4)=1.250x10-3x(1.47x10-3)2/[390.72x(390.72-1.47)x10-8]=1.85x10-5Kce(5)=6.250x10-3x(2.02x10-3)2/[390.72x(390.72-2.02)x10-8]=1.76x10-5K：(平均值)=1.82x10-5表2醋酸电离常数的测定mo0.000050.000040.000030.00002mo0.000050.000040.000030.000020.000014006008001000120014001600180020001/A/s.m2.mol-1mc(HAC)mol.L-1Ams・m2.mol-1"ms・m2.mol-11/AmmoLs-1.m-21.000X10-15.17x10-45.171x10-51.93x1035.000X10-27.44x10-43.721x10-51.34x1032.500X10-21.05x10-32.624x10-59.52x1021.250X10-31.47x10-31.841x10-56.8x1026.250X10-32.02x10-31.261x10-54.95x102直线斜率=2.721x10-8s2.m4.mol-2Ke=1.78x10-5第二次实验：实验温度:24.9°C,电导池常数WA):0.94m-i,人命=390.72s.cm2/mol-i表1醋酸电离常数的测定c(HAC)mol.L-1电导率K/us.cm-1Ams.m2.mol-1电离度aK6cK1K2K3K平1.000X10-15.22x1025.22x1025.22x1025.22x1025.19x10-40.01331.79x10-55.000X10-23.72x1023.73x1023.72x1023.72x1027.38x10-40.01891.82x10-52.500X10-22.65x1022.66x1022.68x1022.66x1021.05x10-30.02691.86x10-51.250X10-31.86x1021.84x1021.85x1021.85x1021.46x10-20.03721.80x10-56.250X10-41.32x1021.31x1021.30x1021.31x1022.05x10-20.05241.81x10-5电导水3.103.093.113.10K¥y=L82x10-5计算：Am/s-m2-mol-1=(KHAC-K电导水)us-cm-1x10-4/[c(HAC)mol-L-1x103]={(Khac-K电导水)x10-7/c(HAC)}Am(1)={(0.522x103-3.10)/(1.000x10-1)}x10-7=5.17x10-4s・m2.mol-1Am(2)={(0.372x103-3.10)/(5.000x10-2)}x10-7=7.44x10-4s・m2.mol-1Am(3)={(0.266x103-3.10)/(2.500x10-2)}x10-7=1.05x10-3s・m2.mol-1Am(4)={(0.185x103-3.10)/(1.250x10-3)}x10-7=1.46x10-2s・m2.mol-1Am(5)={(0.131x103-3.10)/(6.250x10-4)}x10-7=2.05x10-2s・m2.mol-1Am(HAC)=Am(H+)+Am(AC-)=349.82s.cm2.mol-1+40.9s・cm2.mol-1=390.72s.cm2/mol=3.9072x10-2s.m2.mol-1a=A/Aa(1)=5.19x10-4/3.9072x10-2=0.0133a(2)=7.38x10-4/3.9072x10-2=0.0189a(3)=1.05x10-3/3.9072x10-2=0.0269a(4)=1.46x10-2/3.9072x10-2=0.0372a(5)=2.05x10-2/3.9072x10-2=0.0524Kce=C0Am2/[Am(Am-Am)Kc*1)=1.000x10-1x(5.19x10-4)2/[390.72x(390.72-5.17)x10-8]=1.79x10-5Kce(2)=5.000x10-2x(7.38x10-4)2/[390.72x(390.72-7.44)x10-8]=1.82x10-5Kce(3)=2.500x10-2x(1.05x10-3)2/[390.72x(390.72-1.05)x10-8]=1.86x10-5Kce(4)=1.250x10-3x(1.46x10-3)2/[390.72x(390.72-1.47)x10-8]=1.80x10-5

X：(平均值)=1.82X10-5表2醋酸电离常数的测定实验温度:24.9°C,电导池常数K(l/A):0.94m-i,人m=390.72s.cm2/mol-ic(HAC)mol.L-1人ms・m2.mol-1C0即ms・m2.mol-11/人mmoLs-1.m-21.000X10-15.19x10-45.189x10-51.927x1035.000X10-27.38x10-43.686x10-51.355x1032.500X10-21.05x10-32.629x10-59.509x1021.250X10-31.46x10-21.819x10-56.872x1026.250X10-32.05x10-21.279x10-54.887x10