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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,3.4,酸碱缓冲溶液,生理缓冲溶液,人,体液,(37),正常,pH,为,7.35-7.45,。每人每天耗,O,2,600L,产生,CO,2,酸量约合,2,L,浓,HCl,除呼出,CO,2,及肾排酸外,归功于血液的缓冲作用。,血红蛋白,:,HHb,-,KHb,血浆蛋白,:,HPr,-,NaPr,氧络血红蛋白,:HHbO,2,-KHbO,2,磷酸盐,:H,2,PO,4,-,-HPO,4,2-,碳酸盐,:,H,2,CO,3,-HCO,3,-,(1.35mmolL,-1,27,mmol,L,-1,),pH=6.10+lg20=7.40,1,3.4.1,缓冲容量,(,p87),1,L,溶液中引入强碱或强酸的,mol,数与,pH,变化量的比值。,2,-,pH,曲线,(,p88),1 3 5 7 9 11 13,pH,2.88 4.76 8.88,p,K,a,10,8,6,4,2,0,10,2,H,+,HAc,+Ac,-,OH,-,0.1molL,-1,HAc,Ac,-,0.1,molL,-1,强酸,:,H+,=2.3H,+,2.3,c,(,HCl,)(pH11),共轭体系,:,HA A,-,HA A,-,=2.3,c,x,1,x,0,3,共轭体系缓冲容量的特点：,（,1,）,c,c,增大,增大,（,2,）,H,+,=,K,a,(pH=,p,K,a,),时,max,=0.575,c,（,3,）,缓冲范围,:,p,K,a,-1 pH,p,K,a,+1,p,K,a,-1,x,1,=0.9,x,0,=0.1,=0.36,max,p,K,a,+1,x,1,=0.1,x,0,=0.9,=0.36,max,p,K,a,2,0.99,0.01,=0.04,max,4,3.4.2,缓冲溶液的选择,1.,有较大的缓冲能力,:,c,较大,(,0.01,1,molL,-1,);,pH,p,K,a,即,c,a,c,b,11,4.5,6,8,10,HAc,NaAc,:,p,K,a,=4.76 (pH,4,5.5,),NH,4,OHNH,3,:,p,K,b,=4.75 (pH ),(CH,2,),6,N,4,(CH,2,),6,N,4,H,+,:,p,K,b,=8.87,(pH,),2.,不干扰测定,(,EDTA,滴定,Pb,2+,不用,HAc,-Ac,-,),。,5,常用缓冲溶液,(,p89),缓冲溶液,p,K,a,缓冲范围,氨基乙酸,+,HCl,2.35,1.5,3.0,氯乙酸,+,NaOH,2.86,2,3.5,甲酸,+,NaOH,3.77,3,4.5,HAc,+,NaAc,4.76,4,5.5,六次甲基四胺,+,HCl,5.13,4.5,6.0,H,2,PO,4,-,+HPO,4,2-,7.21,6.5,8,三羟甲基甲胺,+,HCl,8.21,7.5,9,硼砂,(,H,3,BO,3,+H,2,BO,3,-,),9.24,8.5,10,NH,4,+,+NH,3,9.25,8.5,10,6,3.4.3,缓冲溶液的配制方法,1.,按比例加入,HA,和,A,(,NaAc,+,HAc,NH,4,Cl+NH,3,);,2.,溶液,中,H,+,大,加过量,A,-,溶液中,OH,-,大,加过量,HA;,3.,溶液中有,HA,可加,NaOH,中和一部分,溶液中有,A,可加,HCl,中和一部分,;,形成,HA-A,-,共轭体系,7,配制缓冲溶液的计量方法,方法,1,:(,确定引入酸,or,碱,),1.,按所需,pH,求,c,a,/,c,b,:pH,0,=,p,K,a,+,lg,(,c,b,/,c,a,);,2.,按引入的酸,(,碱,),量,c,a,及,pH,变化限度计算,c,a,和,c,b,:,3.,据,c,a,c,b,及所需溶液体积配制溶液,.,8,方法,2,:(,确定引入酸,or,碱,),1.,分别计算,pH,0,和,pH,1,时的,x,(HA),、,x,(A),2.,引入酸的量,c,(,HCl,)=,x,(HA),c,总,(,引入碱的量,c,(,NaOH,)=,x,(A),c,总,),求出,c,总,3.,pH,0,时,c,a,=,c,总,x,(HA),c,b,=,c,总,x,(A),9,方法,3,:(,引入酸碱均适用,),1.,根据引入的酸,(,碱,),量求,2.,根据所需,pH,求总浓度,c,:=2.3,c,x,0,x,1,3.,按,x,0,与,x,1,的比值配成总浓度为,c,的缓冲溶液,.,10,例,3.17,(,p88),欲制备,200,mL,pH=9.35,的,NH,3,-NH,4,Cl,缓冲溶液，且使该溶液在加入,1.0,mmol,的,HCl,或,NaOH,时，,pH,的改变不大于,0.12,单位，需用多少克,NH,4,Cl,和多少毫升,1.0,mol/L,氨水？,p,K,b,(NH,3,)=4.75,11,解,又,m,(NH,4,Cl)=,c,x,(NH,4,+,),V,M,(NH,4,Cl),V,(NH,3,)=,c,x,(NH,3,),V,/,c,(NH,3,),12,全域缓冲溶液,-,pH,图,0 2 4 6 8 10 12 14,pH,0.100,0.075,0.050,0.025,0.000,p,K,a,:3,5,7,9,11,五种弱酸,c,0.1mol/L,max,=,0.058,Britton-Robinson,缓冲溶液,(,H,3,PO,4,-,HAc,-H,3,BO,3,),13,3.4.4,常用标准缓冲溶液,(,p91),标准缓冲溶液的,pH,是,实验测定的,用于校准酸度计。,缓 冲 溶 液,pH,(25,o,C),饱和酒石酸氢钾,(0.034,molkg,-1,),3.557,邻苯二甲酸氢钾,(0.050,molkg,-1,),4.008,0.025,molkg,-1,KH,2,PO,4,+,0.025molkg,-1,Na,2,HPO,4,6.865,硼砂,(0.010,molkg,-1,),9.180,饱和氢氧化钙,12.454,14,3.5,酸碱指示剂,(p93),甲基橙,Methyl Orange(,MO,),(CH,3,),2,N,(CH,3,),2,N=,N=N,H,=N,N,SO,3,-,SO,3,-,OH,-,H,+,+,红,3.1,-,4.0(,橙,),-,4.4,黄,p,K,a,=3.4,3.5.1,作用原理,:,酸形和碱形具有不同的颜色,.,15,甲基橙,的,x,-pH,图,(,p95),0 2 4 6 8,pH,p,K,a,=3.4,pT,=4.0,(,滴定指数,),红,橙,黄,3.1 4.4,0.66,0.34,0.91,0.09,0.8,0.2,1.0,0.5,0.0,x,16,MO,MR,PP,3.1,4.4,4.4,6.2,8.0,9.6,4.0,pT,5.0,pT,=,p,K,a,9.0,常用单一酸碱指示剂,(,要记住,),百里酚酞,:,无色,9.4-,10.0(,浅蓝,),-,10.6,蓝,17,混合指示剂：,甲基红,+,溴甲酚绿,5.0,-,-,-5.1,-,5.2,暗红,灰,绿,用于,Na,2,CO,3,标定,HCl,时,指示终点,由于颜色互补使变色间隔变窄,变色敏锐,.,18,3.5.2,影响指示剂变色间隔的因素,1.,指示剂用量,:,宜少不宜多,看清颜色即可,2.,温度,:,温度影响,p,K,a,影响变色间隔,一般应室温滴定,3.,盐类,:,离子强度影响,p,K,a,19,3.6,酸碱滴定曲线和指示剂的选择,选择指示剂的原则,:,指示剂的变色点尽可能与化学计量点接近，以减小滴定误差。在滴定,突跃,范围变色的指示剂可使滴定,(,终点,),误差,小于,0.1%,。,直接滴定,：指示剂在化学计量点,前,变色，误差为,；,指示剂在化学计量点,后,变色，误差为,。,返滴定,：,滴定曲线：,溶液,pH,随中和百分数（,T,%,）,变化的曲线。,误差符号相反。,20,3.6.1,强酸碱滴定,0.10,molL,-1,NaOH,滴定,20.00,mL,0.10molL,-1,HCl,H,+,+OH,-,=H,2,O,K,t,=1/,K,w,=10,14.00,-,0.1%,时,:,pH=4.30,2.,滴定开始到,sp,前,:,H,+,=,c,(,HCl,)(,未中和,),1.,滴定前,:,H,+,=,c,(,HCl,)=,0.1000molL,-1,pH=1.00,21,3.sp,时,:,H,+,=OH,-,pH=7.00,4.,sp,后,:,OH,-,=,c,(,NaOH,)(,过量,),+,0.1%,时,:,H,+,=2.010,-10,molL,-1,pH=9.70,22,0.1000molL,-1,NaOH,滴定,20.00,mL,0.1000molL,-1,HCl,(p99),NaOH,mL,T%,剩余,HCl,mL,过量,NaOH,pH,H,+,计算,0.00,0,20.0,1.00,滴定前,:,H,+,=,c,(,HCl,),18.00,90.0,2.00,2.28,sp,前,:,H,+,=,19.80,99.0,0.20,3.00,19.98,99.9,0.02,4.30,sp:H,+,=OH,-,=10,-7.00,20.00,100.0,0.00,0.00,7.00,20.02,100.1,0.02,9.70,20.20,101.0,0.20,10.70,sp,后,:,OH,-,=,22.00,110.0,2.00,11.68,40.00,200.0,20.00,12.52,突跃,23,强酸碱滴定曲线,(,p99),0.10,molL,-1,NaOH,0.10molL,-1,HCl,0.10,molL,-1,HCl,0.10molL,-1,NaOH,pH,12,10,8,6,4,2,0,0 100 200%,滴定百分数,T%,9.7,sp+0.1%,4.3 sp-0.1%,sp,7.0,突跃,9.0,5.04,.,0,9.8,8.0,3.1,*,6.2,*4.4,PP,MR,MO,PP 9.0,MR 6.2,MO 4.4,PP 8.0,MR 5.0,24,不同浓度,的强碱滴定强酸的滴定曲线,(,p101),NaOH,HCl,0 100 200%,pH,12,10,8,6,4,2,10.7,9.7,8.7,7.0,5.3,4.3,3.3,PP,MR,MO,5.0,4.4,9.0,6.2,4.4,3.1,.01,molL,-1,0.1molL,-1,1molL,-1,浓度增大,10,倍，突跃增加,2,个,pH,单位。,25,3.6.2,一元弱酸碱的滴定,(,K,a,(,HAc,)=10,-4.76,K,a,(HA)=10,-7.00,),NaOH,mL,T%,组成,pH,HAc,pH,HA,H,+,计算式,0,0,HA,2.88,4.00,与滴定强酸的,pH,相同,10.00,50.0,HA+A,-,4.76,7.00,18.00,90.0,HA+A,-,5.71,7.95,19.80,99.0,HA+A,-,6.67,9.00,19.96,99.8,HA+A,-,7.46,9.56,19.98,99.9,HA+A,-,7.76,9.70,20.00,100.0,A,-,8.73,9.85,20.02,100.1,A,-,+OH,-,9.70,10.00,20.04,100.2,A,-,+OH,-,10.00,10.13,20.20,101.0,A,-,+OH,-,10.70,10.70,22.00,110.0,A,-,+OH,-,11.68,11.68,-,0.1%:pH=,p,K,a,+3,26,强碱,滴定,弱酸,滴定曲线,(,p103),0.10,molL,-1,NaOH,HAc,0.10molL,-1,0 100 200,T%,pH,12,10,8,6,4,2,0,HAc,Ac,-,
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