地化環(huán)科分析化學(xué)

1、甲基紅Methyl Red (MR)CH3 CH3CH3CH3COO-N=NNNN=N COOHH+OH-H+pH6.2pKa=5.2pH4.4酚酞 Phenolphthalein (PP)OH- OCCO- COO-HOOH COOOH-H+(pH10)混合指示劑Mixed indicators：甲基紅+溴甲酚綠5.0-5.1-5.2暗紅灰綠用于Na2CO3標(biāo)定HCl時指示終點由于顏色互補使變間變窄, 變色敏銳.MOMRPP4.0pT4.46.25.0pT=pKa8.09.69.0常用單一酸堿指示劑3.14.4百里酚酞: 無色 9.410.0(淺藍)10.6藍例：強堿滴定強酸 0.1000m

2、olL-1 NaOH滴定 20.00mL 0.1000molL-1 HCl0.1000molL-1 NaOH滴定20.00mL 0.1000molL-1 HClNaOHmLT%剩余HCl mL過量NaOHpHH+計算0.00020.01.00滴定前:H+=c(HCl)18.0090.02.002.28sp前:H+= caVa - cbVbVa +Vb19.8099.00.203.3019.9899.90.024.30突sp:H+=OH-躍=10-7.0020.00100.00.000.007.0020.02100.10.029.7020.20101.00.2010.70cbVb -caVasp

3、后:OH-=Va +Vb22.00110.02.0011.6840.00200.020.0012.52強堿滴定強酸0.10molL-1NaOH0.10molL-1HCl0.10molL-1 HCl0.10molL-1NaOHpH1210864200200%100滴定百分?jǐn)?shù),T% 9.7sp+0.1%4.3sp-0.1%躍9.9.68.00sp7.0 突PPMR*6.2*4.4 5.MO 3.1 04.0PP 9.0MR 6.2MO 4.4PP 8.0MR 5.0強酸滴定強堿NaOHHCl0200%100滴定百分?jǐn)?shù)不同濃度的強堿滴定強酸的滴定曲線pH1210864210.79.78.77.04.

4、33.3PPMRMO4.49.06.25.34.4 5.03.1.01molL-1 0.1molL-1 1molL-1濃度增大10倍，突躍增加 2個pH單位。Comparison of two weak acids(Ka,HAc=10-4.76,Ka,HA=10-7.00)NaOHmLT%組成pHHAcpHHAH+計算式00HA2.884.00H+ =K caaH+ = HA KA- a-0.1%:pH=pKa+3OH- =Kc(A- )b以過量NaOH計算10.0050.0HA+A-4.767.0018.0090.0HA+A-5.717.9519.8099.0HA+A-6.739.0019.

5、9699.8HA+A-7.469.5619.9899.9HA+A-7.749.7020.00100.0A-8.729.8520.02100.1A-+OH-9.7010.0020.04100.2A-+OH-10.0010.1320.20101.0A-+OH-10.7010.7022.00110.0A-+OH-11.6811.68滴定曲線 Titration curves0.10molL-1 NaOHHAc0.10molL-1200 T%100滴定百分?jǐn)?shù)pH121086420 0HAcAc-Ac-+OH-突躍6.29.78.77.74.34.45.0PP3.14.0MR MOHAcHCl突躍處于弱

6、堿性,只能選酚酞作指示劑.NaOH滴定HAcpH(Different concentrations)1molL-10.1molL-10.01molL-162810129.238.738.23HA4cHCl10.709 708.707.76突躍范圍緩沖容量050150T%100滴定百分?jǐn)?shù)4.76濃度增大 10倍，突躍增加1個 pH單位HA:9.7-10.0HAAA+OH-滴定突躍HCl:4.3-9.7HAc:7.7-9.7pH12108642HClHApKa=7HAc pKa=4.76OOOO10.09.77.76甲基紅O4.3 甲基橙050100滴定百分?jǐn)?shù)150200百里酚酞酚酞0.1molL

7、-1NaOH滴定0.1molL-1 HA(Ka不同)Ka增大10倍，突躍增加一個 pH單位對于0.1molL-1 的HA,Ka10-7才能準(zhǔn)確滴定.即cKa10-80.1molL-1HClNH30.1molL-1pKb=4.75050100150200%6.255.284.306.24.43.1pHNaOHNH3突躍處于弱酸性,選甲基紅或甲基橙作指示劑.強酸滴定弱堿8.00.100molL-1NaOH滴定多元酸的滴定曲線AH3PO442061081214102030B. H2C2O440AB C5060NaOH加入量C. H2SO4B和CApH200300400(T%)0.5%有時可更大些0.

8、5%有時可更大些lgKapKa2.167.2112.325.055.11pHsp1= 4.7pHsp2= 9.70100H3PO4H2PO4 -HPO42-PO43-5.04.4H3A+H2A-H2A-+HA2-HA2-+A3-10.09.4A3-+NaOHpHsp3sp2sp1NaOH滴定0.1molL-1H3PO4NaOH滴定H3PO4 時指示劑的選擇H3PO44HPO 2-PO 3-4pHsp2= 9.7百里酚酞至淺藍(pH=10.0)H2PO4-pHsp1= 4.7MO至黃 (4.4)(同濃度NaH2PO4參比)pKa1(2.16)pKa2(7.21)pKa3(12.32)酸堿滴定法結(jié)

9、果計算示例例1：分析某混合堿,稱取0.3419g試樣,溶于水后,以酚酞為指示劑時,用0.1000mol/LHCl標(biāo)準(zhǔn)溶液滴定至終點,用去酸標(biāo)準(zhǔn)溶液23.10mL,再加甲基橙指示劑,繼續(xù)滴定至終點,又消耗酸溶液 26.81mL.試計算試樣由何組份組成?各組份的百分含量為多少?(NaOH 40.01,Na2CO3 105.99,NaHCO3 84.01)例2：稱取Na2CO3和K2CO3的混合物0.1801g,溶解后以甲基橙為指示劑,用0.1000mol/LHCl標(biāo)準(zhǔn)溶液滴定,用去31.55mL.求樣品中Na2CO3和K2CO3的含量。 (Na2CO3 105.99,K2CO3138.21)解:設(shè)

10、樣品中含Na2CO3為xg,含K2CO3為yg.根據(jù):Na2CO3+2HCl =2NaCl+H2O+CO2K2CO3+2HCl = 2KCl +2H2O+CO2有:x+y =0.1801 2(x/105.99 + y/138.21) = 0.100031.5510-3 聯(lián)立解得x = 0.1248(g)y =0.0553(g)即:Na2CO3% = (0.1248/0.1801)100% = 69.29%K2CO3%= (0.0553/0.1801)100% = 30.70%例3：有一試樣重3.00g,可能含有Na3PO412H2O,Na2HPO412H2O,NaH2PO4H2O中一種或這些化合物可能的混合物。用甲基橙為指示劑,以0.5000mol/LHCl溶液滴定時需14.00mL.同樣重量以酚