chuong11- dien hoa
TRANSCRIPT
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CHNG 11
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Phan ng oxy hoa kh (O K)
Phan ng trong o co s trao
oi electron gia cac nguyen tcua nhng nguyen to tham gia phan
ng lam thay oi so oxy hoa cac
nguyen to.
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Qua trnh cho electron goi la quatrnh oxy hoa, chat cho electron goila chat kh(chat b oxy hoa).
V du:
Zn 2e' Zn+2 Qua trnh nhan electron goi la
qua trnh kh, chat nhan electron
goi la chat oxy hoa. V du:
Cu+2 + 2e ' Cu
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Phn ng tng quat:
Qt oxh: hI ' OxI + neQt kh: OxII + ne ' hIIPt oxh kh: hI + OxII ' OxI +
KhII
Cap oxy hoa kh: OxI/KhI , OxII/KhII
Vdu:
Qt oxh: Zn ' Zn2+ + 2e
Qt kh: Cu2+ + 2e ' Cu
Pt oxh kh: Zn + Cu2+ Zn2+ + Cu
Pt phan t: Zn + CuSO4 ZnSO4 + Cu
Cap oxy hoa kh: Zn2+/Zn; Cu2+/Cu
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Nguyen tac 1: Tong so electron cho cua chat kh
phai bang tong so electron chat oxyhoa nhan vao.
Cac bc tien hanh can bang. Bc 1: Xac nh s thay oi so oxy
hoa cua cac chat. Bc 2: Lap phng trnh electron ion,
vi he so sao cho ung qui tac tren.
Bc 3: Thiet lap phng trnh ion cua
phan ng.
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Vdu:Al + CuSO4 p Al2(SO4)3 + Cu
Al - 3e p Al+3
Cu+2
+ 2e p Cu2Al + 3Cu+2 = 2Al+3 + 3Cu
2Al + 3CuSO4 p 2Al2(SO4)3 + 3Cu
X2
X3
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Nguyen tac 2:
oi vi phan ng O K xay ra trongmoi trng acid neu dang Ox cua chatOx co cha nhieu nguyen t Oxy hn
dang kh cua no th phai them H+
vaove tr ai (dang Ox) va them nc vaove phai (dang kh).
Neu dang kh cua chat Kh cha t
nguyen t Oxy hn dang Ox cua no ththem nc vao ve tr ai (dang Kh) va H+
vao ve phai (dang Ox).
Thieu O ben nao, them H2O ben o,ben kia them H+
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Vdu:
OHSOKKNOMnSOSOHKNOKMnO 242344224 p
p
p
32
2
4
2
5
NOeNO
MneMnO
OHMnHeMnO 22
4 485 p
p HNOOHeNO 22
322
OHSOKKNOMnSOSOHKNOKMnO
OHNOMnHNOMnO
242344224
2324
352352
352652
!
!
X2
X5
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Nguyen tac 3:
Phan ng O K xay ra trong moitrng base, neu dang Ox cua chatOx cha nhieu Oxy hn dang kh th
phai them nc vao ve tr ai, OH-vao ve phai.
Neu dang Kh cua chat Kh cha t Oxyhn dang Ox cua no th phai themOH- vao ve trai, nc vao ve phai.
Thieu O ben nao them OH- ben o,ben kia la H
2
O.
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Vdu:
X1
X2
OHKClCrOKKOHCrClKClO24233
p
! OHClOHeClO 636 23
OHCrOOHeCr 22
4
3 483 !
OHCrOClOHCrClO2
2
4
3
3522 !
OHCrOKKClKOHCrClKClO 24233 527102 !
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Nguyen tac 4:
Phan ng O-K trong moi trngtrung tnh. Neu dang Ox cua chat Oxcha nhieu nguyen t Oxy hn
dang Kh cua no th phai themnc vao ve trai, OH- vao ve phai.
Neu dang Kh cua chat Kh cha tnguyen t Oxy hn dang Ox cua no
th phai them nc vao ve tr ai, H+vao ve phai.
Them nc ve trai het, ve phai:- +
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Vdu:
X2
X3
KOHKNOMnOOHKNOKMnO p 32224
! OHMnOOHeMnO 423 224
! HNOOHeNO 22
322
! HOHNOMnOOHNOMnO 6832732
32224
! OHNOMnOOHNOMnO 23232
32224
KOHKNOMnOOHKNOKMnO 23232 32224 !
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Phan ng O K va dongien
ieu kien bnh thng, phan ng O K xay racung mot ni th hoa nang se bien thanh nhietnang.
ieu kien ac biet phan ng O K xay ragian tiep hai ni khac nhau th hoa nang sebien thanh ien nang (qua day dan).e-
Chat kh
e-
e-
Cha
t oxhAnode Cathode
Mang ngan
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Nguyen to galvanic(1780): La thiet b chuyen hoa
nang sang ien nang.Cau tao gom hai thanh kimloai, nhung trong dung dchmuoi cua no, noi vi
nhau qua si day dan kimloai.
Hai thanh kim loai nay mot
thanh co tnh kh manhhn e cho e mot thanh
Luigi Galvani (Italia)
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Cathode (+), xay raqua trnh kh
Anode (-) , xay raqua trnh oxy hoa
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ien cc kem:Zn 2e p Zn+2 goi la am cc (Cathode)
ien cc ong:Cu+2 + 2e p Cu goi la dng cc (Anode)
Tc la am cc xay ra qua trnh Oxy hoa,Zn la chat Kh. dng cc xay ra qua trnhkh, Cu la chat Ox.
Phng trnh cua galvanic:Zn+Cu+2 = Zn+2 + Cu
Ngi ta ky hieu nguyen to ganvanic:
Hay
Tong quat:
CuCuSOZnSOZn44
CuCuZnZn 22
IIIIII
MddMddMM
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The ien cc N (V), hay con goi lathe Oxy hoa Kh, hay la ban thephan ng, la mot ai lng khong
the o tr c tiep, ma phai so sanhvi mot ien cc chuan. Ngi ta chon Hydro lam ien cc
chuan:
2H+(dd) + 2e p H2 (k), ien cc laplatinum.Quy c: N0H2 = 0 (V). (The ien cc
tuyet oi cua no c chng 4.4 4.6
V)
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Phng trnh Nernst:
Kh ne p Ox, N
Vi a la hoat o. Hoat o cua cac kimloai tinh khiet (va ca long tinh khiet) coinh bang 1.
Vi dung dch that (s dung C) nhieto 298K, ta co (R=8.31, T=298,F=96500):
Kh
Ox
a
a
nF
RTln
0!NN
][
][lg
059.000
Kh
Ox
n! NN
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N phu thuoc vao ban chat chat thamgia qua trnh ien cc (N0, n) nhiet oT, nong o chat tham gia qua trnhien cc C.
Ta co:UG = -nFN, hayUG0 = -nFN0
Sau ay la bang the ien cc tieuchuan cua mot so ban phan ng(The Ox-Kh).
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Banphan ng1bar,298K, Ci = 1M
N0 (V)
Li+(aq) + e Li(s) 3.05
K+(aq) + e K(s) 2.93
Ba2+(aq) + 2e Ba(s) 2.91
Ca2+(aq) + 2e Ca(s) 2.76
Na+(aq) + e Na(s) 2.71
Mg2+(aq) + 2e Mg(s) 2.38
Be2+(aq) + 2e Be(s) 1.85
Al3+(aq) + 3e Al(s) 1.68
Ti3+(aq) + 3e Ti(s) 1.21
Mn2+(aq) + 2e Mn(s) 1.18
Sn(s) + 4H+ + 4e SnH4(g) 1.07
2 H2O(l)+2eH
2(g)+2OH(aq) 0.83
Zn2+(aq) + 2e Zn(s) 0.76
Cr3+(aq) + 3e Cr(s) 0.74
Fe2
+(aq) + 2e Fe(s) 0.44
Cr3+(aq) + e Cr2+(aq) 0.42
Sn2+(aq) + 2e Sn(s) 0.13
2H+(aq) + 2e H2(g) 0.00
Sn4+(aq) + 2e Sn2+(aq) +0.15
Cu2+(aq) + e Cu+(aq) +0.16
SO42(aq) + 4H+ + 2e
2H2O(l) + SO
2(aq)
+0.17
Cu2+(aq) + 2e Cu(s) +0.34
O2(g)+2H
2O(l)+4e 4OH(aq) +0.40
SO2(aq)+4H++4eS(s)+ 2H
2O +0.50
Cu+(aq) + e Cu(s) +0.52
I2(s) + 2e 2I(aq) +0.54
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MnO4(aq) + 2H
2O(l) + 3e
MnO2(s) + 4 OH(aq)
+0.59
S2O32
+ 6H+ + 4e 2S(s) +3H
2O
+0.60
O2(g) + 2H+ + 2e H
2O
2(aq) +0.70
Fe3+(aq) + e Fe2+(aq) +0.77
Hg22+(aq) + 2e 2Hg(l) +0.80
Ag+(aq) + e Ag(s) +0.80
NO3(aq) + 2H+(aq) +e
NO2(g) + H
2O(l)
+0.80
Hg2+(aq) + 2e Hg(l) +0.85
MnO
4
(aq) + H+
+ e
HMnO4
(aq)+0.90
2Hg2+(aq) + 2e Hg22+(aq) +0.91
MnO2(s) + 4H+ + e Mn3+(aq)
+ 2H2O
+0.95
Br2(aq) + 2e 2Br(aq) +1.09
2IO3(aq) + 12H+ + 10e I
2(s)
+ 6H2O
+1.20
ClO4(aq) + 2H+ + 2e
ClO3(aq) + H
2O
+1.20
O2(g) + 4H+ + 4e 2H
2O +1.23
MnO2(s) + 4H+ + 2e
Mn2+(aq) + 2H2O
+1.23
Cl2(g) + 2e 2Cl(aq) +1.36
Cr2O7
2(aq) + 14H+ + 6e
2Cr3+(aq) + 7H2O
+1.36
MnO4(aq) + 8H+ + 5e
Mn2+(aq) + 4H2O
+1.51
2HClO(aq) + 2H+ + 2e Cl2(g)+ 2H
2O
+1.63
MnO4(aq) + 4H+ + 3e
MnO2(s) + 2H
2O
+1.70
H2O
2(aq) + 2H+ + 2e 2H
2O +1.76
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The hieu cc ai xuat hien gia haicc ca nguyen to ganvanic goi la scien ong cua nguyen to ganvanic,khi ma nguyen to galvanic hoat ong T
N.
Khieu:
Sc ien ong tieu chuan cuanguyen to galvanic. E0 o p = 1 atm, CM
(hay a) = 1, 298K.
NN!E
000
E NN!
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aKh1 + bOXH2' cOXH1 + dKh2
-(G = A = nFE
b
2
a
1
d
2
c
10
OXHKh
KhOXHlnRTGG (!(
b
2
a
1
d
2
c
1
OXHKh
KhOXH
lnRTKlnRTnFE !
b
2
a
1
d
2
c
1
OXHKh
KhOXHln
nF
RTKln
nF
RTE !
KlnnF
RTE0 !
(G0
= -nFE0
ba
dc
OXHKh
KhOXH
nF
RTEE
21
210ln!
cd
sp
nF
RT
EEln
0!
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Vduviphan ng trongnguyen to
galvanic:Zn + Cu+2 = Zn+2 + Cu
ViN+ lacuacap Cu+2/Cu vaN- la
cuacap Zn+2
/Zn, taco
2
2
ln
2
0
//
!
Cu
Zn
ZnCuZnCu
C
C
F
RTEE
V...EZn/Cu
1176303370000
!!!
NN
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3324FeCeFeCeXet phan ng:
34CeeCe
23FeeFe N
o
=1.700V
No=0.767V
c tao thanh bi 2 ban phan ng sau
V No cua cerium ln hn nen no la chat Oxy hoa.Ta co
(0.767)-1.700-E ooo !!
NN
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Trong nguyen to galvanic co:
]][Ce[Fe
]][Ce[Feln
nF
RT---E
42
3300
-
!! NNNN
Tai can bang, E = 0 va:
1610K}
C25,Klog05916.]][Ce[Fe
]][Ce[Feln
F
RT- o
42
33oo v!!
NN
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Xet caccap O-K: Ox1/Kh1 , Ox2/Kh2
Kh1' Ox1 + ne ,N1
Kh2'
Ox2 + ne ,N2Khi troncaccapnay,se co phanng:
Kh1 + Ox2 ' Ox1 + Kh2
Phan ng xay ra theo chieu thuan khi:
121212
0 NNNN "!!( nFnFEG/
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Quy tac xet chieu phan ng:
Phan ng O K xay ra theo chieudang Ox cua cap O K co N ln hnse Ox dang Kh cua cap O K co N
nho hn.
Thc te co the dung N0 e xet.Nhng khi N0+ - N0- be qua thphai tnh toan tren N.