THI KIM TRA GIA K MN HA PHN TCH LP HA 2010 THI GIAN 60 PHT KHNG K 5 PHT C 1.Cn bng ion: 7.0 im a.Hy vit cc phng trnh biu din phn ng trao i proton trong dung dch nc ca cc cht sau (1.0 im) i.Potassium hydroxide: KOH K++OH- ii.Acid formic: HCOOHH++HCOO- iii.Potassium hydrogen phthalate:KOOC-C6H4-COOH K++-OOC-C6H4-COOH -OOC-C6H4-COOHH+ +-OOC-C6H4-COO- Ka2 -OOC-C6H4-COOH+ H2O OH- +HOOC-C6H4-COOH Kb2 iv.Potassium dihydrogen phosphate: KH2PO4 K++H2PO4- H2PO4- H+ +HPO42- Ka2 HPO42- H+ +PO43- Ka3 H2PO4-+ H2O OH- +H3PO4 Kb3 b.Gi s phc gia ion Cu2+ v NH3 c s phi tr cc i l 4. Hng s phn ly tng nc ca phc ln lt l K1 = 10-2.11; K2 = 10-2.87; K3 = 10-3.48 v K4 = 10-4.11. (1 im) i.Hy vit cc cn bng phn ly ca cc phc Cu(NH3)i.Cu(NH3)42+Cu(NH3)32++ NH3

( ) | || |( ) | |424 3323 311|= =++NH CuNH NH CuKCu(NH3)32+Cu(NH3)22++ NH3

( ) | || |( ) | |323 3322 321|= =++NH CuNH NH CuKCu(NH3)22+Cu(NH3)2++ NH3

( ) | || |( ) | |222 332331|= =++NH CuNH NH CuKCu(NH3)2+Cu2++ NH3

| || |( ) | |1233241|= =++NH CuNH CuK ii.Hy tnh hng s bn 1-i ca cc phc Cu(NH3)i.- Phc Cu(NH3)2+c 11 . 441101= =K|- Phc Cu(NH3)22+c 59 . 73 42 1 2 1101* = = =K K| | |- Phc Cu(NH3)32+c 46 . 102 3 43 2 1 3 1101* * = = =K K K| | | |- Phc Cu(NH3)32+c 57 . 121 2 3 44 3 2 1 4 1101* * * = = =K K K K| | | | | c.Hy tnh pH trong cc trng hp sau (2.0 im) i.HCl 0.001 M: HCl H++Cl-. Ca >> 10-6M [H+] = Ca pH =-lg[H+] = 3 ii.KCN 0.01 M, cho 4 . 9 =HCNapK : KCN K++CN- CN-+H2OHCN +OH-pKb = 14 pKa = 4.6 H2OH+ +OH-pKw = 14 Xem CN- nh n baz | || | | || | | |+ + + =H OHH OH CK OHbb

-| | | |7 . 10 3 . 3 2 6 . 410 10 10 * 10 + = >> = = =g b b gH C K OH b qua phn ly ca nc. [OH-]g > Cb/100 = 10-4 phn CN- phn ng vi nc l ng k so vi Cb. | || || |=OHOH CK OHbb ; gii phng trnh bc 2 pH = 10.53 iii.NaHCO3 0.1 M, cho bit H2CO3 c pK1 = 6.35, pK2=10.33 NaHCO3 Na++HCO3-. HCO3-H+ +CO32-. pKb2 = 14 - pKa1 = 7.65 HCO3-+H2OH2CO3 +OH-pKa2 H2OH+ +OH-pKw = 14 y l mui c anion lng tnh, pH = 0.5(pKa1+pKa2) = 8.35 iv.H2SO4 0.05 M bit K2 = 10-1.99. H2SO4 H++HSO4- HSO4-H+ +SO42-

| || || | +=4242HSOSO HKH2OH+ +OH-pKw = 14 y c th uc xem nh hn hp acid mnh v acid yu, nuc phn ly khng ng k Phng trnh bo ton proton: [H+]= [H+]nc 1 + [H+]nc 2=Ca + [SO42-] = | |22K HC KCaa+++ Gii phng trnh bc 2: [H+] = 0.0574 M pH = 1.24 d.Ha tan 15.6 g NaH2PO4.2H2O v 17.8 g Na2HPO4.2H2O vo nc v pha long thnh 1L (dung dch A). Cho bit H3PO4 c pK1 = 2.12, pK2=7.21 v pK3=12.36 (1.5 im) i.Hy tnh pH ca dung dch A. 1L dung dch A cha 0.1 mol acid yu H2PO4- v 0.1 mol baz lin hp HPO42- tc l A l dung dch m. | || |21 . 7 lg4 2242= + =PO HHPOpK pHa ii.Nu thm 15 mL NaOH 10 M vo 1 L dung dch A (gi s h s pha long khng ng k), hy tnhpH ca dung dch. S mol NaOH thm vo:mol nOH15 . 0100010 * 15= = Phng trnh phn ng: H2PO4-+OH- HPO42-+ H2O do >4 2PO HNaOHn n nn H2PO4- phn ng ht; HPO42-+OH- PO43-+ H2O. mol n ndu NaOHPO05 . 0 1 . 0 15 . 0,34= = =. Lc ny dung dch c:mol n mol nHPO PO15 . 0 05 . 0 1 . 0 ; 05 . 02434= + = = y l dung dch m. | || |88 . 1115 . 005 . 0lg 36 . 12 lg24343= + = + =HPOPOpK pHa e.Cho dung dch EDTA Na2H2Y 0.01 M. (1.5 im) i.Hy tnh nng ca cc cu t H+, HiY (i=04) trong dung dch. Cho bit H4Y c pK1 = 2.0, pK2=2.7, pK3=6.7 v pK4=10.3 Cc cn bng phn ly: Na2H2Y 2Na++H2Y2-. H2Y2-H+ +HY3- pKa3 HY3-H+ +Y4- pKa4 H2Y2- + H2OH3Y- +OH-pKb3 H3Y- + H2OH4Y +OH-pKb4 H2OH+ +OH-pKw = 14 y l mt mui cha anion lng tnh, pH = 0.5(pKa2 + pKa3) = 4.7 | || || | | | | | | |7 . 64 3 2 1 3 2 1 2 1213 44410+ + + ++=+ + + += CK K K K K K K H K K H K H HHY H| || || | | | | | | |44 3 2 1 3 2 1 2 1213 413310+ + + ++=+ + + += CK K K K K K K H K K H K H HK HY H| || || | | | | | | |01 . 24 3 2 1 3 2 1 2 1213 42 12210+ + + ++=+ + + += CK K K K K K K H K K H K H HK K HY H| || || | | | | | | |44 3 2 1 3 2 1 2 1213 43 2 110+ + + ++=+ + + += CK K K K K K K H K K H K H HK K K HHY| || | | | | | | |6 . 94 3 2 1 3 2 1 2 1213 44 3 2 110+ + + +=+ + + += CK K K K K K K H K K H K H HK K K KYii.Nu trn ln 50 mL dung dch Ni2+ 0.01 M vi 50 mL dung dch Na2H2Y 0.02 M ti pH = 4.7; hy tnh tt c cc dng HiY (i=04) v NiY. Cho bit6 . 18 =NiYpK . Phn ng: Ni2++ H2Y2- NiY2- + 2H+ hay Ni+Y NiY Ti pH 4.7 c 61 . 77 . 218 . 187 . 191 . 14174 . 93 . 107 . 4) (10101010101010101011= + + + + =H Yo Hng s cn bng iu kin: | || |||| || || |7 9 . 10) ( ) ( ) (10 101' '' > = = = = =H YNiYH Y cb H YKKY NiNiYY NiNiYK o o o , nh vy phn ng gia Ni v EDTA l hon ton. [NiY] = CNi = 0.5*0.01 = 0.005 M [H2Y]d = 0.5*(CH2Y [NiY]) = 0.005 M. Nh vy nng cc cu t [HiY] ging nh cu a vi C = 0.005 M [H4Y]=10-7M; [H3Y]=10-4.3M; [H2Y]=10-2.31M; [HY]=104.3M; [Y]=10-9.9M. 2.nh phn acid: 3 im a.Chun dung dch HCl 0.1 N bng NaOH (0.1032 0.0019) N. Hy xc nh iu kin chun vi chnh xc >99.9%? Xc nh khong bc nhy ca php chun qua cc F = 0.999; F = 1.000 v F = 1.001? Tnh sai s im cui nu dng cc ch th methyl cam (pT = 4) v phenolphthalein (pT=8.3)? (1.0 im) Phng trnh chun : H++ OH- H2O iu kin chun NQ 99.9%. ng cong chun :- F = 0.999 dung dch c 99.9%CoD NaCl v 0.1% CoD HCl: dung dch n acid mnh + mui trung tnh pH = -lg 0.1%CoD = 4.3 - F = 1.000 dung dch c 100%CoD NaCl: mui trung tnh pH = 7. - F = 1.001 dung dch c 100%CoD NaCl v 0.1% CoD NaOH: dung dch n baz mnh + mui trung tnh pH = 14-lg 0.1%CoD = 9.7 khong bc nhy: 4.3 9.7. Sai s ch th:- Nu dng methyl cam (pT=4): ch th i mu trc im tng ng, sai s thiu, % 2 . 02 * 1 . 0100 * 105 . 0 * 1 . 0100 * 10 100 * 1014 4%, = = = ~ A < +D CFopTH Indcui

Nu dng phenolphthlein (pT=8.3): ch th i mu sau im tng ng, sai s tha, % 004 . 05 . 0 * 1 . 0100 * 10 100 * 1017 . 5 14%,= + = + ~ A > D CFopTOH Indcui b.Thc hin php chun lp 4 ln, mi ln vi 10.00 mL dung dch mu HCl. Th tch NaOH tiu tn ln lt l 10.25; 10.30; 10.20 v 10.30 mL. Hy tnh nng HCl c km theo khong bt n. Bit rng pipet 10 mL c = 0.02 mL, t0.95;3=3.18; u0.95 = 1.96(1.0 im). mL V NaOH 2625 . 10 = ; S4 = 0.04787 076 . 0404787 . 018 . 343 ; 95 . 0 = = =nStNaOH VcVHCl = 10 mL,0266 . 0302 . 096 . 195 . 0 = = =nuHClVoc) ( 105909 . 0102625 . 10 * 1032 . 0NVV CCHClNaOHNaOHHCl= = =02 . 01002266 . 02625 . 10076 . 01032 . 00019 . 02 2 22 2 2=|.|

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\|=HClVNaOHVNaOHCHClCV V C CHCl NaOH NaOH HClc c c c 0021 . 0 105909 . 0 * 02 . 0 02 . 0 = = =HClHClCHClCCcc CHCl = 0.1059 0.0021 (N) c.Trong php chun trn ngi ta c th dng cht gc Na2CO3 thay cho NaOH. Hy xc nh iu kin chun , khong bc nhy pH trong tnh hung ny chng minh rng Na2CO3 ph hp cho php chun ny vi ch th methyl cam (pT 4.0) hoc ch th Tashiro pT 5.4. Bit rng H2CO3 c pK1 = 6.35, pK2=10.33, tan ca CO2 nhit phng l 0.001 M? (1.0 im). Phn ng: CO32-+ H+ HCO3-. HCO3+ H+ H2CO3 CO2+H2O. Do acid carbonic c 2 nc c pK < 4 nn ch c th chun tng hai nc t chnh xc cao. Gi s nng Na2CO3 l 0.05M, iu kin chun : pKb + pCo + pDF=2 = 7.65 + 1.3 + 0.3 = 9.25 < 10. khng th chun vi chnh xc >99.9% m ch min cng vi chnh xc 99% m thi, nh vy sodium carbonate cha phi l cht gc tt??? Thc t do tnh cht c bit ca acid carbonic: phn hy thnh kh carbonic v thot ra khi h phn ng. F = 1.99: dung dch c 1% CoD NaHCO3 = 0.0005 M v 99% CoD H2CO3 = 0.0495 M > 0.001 M mt phn ln H2CO3 thot ra khi h dng CO2. Dung dch phn ng c tnh m. | || |05 . 6001 . 00005 . 0lg 35 . 6 lg3 231= + = + =CO HHCOpK pHa F = 2.00: dung dch c 100% CoD H2CO3 = 0.05 M > 0.001 M, ly| | M CO H 001 . 03 2=pH = 4.675 (xem nh n acid yu). F = 2.01: dung dch cha 100% CoD H2CO3 v 1% CoD HCl = 0.01*0.05*0.5 = 0.00025 M: xem nh ch c HCl pH = -lg 0.00025 = 3.60. Khong bc nhy l 3.6 6.05 vi chnh xc 99%. Trong thc t khi thc hin chun ny ngi ta thng un nng dung dch ui ht H2CO3, gi s nng H2CO3 trong dung dch lc ny cn 10-5M, lc ny tiF = 1.99: dung dch c 1% CoD NaHCO3 = 0.0005 M v 99% CoD H2CO3 = 0.0495 M > 0.00001 M mt phn ln H2CO3 thot ra khi h dng CO2. Dung dch phn ng c tnh m. | || |05 . 800001 . 00005 . 0lg 35 . 6 lg3 231= + = + =CO HHCOpK pHa F = 2.00: dung dch c 100% CoD H2CO3 = 0.05 M > 0.00001 M, ly| | M CO H 00001 . 03 2=pH = 5.675 (xem nh n acid yu). Khong bc nhy trong trng hp ny l 3.6 8.05 (99%) hay 4.6 7.05 (99.9%), chnh xc ca php chun tng ln v c th dng ch th hn hp Tashiro pT 5.4 c chnh xc tt nht. HT