第六讲 H离子浓度的计算3.ppt

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,*,*,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,*,3.3,酸碱溶液,H,+,的计算,酸碱溶液的几种类型,一,.,强酸碱,二,.,一元弱酸碱,HA,多元弱酸碱,H,2,A,H,3,A,三,.,两性物质,HA,-,四,.,共轭酸碱,HA+A,-,五,.,混合酸碱,强,+,弱,.,弱,+,弱,4,一、强酸、碱溶液,强酸,(,HCl,):,强碱,(,NaOH,):,c,HCl,=10,-5.0,或,10,-8.0,molL,-1,pH=?,质子条件,:H,+,+,c,NaOH,=OH,-,最简式,:OH,-,=,c,NaOH,质子条件,:H,+,=,c,HCl,+OH,-,最简式,:H,+,=,c,HCl,展开则得,H,+,浓度的,精确公式,数学处理麻烦,!,质子条件式,:,H,+,=A,-,+OH,-,平衡关系式,精确表达式,:,H,+,K,a,HA,+,K,w,H,+,=+,H,+,K,a,HA,H,+,K,w,H,+,+,K,a,c,a,H,+,HA=,H,+,3,+,K,a,H,+,2,-(,K,a,c,a,+,K,w,)H,+,-,K,a,K,w,=0,若,:,K,a,c,a,10,K,w,忽略,K,w,(,即忽略水的酸性,),HA=,c,a,-A,-,=,c,a,-(H,+,-OH,-,),c,a,-H,+,近似计算式,:,展开得一元二次方程,H,+,2,+,K,a,H,+,-,c,a,K,a,=0,，求解即可,最简式,:,若,:,c,a,/,K,a,100,则,c,a,-,H,+,c,a,H,+,K,a,HA,+,K,w,精确表达式：,H,+,K,a,(c,a,-H,+,),H,+,K,a,c,a,若,:,K,a,c,a,10,K,w,但,c,a,/,K,a,100,酸的解离可以忽略,HA,c,a,得近似式,:,H,+,K,a,HA,+,K,w,精确式：,H,+,K,a,c,a,+,K,w,(1),K,a,c,a,10,K,w:,(2),c,a,/,K,a,100,:,(3),K,a,c,a,10,K,w,c,a,/K,a,100,:,H,+,K,a,HA,+,K,w,精确表达式：,H,+,K,a,(c,a,-H,+,),H,+,K,a,c,a,+,K,w,(,最简式,),H,+,K,a,c,a,例,计算,0.20molL,-1,Cl,2,CHCOOH,的,pH.(p,K,a,=1.26),如不考虑酸的离解,(,用最简式,:pH=0.98),解,:,K,a,c,=10,-1.26,0.20=10,-1.96,10,K,w,c,/,K,a,=0.20/10,-1.26,=10,0.56,100,故近似式,:,解一元二次方程,:H,+,=10,-1.09,则,pH=1.09,H,+,K,a,(c,a,-H,+,),2.,一元弱碱,(B,-,),质子条件,:,得精确表达式,:,H,+,+HB=OH,-,H,+,+=,K,a,H,+,B,-,H,+,K,w,H,+,K,w,1+B,-,/,K,a,酸碱平衡关系,若,:,c,/,K,a,20,“1”,可以忽略,(,水的碱性,),并且,:B,-,=,c,b,-HB=,c,b,(OH,-,-H,+,),c,b,OH,-,近似计算式,:,最简式,:,若,K,b,/,c,b,10,K,w:,(2),c,/,K,b,100,:,(3),K,b,c,10,K,w,c,/,K,b,100,:,OH,-,=,K,b,(,c,b,-OH,-,),OH,-,=,K,b,c,b,+,K,w,H,+,=,K,a,K,w,c,b,OH,-,=,K,b,c,b,最简式,:,二元弱酸,(H,2,A),质子条件,:,H,+,=HA,-,+2A,2-,+OH,-,2,K,a2,H,+,=,K,a1,H,2,A (1+)+,K,w,H,+,酸碱平衡关系,K,w,K,a1,H,2,A,H,+,=+,2,K,a1,K,a2,H,2,A,H,+,H,+,2,H,+,0.05,可略,近似式,:,以下与一元酸的计算方法相同,K,a1,c,a,10,K,w,2,K,a2,H,+,=,K,a1,H,2,A (1+)+,K,w,H,+,2,K,a2,H,+,=,K,a1,H,2,A (1+)+,K,w,H,+,2K,a2,H,+,2K,a2,H,+,H,+,=,K,a1,H,2,A,(,忽略二级及以后各步离解,),K,a1,c,a,10,K,w,，,则：,0.05,则：,c,a,/,K,a1,100,计算饱和,H,2,CO,3,溶液的,pH,值,(0.040 mol/L),H,+,K,a1,c,a,2,K,a2,H,+,=,K,a1,H,2,A (1+),H,+,H,+,=,K,a1,H,2,A,2K,a2,H,+,2K,a2,K,a1,c,a,18,三、两性物质溶液,两性物质：,在溶液中既起酸,(,给质子,),、又起碱（得质子）的作用,多元酸的酸式盐,Na,2,HPO,4,NaH,2,PO,4,弱酸弱碱盐,NH,4,Ac,氨基酸,质子条件,:H,+,+H,2,A=A,2,-,+OH,-,精确表达式,:,酸碱平衡关系式,1.,酸式盐,NaHA,K,w,H,+,HA,-,H,+,+=+,K,a2,HA,-,K,a1,H,+,H,+,H,+,K,a1,(,K,a2,HA,-,+,K,w,),K,a1,+HA,-,若,:,K,a1,K,a2,HA,-,c,(,p,K,a,3.2),近似计算式,:,如果,c,10,K,a1,则“,K,a1,”,可略,得,最简式,:,H,+,=,K,a1,K,a2,c,K,a1,+c,H,+,=,K,a1,(,K,a2,c,K,w,),K,a1,+,c,若,K,a2,c,10,K,w,则,K,w,可忽略,H,+,K,a1,K,a2,精确式：,K,a1,K,a2,HA,-,c,K,a2,c,1,0,K,w,c,10,K,a1,pH=1/2(p,K,a1,+p,K,a2,),H,+,K,a1,(,K,a2,c+,K,w,),K,a1,+c,H,+,K,a1,K,a2,c,K,a1,+c,H,+,K,a1,K,a2,H,+,K,a1,(,K,a2,HA,-,+,K,w,),K,a1,+HA,-,2.,弱酸弱碱盐,NH,4,Ac,质子条件式,:,H,+,+,HAc,=NH,3,+OH,-,K,a,c,10,K,w,c,10,K,a,H,+,K,a,(,K,a,c+,K,w,),K,a1,+c,酸碱平衡关系,NH,4,+,Ac,-,c,H,+,=,K,a,K,a,c,K,a,+c,H,+,K,a,K,a,K,a,NH,4,+,K,a,HAc,例,计算,0.0010 mol/L CH,2,ClCOONH,4,溶液的,pH,CH,2,ClCOOH:,K,a,=1.410,-3,NH,3,:,K,b,=1.810,-4,K,a,=5.610,-10,K,a,c,10,K,w,c,10,K,w,c,/,K,a1,10,H,+,K,a1,K,a2,c,K,a1,+c,H,+,K,a1,(,K,a2,c+,K,w,),K,a1,+c,酸碱平衡关系,H,+,K,a1,K,a2,H,+,=,K,a,=,K,a,HA,A,-,c,a,-H,+,+OH,-,c,b,+H,+,-OH,-,H,+,=,K,a,HA,A,-,c,a,mol,/L HA+,c,b,mol,/L,NaA,PBE,：,HA=,c,a,+OH,-,-H,+,A,-,=,c,b,+H,+,-OH,-,物料平衡,:HA+A,-,=,c,a,+,c,b,电荷平衡,:H,+,+Na,+,=OH,-,+A,-,HA=,c,a,-H,+,+OH,-,A,-,=,c,a,+,c,b,-HA,=,c,b,+H,+,-OH,-,+),pH 8(,碱性,),略去,H,+,若,c,a,20H,+,;,c,b,20H,+,或,c,a,20OH,-,;,c,b,20OH,-,最简式,H,+,=,K,a,c,a,c,b,计算方法：,(1),先按最简式计算,OH,-,或,H,+,。,(2),再计算,HA,或,A,-,看其是否可以忽略,.,如果不能忽略,再按近似式计算。,通常情况下，由共轭酸碱对组成的缓冲溶液可以用最简式直接计算,pH,例,(1)0.10 mol/L NH,4,Cl 0.20 mol/L NH,3,先按最简式,:,(2),0.080 mol/L,二氯乙酸,0.12mol/L,二氯乙酸钠,先用最简式求得,H,+,0.037 mol/L,c,a,OH,+,c,b,OH,-,结果合理,pH=9.56,应用近似式,:,解一元二次方程，,H,+,=10,-1.65,molL,-1,pH=1.65,pH=,p,K,a,+,lg,=9.56,c,a,c,b,H,+,=,K,a,c,a,-H,+,c,b,+H,+,强酸,(,HCl,)+,弱酸,(HA),质子条件,:H,+,=,c,HCl,+A,-,+OH,-,(,近似式,),忽略弱酸的离解,:H,+,c,HCl,(,最简式,),K,w,H,+,=,c,HCl,+,K,a,c,a,K,a,+H,+,H,+,酸碱平衡关系,强碱,(,NaOH,)+,弱碱,(B,-,),质子条件,:H,+,+HB+,c,NaOH,=OH,-,忽略弱碱的离解,:,OH,-,c,(NaOH,),(,最简式,),K,w,OH,-,=,c,HCl,+,K,b,c,b,K,b,+OH,-,OH,-,两弱酸,(HA+HB),溶液,质子条件,:,H,+,=A,-,+B,-,+OH,-,HA,c,HA,HBc,HB,酸碱平衡关系,K,w,K,HA,HA,H,+,=+,K,HB,HB,H,+,H,+,H,+,H,+,K,HA,c,HA,H,+,K,HA,c,HA,+,K,HB,c,HB,K,HA,c,HA,K,HB,c,HB,弱酸,+,弱碱,(HA+B,-,),溶液,质子条件,:,H,+,+HB=A,-,+OH,-,HA,c,HA,HBc,HB,酸碱平衡关系,K,w,H,+,HB,H,+,+=+,K,HA,HA,K,HB,H,+,H,+,H,+,K,HA,K,HB,c,HA,/c,B,综合考虑、分清主次、合理取舍、近似计算,酸碱溶液,H,+,的计算总结,质子条件,物料平衡,电荷平衡,酸碱平衡关系,H,+,的精确表达式,近似处理,H,+,的近似计算式和最简式,甲基橙,(,MO,),一、,作用原理,:,酸式和其共轭碱式具有明显不同的颜色,3.4,酸碱,指示剂,H,+,OH,-,红,3.1,橙,4.0,4.4,黄,p,K,a,=3.4,甲基橙的,-pH,图,0 2 4 6 8 pH,p,K,a,=3.4,红,橙,黄,3.1 4.4,0.66,0.34,0.91,0.09,0.8,0.2,1.0,0.5,0.0,二、,指示剂变色范围,HIn,H,+,+In,-,K,HIn,=,In,-,/,HIn,10,显示,In,-,色,In,-,/,HIn,0.1,显示,HIn,色,理论变色范围：,pH=,p,K,HIn,1,HIn,H,+,In,-,=,H,+,K,HIn,HIn,In,-,甲基橙,MO,甲基红,MR,酚酞,PP,3.1,4.4,4.4,6.2,8.0,9.6,4.0,5.0,9.0,常用单一酸碱指示剂,百里酚酞,:,无色,9.4-,10.0(,浅蓝,),-,10.6,蓝,三、,影响指示剂变色范围的因素,指示剂用量,:,宜少不宜多，,对单色指示剂影响较大,例：,50,100mL,溶液中,23,滴,PP,，,pH9,变色，,而,1015,滴,PP,，,pH8,变色,离子强度,：影响,p,K,HIn,温度,其他,四、混合指示剂,溴甲酚绿,甲基红,5.0,-,-5.1,-,5.2,橙红,灰,绿,（黄红）（绿,+,橙红）（蓝黄）,用于,Na,2,CO,3,标定,HCl,时指示终点,通过颜色互补，使变色范围变窄，变色更敏锐,40,注意问题：,1,、肉眼仅可在指示剂的理论变色范围内观察出指示剂颜色随,pH,的变化而变化。,例：甲基橙：,p,K,=3.4,实际变色范围,:,甲基橙,:3.14.4(,p,K,=3.4,）红,-,橙,-,黄,甲基红,:4.46.2(,p,K,=5.0,）红,-,橙,-,黄,酚酞：,8.210.0,（,p,K,=9.1,）无,-,粉,-,红,2,、在指示剂的变色范围内，,pH,起码改变,0.3,个,单位,时，肉眼才能观察出指示剂颜色的变化。,要记,住哦！,