Chuong3 Oxy Hoa-khu

7/23/2019 Chuong3 Oxy Hoa-khu

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07/09/20

CHNG 3

PHN NGOXY HA-KH

PHN NG OXY HA KH

I. MT S KHI NIM V PHN NG OXH-K

II. CC YU T NH HNG N TNH OXH-K CA

CC CHT

III. NH GI KH NNG THAM GIA PHN NG OXH-

K CA CC CHT.

IV. S N NH CA CC CHT OXY HO V KH

TRONG MI TRNG NC.

PHN NG OXY HA KH

1. nh ngha phn ng oxy ho kh

2. Cp oxy ho kh lin hp.

a. nh ngha.

b. S tng ng gia phn ng oxy ho kh v phn ng

axit - base

3. Cn bng phn ng oxy ho kh

4. Phn ng oxy ho kh v qu trnh in cc

a. Phn ng in ho

b. Phn ng in cc v phng trnh Nernts

a. nh ngha

nhngha: Phnngoxy ha-khl phnngtrong cschuynvnelectron tchtkhsang chtoxy ha dnnlm thay isoxy ha cacc nguyn tngvai tr chtoxy ha v chtkh

Xt Phnng: aOXH1+ bKh2cKh1+ dOXH2 (1)

Qu trnh kh: aOXH1+ ne cKh1

Qu trnh oxy ha: bKh2nedOXH

2

Cc chtoxy ha v khtrong mibnphnngtothnh mtcpOXH - K lin hp.

Hngscnbngcaphnng(1):ba

dc

cb

KhOXH

OXHKhK

][][

][][

21

21

NH NGHA


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b. S tng ng gia phn ng oxy ha - kh v phn ng axit baz Phnngaxitbaz:

- nH+

aAx1+ bBaz2cBaz1+ dAx2

+ nH+

Phnngoxy ha - kh:

+ne

aOXH1+ bKh2cKh1+ dOXH2

-ne

0

/ KhOXH

Ka, Kb

NH NGHA

P OXH K: Cht kh - e trc tip cho cht OXH.

P in ha: cc cht OXH v kh trao i electron vi cc incc tng ng.

1 p OXH K1 qu trnh in cc

P OXH K thunqt trong ngt Ganv:

qu trnh t din ra,

ha nng in nng.

E = +- -.

P OXH Knghchqt trongbnh in phn:

qt cng bc

in nng ha nng.

Engoai > - EGanv.

NH NGHA

Phng trnh Nernst:

Quy c v du ca (theo chu M): ni ln KN xy ra ca qtin cc. G = - nFE

Phn ng c xt l phn ng kh.

Nu qt kh xy ra trn in cc: > 0.

Nu qt kh khng xy ra trn in cc): < 0.

V d: Zn2++ 2e Zn 0= -0.763V

Cu2++ 2e Cu 0= +0.337V

: tnh OXH ; tnh kh

Kh

OXH

nF

RTln0

Kh

OXH

nlg

059.00 V d:

Al + CuSO4Al2(SO4)3+ Cu

Al -3e Al+3

Cu+2+ 2e Cu

2Al + 3Cu+2= 2Al+3+ 3Cu

2Al + 3CuSO42Al2(SO4)3+ 3Cu

2

3

CN BNG PHN NG OXY HA KH


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V d:

O2

H4

SO2

K3

KNO4

MnSO4

SO2

H2

KNO4

KMnO

32

2

4

NO2eNO

Mn5eMnO

O4HMn8H5eMnO 22

4

2HNOOH2eNO 322

O3H5NO2Mn6H5NO2MnO 2324

2

5

O3HSOK5KNO2MnSOSO3H5KNO2KMnO 242344224


V d:

OHKClCrOKKOHCrClKClO 24233

OHClOHeClO 636 23

OHCrOOHeCr 22

4

3 483

OHCrOClOHCrClO 22

43

3 52102

OHCrOKKClKOHCrClKClO 24233 527102


KOHKNOMnOOHKNOKMnO 32224

OHMnOOHeMnO 423 224

HNOOHeNO 22 322

6H8OH3NO2MnOO7H3NO2MnO 32224 OHNOMnOOHNOMnO 23232 32224

KOHKNOMnOOHKNOKMnO 23232 32224


nh gi kh nng tham gia phn ng oxy ha

kh ca cc cht:

- S dng cc hm nhit ng.

- Th kh v phng trnh Nerst.

- Gin Latimer.

- Gin Frost.

KH NNG THAM GIA PHN NG


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CC YU T NH HNG N TNH OXH-K:

Kh nng oxy ha kh ca cht ph thuc cc yu tsau:

c im cu to lp v electron v trng thi oxyha ca nguyn t

bnvngcacht.

Mi trng tin hnh phn ng.

KH NNG THAM GIA PHN NG

NGUYN TC XC NH S OXH BN CA

NGUYN T

a) S oxy ho khng

b) Cc nguyn t h s

c) Cc nguyn t h p

d) Cc nguyn t h d

e) Cc nguyn t h f

f) Quy tc

S OXY HO KHNG:

Kim loimnhv phi kim mnhc mcOXH khng

kmbn

Kim loi cng yu, phi kim cng yu: mc OXH

khng cngbn.

Cc nguyn tlngtnh uc mcOXH khngbn

NGUYN TC XC NH S OXH BN CANGUYN T b. Cc nguyn t h s

Cc nguyn ths:

Cc nguyn ths chc mtsOXH dngbnvng

trng visthtcaphn nhm.

V d: Na(IA) c sOXHbn+1; Ca(IIA) c sOXH

bn+2

Ring H c hai sOXH +1 v -1 nhngsOXH +1 l

bnvnghnhn sOXH -1.

NGUYN TC XC NH S OXH BN CANGUYN T


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c. Cc nguyn t h p

Cc nguyn thp:

Quy tcchnlcaMendeleev.

Cc mcoxi ha c cuhnh bo ha mtlp(ns2np6)

hocmtphn lp(ns2)bnhnhn.

Trong mtchu kttri quaphisoxi ha dng

cao nhtcacc nguyn tkmbndn(v rt d

ly li e mt do mt in tch dng tng

dn v r gim dn).

nhluttunhon thcp


NGUYN T QUY TC CHN L CA MENDELEEV

Cc nguyn thp:

Nguyn t phn nhm chn c cc s OXH chn bn hn

cc s OXH l.

Nguyn t phn nhm l c cc s OXH l bn hn cc s

OXH chn.

V d: Cl (VIIA) c cc s OXH -1, +1, +3, +5, +7 bn

hn cc s OXH chn.

S (VIA) c cc s oxy ha -2, +2, +4, +6 bn hn cc s

OXH l.

Xe (VIIIA) hinchbitcc hpchtc soxy ha +2,+4, +6 v +8.

V d:

Cl c cc mc oxy ho bn hn: -1 (cu hnh Ar) v +7 (Ne),

v +5 v s dng ht 5 e phn lp 3p.

S c cc mc oxy ha bn hn: -2 (cu hnh Ar), +6 (Ne) v

+4 v s dng ht 4 e phn lp 3p.

QUY TC CHN L CA MENDELEEV

V d: Xt dy chu kIII (Al, Si, P, S v Cl)Al: Mc OXH + 3 rt bn vng, nhm trong cc hp cht iu kin thng u c s OXH +3.

Si: Mc OXH +4 rt bn vng (nh Al).

P: ion PO43-kh bn, nhng khng c tnh OXH d trong

mi trng acid m c.

H3PO4+ 2H+

+2e = H3PO3 + H2O, o

= -0.276V, pH = 0PO4

3-+ 2H2O + 2e = HPO43- + 3OH-, o = -1.12V, pH = 14

QUY TC CHN L CA MENDELEEV


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S: ion SO42-khng c tnh oxy ha trong mi trngkim,

c tnh oxy ho rt yu mi trng acid (pH = 0) v lchtOXH kh mnhkhi l acid sulfuric nguyn cht (oxyha cbc).

SO42-+ 4H++ 2e = H2SO3 + H2O, o = 0.17V, pH = 0

SO42-+ H2O + 2e = SO3

2-+ 2OH

-, o = -0.93V,pH =14

Cl: Hpcht+7 caCl l chtoxy ha mnh. ClO4-l chtoxy ha mnhpH = 0, HClO4nkhi tipxc cc chthuc hoc khi b chiu sng. Tnh oxy ha yu trong mitrngkim.

ClO4-+ 2H++ 2e = ClO3

-+ H2O, o = 1.19V, pH = 0

ClO4-+ H2O + 2e = ClO3-+ 2OH-, o = 0.36V, pH =14

QUY TC CHN L CA MENDELEEVd. Cc nguyn t h d

Cc nguyn thd:

Trong mtchu kttri quaphicc mcoxi ha dngcao

nhtkmbnvngdn.

ivicc ng. td sm, ttccc e uc ththam gia

tolin kt

ivicc ngtd mun, chmtse (n - 1)d tham gia to

lin kt

Trong hp cht, nguyn t ca nguyn t d c th cha

electron (n-1)d c thn.

Trong mtphn nhm ttrn xungcc mcoxi ha dng

cao nhtbnvngdn. Mcoxi habnnhtcacc nguyn thf l +2


NGUYN T

NH LUT TUN HON TH CP

Trong mt phn nhm chnh: s oxyha dng cao nht cachu k IV km bn r rt so vi s oxy ha dng cao nht canguyn t chu k III; s oxy ha dng cao nht ca chu k VIkm bn r rt so vi s oxy ha dng cao nht ca nguyn tchu k V.

V d1: Xt phn nhm VIIA.

Xt trong cng iu kin ion BrO4-oxy ha mnh hn hn

ion ClO4-:

ClO4-+ 2H++ 2e = ClO3

-+ H2O, o = 1.19V, pH = 0

BrO4-+ 2H++ 2e = BrO3

-+ H2O, o = 1.763V,pH = 0

Hp cht cha At s oxy ha +7 khng tn ti trong dung dch

nc v n l cht oxy ha qu mnh, oxy ha nc gii phng

kh oxy, trong khi hp cht ca I+7tn ti trong dung dch.

H5IO6+ H++2e= IO3

-+3H2O, o = 1.64V, pH = 0

V d2: Xt phn nhm IVA.

Hp cht cha Si+4rt bn, khng c tnh oxy ha ngay trong mi

trng acid rt mnh, n hu nh khng b kh trong dung dchnc.

Ge+4cng khng c tnh oxy ha trong mi trng acid (pH=0)

nhng rt d b kh v s oxy ha +2.

GeO2(r) +2H++2e= GeO(r) +H2O, o=-0.12V,pH=0



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SnO2khng th hin tnh oxy ha pH=0 trong khi PbO2l

cht oxy ho rt mnh trong cng iu kin.

SnO2(r) +2H++2e= SnO(r) +H2O, o=-0.088V,pH=0

PbO2(r) +4H++2e= Pb2++2H2O, o= 1.445V,pH=0.

V d 3: xt th kh cc hp cht (V) phn nhm VA

H3PO4 + 2H+ + 2e = H3PO3 + H2O - 0,276

H3AsO4 + 2H+ + 2e = HAsO2 + 2H2O +0,56

Sb2O5 (r) + 6H+ + 2e = 2SbO+ + 3H2O +0,58

NaBiO3(r) + 4H+ + 2e = BiO+ + Na+ + 2H2O > +1,8


Giithch:

Quy luttunhon thcpdo vicxuthinlnutin cc phn

lp(n-1)d (chu kIV) v (n-2)f (chu kVI) lm cpelectron ns

km hotnghndnntngtngtskm bnvngcamc

oxy ha dngcao nhtcacc nguyn tthuccc chu kny so

vicc nguyn tthucchu ktrc.

Bang so sanh the khu

-50

0

50

100

150

200

P As Sb Bi

Series1


Trong mt phn nhm ph t trn xung di mc

oxy ha cao nht bn dn.

V d: trong mi trng acid, phn nhm VIB:

Bnphnngkh 0(V)

Cr2O72-+ 14H++ 4e 2Cr4++ 7H2O +0,95

MoO42-+ 4H++ 2e MoO2 + 2H2O +0,606


V d 2: Xt phn nhm IVB, da vo th oxy ho kh, thy r

Hf(+4) v Zr(+4) bn hn r rt so vi Ti(+4).

TiO2++ 2H++e = Ti3++H2O, o=0.1V,pH=0

ZrO2++ 2H++4e = Zr+H2O, o=-1.5V,pH=0

HfO2++ 2H++4e = Hf+H2O, o=-1.7V,pH=0

V d 3: Xt phn nhm VIB, da vo th oxy ha kh, thy r

Mo(+6) v W(+6) bn r rt hn so vi Cr(+6). Cr2O7

2-+ 14H++6e = 2Cr3++7H2O, o=1.33V,pH=0

MoO22++e = MoO2

+ o=+0.48V

WO3(r)+ 2H++2e = W2O5(r) +H2O, o=-0.03V,pH=0



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V d 1: S oxy ha cao nht hin bit n ca cc nguyn t d

chu k 4:

V d2: Cuhnh electron caion Cr3+trong Cr2O3l (n-1)d3

IIIB IVB VB VIB VIIB VIIIB IB IIB

Sc Ti V Cr Mn Fe Co Ni Cu Zn

+3 +4 +5 +6 +7 +6 +5 +5 +5 +2

NH LUT TUN HON TH CP Trong mt chu k t tri qua phi cc mc oxy ha dng cao

km bn vng dn.

V d1: Xt chu kIII: Ti(4), V(5), Cr(6), Mn(7), Fe(8),

Co(9), Ni(10), Cu(11) (trong ngocl tngse trn 3d4s).

TiO2+ + 2H+ + e = Ti3++ H2O, o = 0.1V, pH = 0

VO43- + 6H+ + 2e = VO++3H2O, o = 1.26V, pH = 0

Cr2O72- + 14H+ + 6e = 2Cr3+ +7H2O, o = 1.33V, pH = 0

MnO4- + 8H+ + 5e = Mn2+ + 4H2O, o = 1.51V, pH = 0


Cha tm thy hp cht Fe+8.

FeO42-+ 8H++3e = Fe3+ + 4H2O, o > 1.9V, pH = 0

Chatm thyhpchtCo+9, hinchbitncc hpchtCo

n+6. Chc cc hpchtCo+3tntitrong dung dchncv

chng cngoxy ha cnc. Co3++ e = Co2+, o = 1.84V,

pH = 0.

Ni tng tCo, ion Ni3+khng th tn ti tdo trong dung

dchnc,v vyhpchtbncaNi lun mc+2.

Cu cng tng t Ni v Co, trong iu kin thng ch bit

n Cu (+1,+2).

NH LUT TUN HON TH CP QUY TC CHUNG

Cc nguyn t mc oxy ha trung gian c th ng vai tr

cht oxy ha khi tc dng vi cht kh hay ng vai tr cht

kh khi tc dng vi cht oxy ha. Tuy nhin tnh cht c

trng ca nguyn t ph thuc vo bn vng ca cc

mc oxy ha c trng ln cn vi n.

VD: Xt Cl(+5), c tnh oxy ho v c Cl(+7) v Cl(0) u c

tnh oxy ha.

Xt cc hp cht S(+4): V S(+6) kh bn vng v hu nh

khng th hin tnh oxy ha, nn S+4c tnh kh. Mt khc S+4

c tnh oxy ha yu v S(0) c tnh kh yu.


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Nguyn t mc oxy ha km bn c xu hng chuyn v mc oxy

ha bn. Nu mc oxy ha bn cao hn mc oxy ha km bn th cht c

tnh kh c trng. Nu mc oxy ha bn thp hn mc oxy ha km

bn th cht c tnh oxy ha c trng. Nu mc oxy ha km bn ca

nguyn t nm gia hai mc oxy ha bn hn th cht c c tnh oxy ha

v tnh kh l c trng.

V d : H2S c tnh kh c trng v mc oxy ha 0 ca S kh bn hn

mc oxy ha 2.

HClO l cht oxy ha c trng v mc oxy ha bn ca Cl l 1.

Na2SO3c tnh kh v tnh oxy ha c trng v mc oxy ha +6 v

0 ca S c trng hn mc oxy ha +4.

Quy tc so snh tm tnh oxy ha kh c trng

Nng lng lin kt trong phn t cng cao th kh nng hot

ng ha hc cng thp.

V d 1: Oxy c m in 3,44 cn Clor c m in 3,16

nhng iu kin thng, kh Clor l mt cht oxy ha rt

mnh lit cn oxy l cht oxy ha m du. Nguyn nhn l do

O2c nng lng lin kt (493 kJ/mol) ln hn hn nng lng

lin kt trong phn t Cl2(239 kJ/mol).

BN VNG CA CHT

Ion nm trong hp cht trng thi rn hot ng ha hc km

hn khi nm trong trng thi t do:

V d: Th kh ca ion Pb4+(aq) ln hn hn PbO2

PbO2(r) + 2H+(aq) + 2e- = Pb2+(aq) + 2H2O o= +1,449V

Pb4+(aq) + 2e- = Pb2+(aq) o= +1,694V

Tm li, hp cht cng bn vng th kh nng hot ng ha hc

cng km.

BN VNG CA CHT NH HNG CA MI TRNG PHN NG

i vi rt nhiu phn ng, mi trng acid lm tng mnh

tnh oxy ha ca cht oxy ha v mi trng base lm tng

mnh tnh kh ca cht kh.

Trong trng hp ny, khi nim acid base hiu theo ngha

tng qut nht.

a) nh hng ca Acid base BronstedLawry n tnh oxy

ha kh: V d 1: Th kh ca ion SO42-tng nhanh khi chuyn t mi

trng base sang mi trng acid:

pH = 0 : SO42-+ 2H++ 2e- = H2SO3+ H2O o= +0,17V

pH = 14: SO42-+H2O + 2e- = SO3

2-+ H2O o= -0,93V


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b) Anh hng ca acid base Lewis:

V d: Ion Ag+.aq l mt cht oxy ha trung bnh yu trong dungdch nc: Ag+ + e- = Ag o= +0,799V

Tuy nhin khi c mt base Lewis CN-th n li th hin tnh kh yu:Ag(CN)2

- + e- = Ag + 2CN- o= -0,29V

c) Anh hng ca acid base Usanovich.

Khi hon nguyn phospho t qung phosphorit 15000C, trong thnhphn phi liu c ct. Ct ng vai tr acid Usanovic lm tng tnh oxyha ca P(V):

2Ca3(PO4)2 + 10C + 6SiO2 = 6CaSiO3 + 10CO + P4

Trong phn ng ny SiO2tc dng vi photphorit to calcisilicat, giiphng phospho oxide.

(Xem file Kh qung phosphorit)

NH HNG CA MI TRNG PHN NG Trong mi trng c mt ion to hp cht ion t tan cng lm

thay i tnh oxy ha kh ca cht:

V d: Tnh oxy ha ca ion Cu2+tng ln r rt khi c mt

ion Cl-do CuCl l cht t tan (TCuCl = 1,2.10-6)

Cu2+ + e- = Cu+ o= +0,153V

Cu2+ + Cl- + e- = CuCl(r) o= +0,538V

Trong trng hp nng ion cloride cao th ng (I) cloride

tan ra v to thnhphc [CuCl2]-c Kkb= 10-5,35

Cu2++ 2Cl-+ e- = [CuCl2]- o= +0,4633V)

NH HNG CA MI TRNG PHN NG

S DNG CC HM NHIT NG HA HC

Cn c vo i lng bin thin th ng p tiu chun

ca phn ng, chng ta c th nh gi v kh nng xy

ra phn ng v phng din nhit ng. i vi phn

ng nhit phng, c th cn c vo gi tr nhit phn

ng, cn phn ng nhit cao cn c vo i lng

bin thin entropy phn ng. Cch xem xt tng t nh

i vi phn ng khng thay i s oxy ha.

Cn nhn mnh rng a s phn ng d pha ca v c u

c c ch phc tp, do lun cn kho st ng hc khi

ng dng cc phn ng ny.

TH KH - PHNG TRNH NERNST

Th kh cho bit mnh ca cht oxy ha v cht

kh lin hp vi n. Th kh cng ln, cht oxy ha

cng mnh v cht kh lin hp cng yu v ngc li.

V d: Th oxy ha kh ca cp Au3+/Au trong mi

trng acid = +1,68V cho bit Au3+l cht oxy ha rt

mnh , ngc li Au l cht kh ht sc yu (Vng lkim loi rt bn vng).


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3. GIN LATIMERTh Oxy ha-Kh ca cc bn

phnngring lchthuntinkhi

thnh lp pin hay trong cc qu

trnh phn tch. Nhngkhost

mtqu trnh chuynha oxy ha-

kh phc tp th li kh khn.

Trong trnghpny Latimer a

ra gin mang tn ng biu

dincc qu trnhphctp.

Lewis H. Latimer

TH KH - PHNG TRNH NERNST GIN LATIMER

Datrn cc ktqu: G = -nFE, v trong chuiphnngGT= Gi.

V d: Xt trng hp ca Fe.

Bnphnng E0 = -nFE0

Fe2++2e Fe -0.44V -2F0.44

Fe3++e Fe2+ 0.771V -1 F 0.771

Fe3++3e Fe E0T0.331V -3FE0T

T ta c E0

T= -0.036V3

0

22

0

110

3n

EnEnE

V d thit lp gin Latimer cho Iode

-535.

2

430.1154.1-

3

589.1-

4 IIHOIIOIO (+7) (+5) (+1) (0) (-1)

OHIO2eIO2H 2-

3

-

4

OH2HOI4eIO5H 2-

3

OH3HOI6eIO7H 2-

4

FEnFEnFEn o33o

22

o

11 E6

4E2E o3

o

2

o

1

1.299

1.2996

1.15441.5892

GGG o3

o

2

o

1

G

G

G

o

3

o

2

o

1

GIN LATIMER

Biu din gin Latimer

Cc dng hp cht ca nguyn t c sp xp theo

chiu gim dn s oxy ha.

Ni gia cc dng ny l mi tn km theo gi tr th

oxy ha-kh ca qu trnh tng ng.

Trn nguyn tc, thO-Kphigimttri sangphi. Nu nguyn tc ny b vi phm (dng sau c th ln

hn dng trc), th dng sau s khng bn vng,

rt d b d ly, to 2 dng ln cn ca n.

GIN LATIMER
http://images.google.com.vn/imgres?imgurl=http://www.energyquest.ca.gov/scientists/images/latimer.jpg&imgrefurl=http://www.energyquest.ca.gov/scientists/latimer.html&h=200&w=160&sz=8&hl=en&start=0&tbnid=Ui3BwZaElaeTzM:&tbnh=104&tbnw=83&prev=/images?q=latimer&gbv=2&svnum=10&hl=en


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V d 1: Gin Latimer ca Fe biu din nh sau.

V d 2: Gin Latimer ca Mn trong mi trng acidv base.

D ly

GIN LATIMER

Cc yu t nh hng n th O-K, dy Latimer

Tng qut, cc yu t lm thay i G (G = -nFE) u nh

hng n th O-K (E0hay 0).

Cc yu t ny l:o 1/ Nng .

o 2/ Nhit .

o 3/ Cc tc cht khc (khng phi kh tr).

o 4/ pH (trng hp ring ca trng hp 3).

][

][lg

059.000

Kh

Ox

n

Kh

Ox

a

a

nF

RTln0

Hay c th vidung dch nc 250C th

GIN LATIMER

Kho st yu t pH. Vi ClO4-, trong mi trng acid v base ta cth O-K nh sau:

ClO4-+ 2H++ 2e = ClO3

-+ H2O, o=1.19V,pH=0

ClO4-+ H2O + 2e = ClO3

-+ 2OH

-, o=0.36V,pH=14

Trong mi trng acid, v c H+tham gia vo qu trnh:

V vy tng H+

(gim pH) s dn n tng , hay tng tnh Oxyha, ngc li.

Tng t trong mi trng base, khi tng OH -(tng pH) s gimhay tng tnh kh, ngc li.

)(][

]][[lg

059.019.1

3

2

4V

ClO

HClO

n

)(]][[

][lg

059.036.0

2

3

4V

OHClO

ClO

n

GIN LATIMER NH HNG CA pH VI CC HP CHT CA Mn GIN LATIMER


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07/09/20

4. GIN FROST

Gin Frost biu din s tng quan gia G (thng qua i

lng nE tnh bng V) v cc trng thi oxy ha ca nguyn

t.

thit lp gin , trc ht ta tnh gi tr nE cho tt c cc

cp X(N)/X(0) (N l s oxy ho ca nguyn t X). V gin

phi lin tc (linear) cho nn cn tnh c trng hp X(N)

khng bn. V d sau cho Mn, l mt trong nhng trng hp

phc tp.

GIN LATIMER GIN LATIMER

S dng gin Frost

1. Nhndngtc nhn khv tc nhn oxy ha:

o Hp cht nm pha trn l cht oxy ha i vi cht nm bn

tri ca chng. Ngc li, hp cht bn trn s l cht kh

i vi cht bn phi ca chng.

o Hoc da vo h s gc a ca cc on thng ni cc trng

thi oxy ha: Nu a>0 th cu t cao hn l cht oxy ha, nua


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07/09/20

3. Nhn bit sn phm ca phn ng O-K:

Hp cht y gin c G nh, nn t c kh nng phn ng. Nn

hp cht y thng l sn phm (ng hc) cui ca qu trnh O -

K. Trong VD l Mn2+trong mi trng acid v Mn2O3trong mi

trng base.

4. Nhn bit qu trnh d ly:

Hp cht nm pha trn ng ni ca 2 cu t ln cn n s d b d

ly thnh 2 hp cht ln cn . VD trong mi trng base:

2MnO43-+2H2O MnO42-+ MnO2+ 4OH-

5. Nhn bit qu trnh a hp:

Hp cht nm pha di ng ni ca 2 cu t ln cn n s d to

thnh t 2 hp cht ln cn . VD trong mi trng acid: MnO2v

Mn s phn ng to Mn2+.

GIN FROST

Ncc ththam giaphnngoxy hakhvivai

tr l chtkhcaO (-2) v vai tr chtoxy ha ca

H(+1).

Trong iukinc th,chtno c thkh lnhn

thkhcacpO2/H2O th c khnngoxy ha c

nc. Tri li,chtno c thkhnhhnthkhcp

H2O/H2th c khnngkhcnc.

S N NH CA CC CHT OXY HA V CHT

KH TRONG MI TRNG NC

iu kin n nh ca cht kh trong dung dch nc

Cht kh

iu kin khng tiu chun, th kh ca cp 2H+/H2 25oC c tnhtheo cng thc Nernst:

Tnh oxy ha ca nc trong cc iu kin pH khc nhau c th hinqua th kh :

Mi trng acid : (pH = 0) 2H++ 2e H2 = 0,000V

Mi trng base: (pH =14)2H2O + 2e H2 + 2OH

- = -0,83V

Mi trng trung tnh: (pH = 7)

2H2O + 2e H2 + 2OH- = - 0,41V

Nh vy cht no c th kh ln hn cc gi tr th kh cho trn iukin pH xt l cht bn trong dung dch nc.

pH059,0plg0259,0]H[

plg

2

059,02

2

H2

2

H0

S N NH CA CC CHT OXY HA V CHTKH TRONG MI TRNG NC Chtoxy ha

iu kin khng tiu chun th kh ca cp O2/H2O 25oC ctnh theo cng thc Nernst:

Tnh kh ca nc cc mi trng khc nhau th hin qua thkh:

Mi trngacid: (pH = 0,O2(k)+4H++ 4e2H2O, =1,23V

Mi trngbase: (pH = 14),O2(k)+2H2O+4e4OH-, = 0,401V

M.trng trung tnh (pH = 7):

O2(k) + 4H+ + 4e 2H2O = 0,815V

Nh vy cht no c th kh nh hn th kh cho trn iu kinpH xt l cht bn trong dung dch nc. (xem v d v phn ngvi nc)

2

2

O

4

0

]OH[

p]H[lg

4

059,02

S N NH CA CC CHT OXY HA V CHTKH TRONG MI TRNG NC


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07/09/20

So snh khnngphnng khi sdng ct (SiO2) vkhi khng s dng ct SiO2 trong phn ng honnguyn qungphosphorite

Cc sliunhittothnh chunv entropy chuncacc cht250C

Ca3(PO4)2(n t)

C(graphite)

SiO2(thchanh)

CaSiO3(tam t)

CO(kh)

P4(trng)

CaO(lpphng)

0t,298

(kJ/mol)-4105 0 -912 -1635 -110 0 -635

S0298(J/mol.K)

+241 +6 +41 +82 +198 +164 +43


KH TRONG MI TRNG NC Phnngkhng sdngct:

2Ca3(PO4)2 + 10C = 6CaO + 10CO + P4

Phnngc sdngct:

2Ca3(PO4)2 + 10C + 6SiO2 = 6CaSiO3 + 10CO + P4

Nhn xt: Khi s dng ct th phn ng xy ra thun li hn rt nhiu v ct ngvai tr acid lm tng kh nng oxy ha ca phosphorite (back)

kJ22,2S1773HG

K/J1860)6102412()16410198436(S

kJ3300)241050()0101106635(H

0

298,pu

0

298,pu

0

1773,pu

0

298,pu

0

298,pu

Hpu,2980

= (

16356 11010+ 0) (0 41052 9126) = 2772kJ

Spu,2980

= (682+19810+164) (2241+106+ 641)=1848J/K

Gpu,17730

= Hpu,2980

1773 Spu,2980

= 504,5kJ


KH TRONG MI TRNG NC

V d: Xt xem cht no trong cc cht sau v phng

Din nhit ng ha hc c th bn trong dung dch nc

(khng c mt khng kh):

CoCl3, CrSO4, FeCl3, KMnO4, Na2SO3.

Bit rng chng u tan nhiu trong nc.

Th kh tiu chun trong mi trng acid:

Co3+/Co2+ Cr3+/Cr2+ Fe3+/Fe2+ MnO4-/Mn2+ SO4

2-/H2SO3

(V) 1,84 -0,41 0,771 1,51 0,17


Gii:

So snh vi cc gi tr th kh tiu chun ca nc chng ta c trong mitrng acid:

Cht kh: Na2SO3bn v c = 1,17V > 0,000V;

CrSO4khng bn v c = -0,41V < 0,000V

2Cr2++ 2H+ = 2Cr3++ H2

Cht oxy ha: FeCl3bn v c = 0,771 V< 1,23V.

khng bn v c = 1,84V > 1,23V 4 Co3++ 2H2O = 4Co

2++ O2+ 4H+

KMnO4khng bn v c = 1,51V > 1,23V

Tuy nhin do vn ng hc phn ng oxy hakh gia kali permanganatv nc thc t khng din ra m xy ra s phn hy chm ca ion

permanganat trong nc:

4MnO4-+ 4H+= 3O2+ 4MnO2 + H2O



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07/09/20

Th kh tiu chun trong mi trng base:

MnO4-/MnO2(=0,6V), SO42-/SO32-(=-0,93V)

Trong mi trng base:

Chtkh:

Na2SO3khngbnv c = -0,93 < -0,83V

Tuy nhin phn ng kh nc gii phng hydro ca ion sulfurous (SO32-)

khng xy ra do vn ng hc.

Chtoxy ha:

KMnO4khngbnv c = 0,6 > 0,401V

Tuy nhin do vn ng hc phn ng oxy hakh gia kali permanganat v

nc thc t khng din ra.

Cc cht cn li to hydroxide t tan nn khng bn n y (chng khng cn l

mui na).


KH TRONG MI TRNG NC

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