7 Pin Dien Hoa Va the Dien Cuc

Chng VIII & IX

PIN IN HA & TH IN CC CHUN TH OXY HA KH

Ts. Phm Trn Nguyn Nguyn [email protected]

1. Phn ng oxy ha khPhn ng lin quan n s chuyn in t gia cc tiu phn ca phn ng

Ox1 + Kh 2 Ox1 + ne Kh1 Kh 2 Ox1 + ne Fe + e

Kh1 + Ox 2(bn phn ng kh) (bn phn ng oxy ha)

Ox = cht oxy ha nhn in t (b kh), lm gim s oxy ha 3+ 2+

Fe

Kh = cht kh cho in t (b oxy ha), lm tng s oxy ha

2I

I 2 + 2e

Cc cht ng vai tr oxy ha hay kh ty thuc vo th kh ca chng

2

Cu(s) + 2Ag+(aq)

Cu(s) + Zn2+(aq)

Cu2+(aq) + 2 Ag(s)

Khng p.ng

Cu/dd Ag+

Cu/dd Zn2+

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2. Cn bng phn ng oxy ha - kh

Sn +2 + Fe +3 Sn +2 ( Fe +3 + e Sn 2+ + 2Fe3+

Sn +4 + Fe +2 Sn +4 + 2eFe +2) x 2 Sn 4+ + 2Fe 2+

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2. Cn bng phn ng oxy ha - kh

Fe 2+ + MnO-4 MnO -4 + e- ?-1 = 1(x)Mn + 4(-2)O x = +8 - 1 = +7

Fe3+ + Mn 2+ Mn 2++2

MnO -4 + 5eMnO -4 + 5eMnO -4 + 5e- + 8H +(

Mn 2+ Mn 2+ + 4H 2 O Mn +2 + 4H 2 O (1)) x5

Fe 2+

Fe3+ + e

(2)5

5Fe2+ + MnO-4 + 8H +

5Fe3+ + Mn 2+ + 4H 2 O

Cn bng phn ng oxy ha - kh2Fe 2+ + Cr2 O 7 2Cr2 O7 + e- ?

Fe3+ + Cr 3+ Cr 3+

26Fe 2+ + Cr2 O7 + 14H +

6Fe3+ + 2Cr 3+ + 7H 2 O6

3. Chiu ca phn ng oxy ha- khMch in oxy ha-kh

Fe 2+ + Ce4+

Fe +3 + Ce3+ s di chuyn ca cc e- kt qa ca p. ha hc Hiu th o c gia 2 cc ca mch = hiu th oxy ha kh ca cc nguyn t to nn h = sc in ng ca pin Galvanic.-(PtI) Fe2+Fe3+Ce3+Ce4+(PtII)+

Fe2+ b oxy ha (in cc anode)

Ce4+ b kh (in cc cathode)

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Zn Zn2+ + 2e-

Cu2+ + 2e- Cu

- Zn(s) , Zn2+(aq) || Cu2+(aq) , Cu(s) +

Ecell = 1.103

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4. Th oxy ha- khin cc hydro chun (SHE) so snh kh nng oxy ha kh ca cc nguyn t v lp mch Galvanic gm cp cn kho st v in cc hydro chun in cc hydro chun (SHE) Pt|H2(g,1atm)| 2H+(a = 1) 2 H+ (a = 1) + 2e- H2 (g,1atm) Qui c: E = 0 V9

Th chunPt|H2(g, 1 atm), H+ (a = 1) || Cu2+(1 M), Cu(s) Ecell = ? cathode anode Ecell = Ecathode - Eanode Ecell = ECu2+/Cu - EH+/H2 0.340 V = ECu2+/Cu - 0 V ECu2+/Cu = +0.340 V H2 + Cu2+ H+ + Cu(s) Ecell = 0.340 V10

o th chun

anodeH2 2H+ + 2e-

cathodeCu2+ + 2e- Cu

cathode

anode

2H+ + 2e- H2 Zn Zn2+ + 2e-

E0Cu2+/Cu = 0,34 V

E0Zn2+/Zn = -0,763 V

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S mch Galvanic ca st clorua vi in cc hydro (Pt) H2, 2H+ || Fe2+, Fe3+ (Pt) hay SHE || Fe2+, Fe3+ (Pt) hiu s th trn cc cc ca mch galvanic = +0,771 V Gi tr dng ch tnh oxy ha ca Fe3+ > H+ th o c vi in cc hydro chun khi nng ca cc ion = 1M, nhit 250C gi l th chun (E0) Th in cc cng dng tnh oxy ha ca tc nhn oxy ha cng mnh, v dng kh ca n c tnh kh cng yu

Ce 4+ + e Zn 2+ + 2e

Ce3+ E 0 = 1,61V Zn E 0 = 0,76V12

Ce4+ l tc nhn oxy ha mnh, Ce3+ tc nhn kh yu Zn2+ l tc nhn oxy ha yu, Zn tc nhn kh mnh

TH CHUNBn phn ng F2 + 2e- 2FTc nhn Tc nhn MnO4- + 5e- Mn2+ Oxy ha kh Ce4+ + e- Ce3+ (in HCl) O2 + 4H+ + 4e- 2H2O Ag+ + e- Ag(s) Cu2+ + 2e- Cu(s) 2H+ + 2e- H2(g) Cd2+ + 2e- Cd(s) Fe2+ + 2e- Fe(s) Zn2+ + 2e- Zn(s) Al3+ + 3e- Al(s) K+ + e- K(s) Li+ + e- Li(s) Tnh oxy ha tng Tnh kh tng Eo (V) 2.890 1.507 1.280 1.229 0.799 0.339 0.000 -0.402 -0.440 -0.763 -1.659 -2.936 -3.040

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Sc in ng ca pin- (PtI) Sn2+, Sn4+ Fe3+, Fe2+(PtII) + anode cathode0 Sn 4+ + 2e- Sn 2+ , E Sn 4+ /Sn 2+ = 0,154 Fe3+ + e - Fe 2+ , E 0 3+ /Fe2+ = 0, 771 Fe

Anode: Xy ra qu trnh oxy ha cht kh mnh (bn tri) Cathode: Xy ra qu trnh kh cht oxyha mnh (bn phi)

E pin = E right E left = E cathode E anode = E + E 0 E pin = E 0 3+ /Fe2+ ESn 4+ /Sn 2+ Fe= 0, 771 0,154 = 0, 61714

* Khi pin c thit lp, s ca pin lun dng

Tnh sc in ng ca pin c thit lp t 2 bn pin sau

Fe3+ + e I3 + 2e vi E 0 3+ /Fe2+ > E 0 - /IFe I3

Fe 2+ E 0 = 0,771V 3I- E 0 = 0,5355V

E pin = E 0 3+ /Fe2+ E 0- /I- = 0, 771 0,536 = 0, 235 Fe I3

2Fe3+ + 3I- = 2Fe 2+ + I3

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5. Phng trnh NERNSTBn phn ng: aOx + ne- bKh Th ca bn pin ( 25 oC), E, c tnh nh sau:a RT [ Ox ] E=E + ln nF [ Kh ] a O

[ Ox ] a 0.05916 O E=E + log [ Kh ] b n

Eo = th in cc chun R = hng s kh = 8.314 J/K-mol T = nhit tuyt i (298K) F = hng s Faraday = 9.649 x 104 C/mol n = s in t

Mt dd gm Cr2O72- 10-3M v Cr3+ 10-2M. Tnh th ca bn pin trong mi trng acid pH = 22Cr2 O7 + 14H + + 6e

E = E Cr2O2-/Cr3+07

[Cr O2- ][H + ]14 0.05916 2 7 = 1.06V + log 3+ 2 6 Cr

2Cr 3+ + 7H 2 O

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5. Phng trnh NERNSTXt ton b phn ng: Th ca ton phn ng

n2 Ox1 + n1 Kh2 n1Ox 2 + n2 Kh1 0 0 0 E pin = E + E - & E pin = E + E E pin = (E 0 E 0 ) + 0.05916 [Ox 2 ]n1 [Kh1 ]n2 0.059 lg lg Q = E0 n2 n1 [Ox1 ] [Kh 2 ] n1n2 n1n2

Cho pin Cu Fe iu kin chun (nng = 1M) Cu2+ + 2e- Cu(s) 0.339 V 2+ + 2e- Fe(s) -0.440 V Fe Phn ng Galvanic Cu2+(aq) + Fe(s) Cu(s) + Fe2+(aq) Fe|Fe2+(1M) || Cu2+(1 M)|Cu

E 0 = E 0 E 0 = 0,339 + 0, 440 = 0, 779V pin +

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p dng phng trnh Nernst tnh s ca pin sau, Epin. (Pt) Fe2+(0.10 M),Fe3+(0.20 M)||Ag+(1.0 M)|Ag(s) Fe2+(aq) + Ag+(aq) Fe3+(aq) + Ag (s) Epin = Epin Epin = Epin 0.05916 log Q n

0.05916 [Fe3+] log 2+ [Fe ] [Ag+] n

E0pin = 0.799 V 0.771 V = 0.0280 Epin = 0.028 V 0.018 V = 0.010 V18

5. Phng trnh NERNSTPhn ng Galvanic Fe|Fe2+ (1M) || Cu2+ (1M)|Cu Cu2+(aq) + Fe(s) Cu(s) + Fe2+(aq) Epin = 0.779 V E > 0 p.ng ca pin xy ra t nhin theo chiu thun E < 0 p.ng ca pin xy ra t nhin theo chiu nghch Nu pin chy trong thi gian di: Cht p.ng b tiu th Sn phm c hnh thnh P.ng t n cn bng Epin 0 : l do ht pin E = 0 p.ng ca pin t cn bng19

5. Phng trnh NERNST- Th cn bngKhi pin t n cn bng ( 250C) : Epin = 0E pin = (E 0 E 0 ) + 0.05916 [Ox 2 ]n1 [Kh1 ]n2 0.05916 lg lg Q = 0 = E0 n2 n1 [Ox1 ] [Kh 2 ] n1n2 n1n2

E pin = E 0

0.05916 lg K = 0 n1n2

K = 10 E0 > 0: K > 1 E0 < 0: K < 1

n1n 2 E o /0.05916

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Mi quan h gia nhit ng hc (G0), cn bng (Kcb) v in ha hc Kcb o thnh phn cb

G 0 = RT lnK eqHG0 =H-TS0S0G0

E0 = pin

RT lnK eq nF

G 0 = nFE 0 pin

Epin

E0 , E0 pin

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6. in cc so snh (Reference Electrode)in cc bc (Ag/AgCl) bo ha bng dd KCl AgCl(s) + e- Ag (s) + Cl E = +0.197 V in cc calomel (SCE) bo ha bng dd KCl Hg2Cl2 + e- Hg + Cl E = +0.241 V

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6. in cc so snhEo = Eo - 0.241 (SCE) Eo = Eo - 0.197 (Ag/AgCl) Eo(SHE) Cu2+ + 2e- Cu(s) Fe2+ + 2e- Fe(s 0.339 V -0.440 V E(SCE) 0.098 V -0.681 V E(Ag/AgCl) 0.142 V -0.637 V

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7. Chun oxy ha khXy dng th biu din s thay i th oxy ha kh E ca dung dch nh phn theo mc thm dd chun ca cht oxy ha hay kh Xy dng ng cong chun th ca 100,0 mL dd Fe+2 0,100M vi 10,0mL; 50,0mL; 100mL, 200,0mL dd Ce+4 0,100M trong mi trng acid HNO3.

Fe 2+ + Ce 4+ Ce3+ + Fe3+ E 0 3+ /Fe2+ = 0,771V Fe

E 0 4+ /Ce3+ = 1,61V Ce

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Xy dng ng cong chun th ca 100,0 mL dd Fe+2 0,100M vi 10,0mL; 50,0mL; 100mL, 200,0mL dd Ce+4 0,100M trong mi trng acid HNO3. Phn ng chun :

Fe 2+ + Ce 4+

Ce3+ + Fe3+

Thm V =10,0 mL Ce4+

VFe2+ M Fe2+ > VCe4+ M Ce4+

# mmol Ce4+ thm vo = 0,100M x 10,0 mL = 1.00 mmol # mmol Fe3+ to thnh = 1.00 mmol # mmol Fe2+ cn li = (0,100 M x 100,0 mL)-1,00 mmol = 9,00

E=E

0 Fe3+ / Fe 2+

0, 0592 [Fe3+ ] + log n [Fe2+ ]25

E = 0, 771 + 0, 0592 log(1, 00 / 9, 00) = 0, 714V


Fe 2+ + Ce 4+

Ce3+ + Fe3+

Thm V =50,0 mL Ce4+

VFe2+ M Fe2+ > VCe4+ M Ce4+

# mmol Ce4+ thm vo = 0,100M x 50,0 mL = 5.00 mmol # mmol Fe3+ to thnh = 5.00 mmol # mmol Fe2+ cn li = (0,100 M x 100,0 mL)-5,00 mmol = 5,00

E = E 0 3+ / Fe2+ + Fe

0, 0592 [Fe3+ ] log n [Fe2+ ] 5, 00 E = 0, 771 + 0, 0592 log = 0, 771V 5, 00

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Fe 2+ + Ce 4+

Ce3+ + Fe3+

Thm V =100,0 mL Ce4+ im tng ng

VFe2+ M Fe2+ = VCe4+ M Ce4+

# mmol Ce4+ thm vo = 0,100M x 100,0 mL = 10,0 mmol # mmol Fe3+ cb = 10,0 x ~ 10,0 # mmol Fe2+ cb = x # mmol Ce3+ cb = 10,0 x ~ 10,0 # mmol Ce4+ cb = x27


Fe 2+ + Ce 4+

Ce3+ + Fe3+



E Fe3+ /Fe2+ = E Ce4+ /Ce3+

E 0 3+ / Fe2+ + Fe E0 Fe3+ /Fe2+

0, 0592 [Fe3+ ] 0, 0592 [Ce 4+ ] = E 0 4+ /Ce3+ + log log Ce n n [Fe 2+ ] [Ce3+ ] 0, 0592 [Fe3+ ] [Ce3+ ] = = 0, 0592 log K cb log 1 [Fe 2+ ] [Ce 4+ ]28

E

0 Ce4+ /Ce3+

K cb = 1, 7 x1014

Xy dng ng cong chun th ca 100,0 mL dd Fe+2 0,100M vi 10,0mL; 50,0mL; 100mL, 200,0mL dd Ce+4 0,100M trong mi trng acid HNO3. Phn ng chun : im tng ng14

Fe 2+ + Ce 4+

Ce3+ + Fe3+

Thm V =100,0 mL Ce4+


E Fe3+ /Fe2+ = E Ce4+ /Ce3+

[Fe3+ ] [Ce3+ ] (10, 0)(10, 0) K cb = 1, 7 x10 = = [Fe 2+ ] [Ce 4+ ] ( x)( x)x = 7, 7 x107 mmol Fe 2+ = mmol Ce 4+

E = E 0 3+ / Fe2+ + 0, 0592 log[Fe3+ ] /[Fe2+ ] = Fe = 0, 771 + 0, 0592 log(10, 0 / 7, 7x107 ) = 1,19V29


Fe 2+ + Ce 4+

Ce3+ + Fe3+



E cb = E Fe3+ /Fe2+ = E Ce4+ /Ce3+

E cb = E E cb = E2E cb = (E

0 Fe3+ /Fe2+

[Fe3+ ] + 0, 0592 log [Fe 2+ ] [Ce 4+ ] + 0, 0592 log [Ce3+ ]0 Ce4+ /Ce3+

0 Ce4+ /Ce3+

0 Fe3+ /Fe2+

+E

[Fe3+ ][Ce3+ ] ) 0, 0592 log [Fe 2+ ][Ce 4+ ]

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Fe 2+ + Ce 4+

Ce3+ + Fe3+



E cb = E Fe3+ /Fe2+ = E Ce4+ /Ce3+ [Fe3+ ][Ce3+ ] ) 0, 0592 log [Fe 2+ ][Ce 4+ ]

2E cb = (ETi cb

0 Fe3+ /Fe2+

+E

0 Ce4+ /Ce3+

[Fe3+ ] = [Ce 4+ ] & [Ce3+ ] = [Fe 2+ ]

1 E cb = (E 0 3+ /Fe2+ + E 0 4+ /Ce3+ ) = 1,19V Ce 2 Fe

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Fe 2+ + Ce 4+

Ce3+ + Fe3+

Thm V = 200,0 mL Ce4+ VFe2+ M Fe2+ < VCe4+ M Ce4+ # mmol Ce4+ thm vo = 0,100M x 200,0 mL = 20.0 mmol # mmol Ce4+ d = 20,0 -(0,100 M x 100,0 mL) = 10,0 mmol # mmol Ce3+ to thnh = 10,0 mmol

E = E Ce4+ / Ce3+ +

0, 0592 [Ce 4+ ] log n [Ce3+ ] 10, 0 E = 1, 61 + 0, 0592 log = 1, 61V 10, 0

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Tnh th ti im tng ng ca qu trnh chun 100,0 mL dd Fe+2 trong dd H2SO4 0,500M bng 100,0 mL dd MnO4- 0,0200 M. Phn ng chun :

5Fe2+ + MnO-4 + 8H +E 0 4+ / Fe3+ Fe4

5Fe3+ + Mn 2+ + 4H 2 O

= 0, 771V

E 0 2+ / MnO = 1, 51V Mn

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8. Cch nhn ra im tng ng trong pp Oxy ha khT ch th Chuyn mu do dung dch gy ra do lng d ca dd chun Vi d: Chun KMnO4 (mu tm) Ch th h tinh bt Vi d: Chun Iod, ho tinh bt to phc vi I2 xanh m Ch th oxy ha kh Cht c mu thay i tu thuc vo th oxy ha kh

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7 Pin Dien Hoa Va the Dien Cuc

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