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MT S BI TP TNG HP V TNH TON CN BNGGing vin hng dnPGS.TS: Nguyn nh LuynSinh vin thc hinL Th Ngc ThoHunh Th THong Th Tuyt GiangNin kho 2014 - 2016

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A. M U Ho hc phn tch l mt nghnh khoa hc v cc phng php xc nh thnh phn nh tnh, thnh phn nh lng, cu trc ca cc cht trong i tng nghin cu. Trong , phn tch nh tnh gip tnh ton nng cn bng cc cu t trong dung dch khi t trng thi cn bng nhm mc ch nh gi kh nng phn ng gia cc cht, cc yu t nh hng n phn ng . T , tm cch iu khin phn ng xy ra theo mun. tm hiu v phng php gii mt s bi tp tnh ton cn bng, chng ti tm hiu ti MT S BI TP TNG HP V TNH TON CN BNG

L THUYT LIN QUAN V TNH TON CN BNG

MT S BI TP TNG HP V TNH TON CN BNG www.PowerPointDep.netB. NI DUNG

CHNG 1: L THUYT LIN QUAN V TNH TON CN BNG

I. Cn bng trong dung dch axit-bazAxit mnh:Baz mnh:Axit yu, n chc:Baz yu, n chc:(1.1)(1.2)(1.3)(1.4)

Axit a chc:Baz a chc:

Gii PT bc cao (theo phng php tip tuyn Newton)Gii theo phng php gn ng lin tcVCch 1Cch 2Axit a chc:

Gii PT bc cao (theo phng php tip tuyn Newton)Gii theo phng php gn ng lin tcVCch 1Cch 2Baz a chc:

250C, ln = 2,303lg v p dng cho dung dch rt long:

II. Cn bng trong phn ng oxi ho-khXt bn phn ng:Phng trnh Nernst: - Cc yu t nh hng n cn bng oxi ho-kh: pH, cht to phc, cht t tan.(1.7)

Phng trnh tng qut:Ox1 + Kh2 Kh1 + Ox2- Khi(1.8) th phn ng oxi ha - kh xy ra.(1.9)- bit mc mnh-yu ca phn ng:

Xt cn bng:

Khi tch s tan KS - Tch s tan c vit di dng nng ,ta c:

Trong : fi l h s hot ca ion iIII. Cn bng trong phn ng to kt ta (1.10)(1.11)- Trong dung dch long, lc tng tc gia cc ion khng ng k fi 1, nn:

* Nu tan ln hn 10-4 th phi xt n nh hng ca lc ion hay phi tnh theo hot ).(1.12)

Khi c cc qu trnh ph Tch s tan iu kinVi(1.13)(1.14)(1.15)

Cn bng:KS S mS nSKhi :

Suy ra:

- Nu xt n cc qu trnh ph, th tan (S) ca AmBn c tnh theo tch s tan iu kin ( ):Mi quan h gia tan v tch s tan:(1.16)(1.17)

IV. Cn bng trong dung dch phc

LU * Cn bng:* Bi tp c nhiu cn bng :- Cn bng axit baz:

- Cn bng oxi ha kh:- Cn bng to kt ta:- Cn bng to phc:Cn bng chung: K = Ka.Kcb.KS.Kf

CHNG 2: MT S BI TP TNG HP V TNH TON CN BNG

I. Bi tp tng hp chng axit-baz v oxi ho-khCu 1: nh gi tnh oxi ha-kh ca cp trong mi trng natri hiro cacbonat - ngha l pH = 8; bit pH = 0 l +0,57 V.Vi h ny xy ra phn ng:Th oxi ho kh ca cp ny:Nh vy,

Cu 2: (trch [1]) Vit na phn ng ca hai cp NO3-/HNO2 v HNO2/NO trong mi trng axit. Chng minh rng HNO2 b phn hy trong mi trng pH = 0 n 6. Cho bit, 25oC:Cc na phn ng trong mi trng axit:

+ pH = 0 HNO2 b phn hy:+ pH = 6 HNO2 vn khng bn, b phn hy nh phng trnh (*).Vy: - pH c nh hng n th ca cp OXH-K. - t pH = 0 n pH = 6, HNO2 b phn hy theo phng trnh (*)

II. Bi tp tng hp chng axit baz v phc cht

III. Bi tp tng hp chng axit baz v kt taCu 1: Dung dch bo ho H2S c nng 0,1M. Hng s axit ca H2S: K1 = 1,0.10-7 v K2 = 1,3.10-13. Mt dung dch A cha cc cation Mn2+, Co2+ v Ag+ vi nng ban u ca mi ion u bng 0,01M. Ho tan H2S vo A n bo ho v iu chnh pH = 2 th ion no to kt ta?Cho: TMnS = 2,5.10-10, TCoS = 4,0.10-21, TAg2S = 6,3.10-50Ta c:Vi

Tch cc nng :Khng c kt ta MnSTo kt ta CoSTo kt ta Ag2SKhi pH = 2Kt lun: pH c nh hng n vic to kt ta ca cc cht

Cu 2: Bc oxalat c tch s tan trong nc l 10-10,46 ti pH = 7. Tnh tan ca bc oxalat trong dung dch axit c pH = 5. Hai hng s phn li ca axit oxalic ln lt l: Ka1 = 5,6.10-2 v Ka2 = 6,2.10-6

Ti pH = 7 th [H+] = 10-7

Ti pH = 5 th [H+] = 10-5

Kt lun: pH c nh hng n tan ca cc cht. pH cng gim th tan cng tng.

Cu 3: Hi phi thm bao nhiu ml dung dch H2SO4 1M vo 100ml dung dch BaCl2 0,1M bt u xut hin kt ta BaSO4? Tnh pH ti thi im ? Cho bit tch s tan ca BaSO4 l TBaSO4=1,26.10-10 v coi H2SO4 phn li hon ton.Nng ion SO42- khi bt u xut hin kt ta BaSO4

Nng do H2SO4 cung cp:

Cu 4: (trch) tan ca AgCl trong nc ct mt nhit nht nh l 1,81 mg/dm3 (dung dch). Thm HCl chuyn pH v 2,35, gi thuyt th tch dung dch sau khi axit ha vn gi nguyn v bng 1,00 dm3. Hy tnh xem tan ca AgCl gim i my ln sau khi axit ha dung dch ban u n khi c pH = 2,35.37BD+ Trong nc ct: S = 1,81 mg/dm3 = 1,26.10-5 mol/l KS(AgCl) = S2 = (1,26.10-5)2 = 1,59.10-10 (mol/l)2+ Trong dung dch c pH = 2,35: Ta c cn bng:

Thay cc gi tr KS v pH ta thu c S = 3,56.10-8 mol/lVy tan ca AgCl gim i s ln sau khi axit ha dung dch ban u n khi c pH = 2,35 l:ln

IV. Bi tp tng hp chng kt ta v oxi ho-khphn ng oxi ha - kh xy ra.Ta c phn ng:

a) Nu khng c Cl- Phn ng (1) xy ra theo chiu thunCu 1: nh gi kh nng phn ng ca Cu vi Ag+ khi: a) Khng c Cl- b) C Cl- d Bit:

Phn ng (1) khng xy raTa c:Kt lun: Cu kh c Ag+ khi khng c Cl-Khi c mt Cl- d th phn ng gia Cu v Ag+ khng xy ra.b) C Cl-

Cu 3: Gi tr tch s tan (Ks) ca PbC2O4 250C l 8,5.10-10 v th kh chun ca cp Pb2+/Pb l E0=-0,126V. Tnh th in cc PbC2O4/Pb bng 2 cch.T (1) v (2) suy ra: Cch 1:

Cch 2:T (1), (2), (3), ta c:

Cu 1: (trch) Cho cc th chun sau y:

Trn c s hy tnh tch s tan ca AgBr 25oC.

BI TP T GiI

Cu 2: nh gi kh nng oxi ho kh ca cp Ag+/Ag khi c mt ion X- (X=Cl, Br, I, SCN).Hng dn: Tr li: .Tnh kh ca Ag tng ln, tnh oxi ho ca Ag+ gim xung.

Cu 3: nh gi kh nng phn ng gia Cu2+ v I-. Cho Ks(CuI)=10-12, Hng dn: Tr li: Cu2+ oxi ho d dng I- to ra I3- v CuI.

Cu 1: [99] (trch) Bc oxalat c tan trong nc l 2,06.10-4 ti pH = 7. tan ca n b nh hng khi c tc nhn to phc. Tnh tan ca bc oxalat trong dung dch cha 0,02M NH3 v c pH = 10,8. Bit vi s c mt ca amoniac th ion bc to thnh hai dng phc Ag(NH3)+ v Ag(NH3)2+. Cc hng s to phc tng nc tng ng l:V. Bi tp tng hp chng kt ta v phc cht

Dung dch c c mt ca amoniac v pH=10,8:Vy tan ca bc oxalat b nh hng bi pH v tc nhn to phc.

Cu 2: Trn 1,00 ml hn hp m (A) gm NH3 2,0 M v NH4NO3 2 M vi 1,00 ml dung dch B gm FeCl3 2,0.10-3 M v NaF 0,20 M. C kt ta Fe(OH)3 hay khng? Bit:Sau khi trn, ta c:- Trong dung dch B:

- Trong dung dch A:Ta c:Nh vy vn c kt ta Fe(OH)3.

Bi tp t giiCu 1: Bc clorua d dng ho tan trong dung dch amoniac v to ion phc:

Mt lt dung dch amoniac 1M ho tan c bao nhiu gam AgCl. Bit: KS(AgCl)=1,8.10-10, Tr li: mAgCl = 4,38 gamHng dn:

Cu 2: [99] Cadimi to thnh hyroxit hi kh tan l Cd(OH)2Hy tnh tan ca Cd(OH)2 trong nc nguyn cht.Tnh tan ca Cd(OH)2 trong nc c cha 10-3M ion CN- Bit: Cc hng s to phc tng nc ln lt l:Hng dn: a. Trong nc nguyn chtb. Trong nc c cha ion CN-: Vi:Tr li: a. S = 1,14.10-5M. b. S = 2,40.10-3M.

Cu 3: [99] Tnh tan ca AgCN trong dung dch nc bo ha AgCN, bit rng trong h c s hnh thnh cc phc xiano ca Ag+: Ag(CN)2-; Ag(CN)32-; Ag(CN)43-.Cc hng s to phc tng hp ln lt l:

VI. Bi tp tng hp chng oxi ha-kh v phc chtCu 1: [99] Tnh nng Cu2+ v Cd2+ khi lc mt mu Cd vi dung dch CuCl2 0,01M trong hn hp NH3 + NH4NO3 trong Cho:

Hn hp m NH3 + NH4NO3V 1 (1011,75) >> 2 (106,74) nn Cu2+ to phc hon ton.

T hp cc cn bng:

Tnh nng Cu2+ v Cd2+ theo cc cn bng

Cu 2: [99] C th ho tan hon ton 100mg bc kim loi trong 100ml dung dch amoniac nng 0,1M khi tip xc vi khng kh c khng?Cho bit nguyn t khi ca Ag = 107,88; hng s in li baz ca amoniac l Kb = 1,74.10-5; cc hng s bn ca phc [Ag(NH3)i]+ tng ng l: lg1 = 3,32(i = 1) v lg2 = 6,23(i = 2).Cc th kh (th oxy ha-kh) chun 25oC: Eo(Ag+/Ag) = 0,799V; Eo(O2/OH-) = 0,401V. p sut ring phn ca oxy trong khng kh l 0,2095atm. Phn ng c thc hin 25oC.

S mol cc i ca NH3 cn to phc l: 9,27.10-4 . 2 = 1,854.10-3(mol)

Nng tng cng ca Ag+ trong dung dch: [Ag+] = [Ag+] + [Ag(NH3)+] + [Ag(NH3)2+] = [Ag+].(1 + 1[NH3] + 2[NH3]2) = 1,58M Gi tr ny ln hn nhiu so vi lng Ag dng cho phn ng. Kt lun: C th ho tan hon ton 100mg bc kim loi trong 100ml dung dch amoniac nng 0,1M khi tip xc vi khng kh c khng

Cu 1: Co2+ c tnh kh rt yu, rt kh oxi ho thnh Co3+ trong mi trng axit, nhng khi c mt NH3 d th Co2+ d dng b oxi ho bi H2O2. Gii thch. Cho: Bi tp t giiHng dn:Tr li:

Cu 3: [99] nh gi kh nng ho tan ca Ag trong NH3 1M (khi khng c khng kh).Cho bit: Kb = 1,74.10-5; Eo(Ag+/Ag) = 0,799V; hng s Henri = 103,12; cc hng s bn ca phc [Ag(NH3)i]+ tng ng l: lg1 = 3,32(i = 1) v lg2 = 6,23(i = 2).Hng dn:Vi [OH-] t Kb. Tr li: [Ag(NH3)2+= 10-19,55. Ag khng tan trong NH3.

Cu 2: [99] Tnh hng s cn bng i vi phn ng sau:

Cho:

Hng dn:Tr li: K = 10-4,34.

C. KT LUN Trong phm vi ti, nhm em tp trung la chn v trnh by cc ni dung lin quan n bi tp tng hp v tnh ton cn bng. C th nh sau:- H thng ho cng thc tng qut lin quan n cn bng axit bazo, oxi ho kh, kt ta, to phc. - Su tm, phn loi v gii c 20 bi tp tng hp lin quan n mi phn. *- H thng bi tp t n gin n phc tp u c li gii, gip hc sinh, sinh vin t n tp, pht trin kh nng t hc.

D. TI LIU THAM KHO[1]. Olympic Ha hc cc Trng i hc Vit Nam ln th ba, 2005

p n phn Ho hc i Cng v V C, Bng A

*