第五章+水溶液中的离子平衡3.ppt

. mol/L 的HAc水溶液(纯的弱酸溶液), Ka = ? 10-5C ? 400Ka HAc(aq) + H2O(l) H3O+(aq) + Ac-(aq)平衡: ?x x 10 10 (mol/L)? ??? ?????3 a[H O ] K C33[H O ] 10α100% 100% %C ???? ????电离度:在上述溶液中加入固体NaAc, mol/L1 HAc(aq) + H2O(l) H3O+(aq) + Ac-(aq)平衡: ?x ? x x+?[H O ] 10α100% 100% %C ???? ????电离度:??x = [H3O+] = ?10-5 mol/L因为Ac- 的同离子效应,使HAc 电离度大大下降!在NH3水溶液中加入NH4Cl:由于NH4+的同离子效应,使NH3电离度大大下降!同样,减少产物的浓度,酸碱的电离平衡右移,电离度增加。2在一个HA~ A-的体系中,总是满足这样的平衡关系:HA(aq) + H2O(l) H3O+(aq) + A-(aq) Ka / [H3O+] = [A-] / [HA]调节[H3O+] ,调节[A-]/[HA]比值调节[A- ]/[HA]比值,调节[H3O+] 3在一个HA ~ A-的体系中,电离平衡时: Ka / [H3O+] = [A- ] / [HA] fHA = [HA] / ([A- ] + [HA]) = fA- = [A- ] / ([A- ] + [HA]) =[][]HOHOKa33???Ka]O[HKa3??pH = 5时[HA]/[A-]=?P 3224在一个H2A 及其盐的体系中(P. 337): Ka1 Ka2 / [H3O+]2 = [A2- ] / [H2A]Ka1/[H3O+] = [HA-]/[H2A] Ka2 / [H3O+] = [A2-] / [HA-]在一个三元弱酸及其盐的体系中(P. 346)5例1: mol/L H2CO3在pH = 缓冲溶液中各离子的平衡浓度。已知H2CO3的Ka1 = ? 10-7Ka2 = ? 10-11pH = , [H3O+]= 10- = ?10-8 (mol/L)H2CO3(aq) + H2O(l) H3O+(aq) + HCO3- Ka1HCO3-(aq) + H2O(l) H3O+(aq) + CO32- Ka2物料平衡:C = [H2CO3] + [HCO3-] + [CO32-]6由Ka1 = [H3O+][HCO3-] / [H2CO3] 得: [H2CO3] = [H3O+] [HCO3-] / Ka1由Ka2 = [CO32-][H3O+] / [HCO3-] 得:[CO32-] = Ka2[HCO3-] / [H3O+]将[H2CO3],[CO32-]的表达式代入(3)得:a2 33 (mol/L)K [H O ]1[H O ] K???? ?? ?3[HCO ]7[CO32-] = Ka2[HCO3-] / [H3O+] = ?10-3 (mol/L)[H2CO3] = [H3O+][HCO3-] / Ka1 = ?10-3 (mol/L)[OH-] = Kw / [H3O+] = ?10-6 (mol/L)8?酸碱指示剂作用原理HIn + H2O H3O+ + In- 酸式碱式[In-] / [HIn] > 10 显碱色< ? [In-]