redox reactions half-reactions: reduction 2fe 3+ + 2e - 2fe 2+ oxidation sn 2+ sn 4+ + 2e - 2fe 3+...
TRANSCRIPT
Redox reactions
half-reactions:
Reduction
2Fe3+ + 2e- 2Fe2+
oxidation
Sn2+ Sn4+ + 2e-
2Fe3+ + Sn2+ 2Fe2+ + Sn4+
9203091 http:\asadipour.kmu.ac.ir 34 slides
Redox reactionsoccurring in
1) solution
2) electrochemical cell.
2Fe3+ + Sn2+ 2Fe2+ + Sn4+
9203092 http:\asadipour.kmu.ac.ir 34 slides
Electrochemical Reactions
1)chemical electric:
primary cell (Galvanic cell)
2)electric chemical:
electrolytic cell
9203093 http:\asadipour.kmu.ac.ir 34 slides
Standard Reduction PotentialsReduction Half-Reaction E(V)
F2(g) + 2e- 2F-(aq) 2.87
Au3+(aq) + 3e- Au(s) 1.50
Cl2(g) + 2 e- 2Cl-(aq) 1.36
Cr2O72-(aq) + 14H+(aq) + 6e- 2Cr3+(aq) + 7H2O 1.33
O2(g) + 4H+ + 4e- 2H2O(l) 1.23
Ag+(aq) + e- Ag(s) 0.80
Fe3+(aq) + e- Fe2+(aq) 0.77
Cu2+(aq) + 2e- Cu(s) 0.34
Sn4+(aq) + 2e- Sn2+(aq) 0.15
2H+(aq) + 2e- H2(g) 0.00
Sn2+(aq) + 2e- Sn(s) -0.14
Ni2+(aq) + 2e- Ni(s) -0.23
Fe2+(aq) + 2e- Fe(s) -0.44
Zn2+(aq) + 2e- Zn(s) -0.76
Al3+(aq) + 3e- Al(s) -1.66
Mg2+(aq) + 2e- Mg(s) -2.37
Li+(aq) + e- Li(s) -3.04
Ox.
age
nt s
tren
gth
incr
ease
sR
ed. agent strength increases
9203094 http:\asadipour.kmu.ac.ir 34 slides
Balancing of redox reactions.Under Acidic conditions
1. Identify oxidized and reduced species Write the half reaction for each.
2. Balance the half rxn separately except H & O’s.
Balance: Oxygen by H2OBalance: Hydrogen by H+
Balance: Charge by e -
3. Multiply each half reaction by a coefficient. There should be the same # of e- in both half-rxn.
4. Add the half-rxn together, the e - should cancel.9203095 http:\asadipour.kmu.ac.ir 34
slides
Balancing of redox reactions.Under Basic conditions
1. Identify oxidized and reduced species Write the half reaction for each.
2. Balance the half rxn separately except H & O’s.
Balance: Oxygen by H2OBalance: Hydrogen by OH-
Balance: Charge by e -
3. Multiply each half reaction by a coefficient. There should be the same # of e- in both half-rxn.
4. Add the half-rxn together, the e - should cancel.9203096 http:\asadipour.kmu.ac.ir 34
slides
Balancing of redox reactionsH2O2 (aq) + Cr2O7
-2(aq ) Cr 3+
(aq) + O2 (g) Redox reaction
======================================
1)write 2 half reactions
Half Rxn (red): Cr2O7
-2 (aq) Cr3+
Half Rxn (oxid):
H2O2 (aq) O2
2)Atom balanceCr2O7
-2 (aq) 2Cr3+
H2O2 (aq) O29203097 http:\asadipour.kmu.ac.ir 34
slides
Balancing of redox reactions
3)Oxygen balanceHalf Rxn (red): Cr2O7
-2 (aq) 2Cr3+ + 7 H2O
Half Rxn (oxi): H2O2 (aq) O2
4)Hydrogen balanceHalf Rxn (red): 14H+ + Cr2O7
-2 (aq) 2Cr3+ + 7 H2O
Half Rxn (oxi): H2O2 (aq) O2 + 2H+
5)Electron balance6e- + 14H+ + Cr2O7
-2 (aq) 2Cr3+ + 7 H2O
H2O2 (aq) O2 + 2H+ + 2e-
9203098 http:\asadipour.kmu.ac.ir 34 slides
Balancing of redox reactions
6) Equalize of produced and consumed electrons
6e- + 14H+ + Cr2O7-2
(aq) 2Cr3+ + 7 H2O
( H2O2 (aq) O2 + 2H+ + 2e- ) x 3
7)Multiply each half reaction8 H+ + 3H2O2 + Cr2O7
2- 2Cr+3 + 3O2 + 7H2O
9203099 http:\asadipour.kmu.ac.ir 34 slides
Balance the redox reactions
I2 +S2O32- ⇋ I- +S4O62-
I2 +S2O32- ⇋ I- +SO42-
92030910 http:\asadipour.kmu.ac.ir 34 slides
H+
OH-
Redox titration
2Ag+ + Cu(S) 2Ag(s) + Cu2+ Redox reaction---------------------------------------------------------------------
Cu│Cu2+ (xM) ││ Ag+(yM) │ Ag
Cu2+ + 2e- Cu(S) Eo=0.337Ag+ + e- Ag(s) Eo =0.799
•
][
][k•
2
2
eq
Ag
Cu
92030911 http:\asadipour.kmu.ac.ir 34 slides
Redox titration
ECell=0 → EAg =ECu درتعادل
92030912 http:\asadipour.kmu.ac.ir 34 slides
2Ago
Ag ][Ag
1Log
2
0.059-EE•
][Cu
1Log
2
0.059-EE•
2Cuo
Cu2
2Ag+ + Cu(S) 2Ag(s) + Cu2+ Redox Eo =0.462
ECell=Ecathod-Eanod=EAg-ECu
Keq
][Cu
1Log
2
0.059-CuE
][Ag
1Log
2
0.059-Ag E
22
2oo
CuE- AgE• 2oo
][Cu
1Log
2
0.059 -
][Ag
1Log
2
0.05922
]Log[Cu2
0.059
][Ag
1Log
2
0.059 22
2] [Ag
][Cu2 Log
2
0.059
E E -E• redoxo2Cu
o
Ag
o
059.0
2log
] [Ag
][Cu2 Log 0
2
redoxEK qe
104.1K•
15.60.059
0.337)-2(0.799logK•
15eq
eq
92030913http:\asadipour.kmu.ac.ir 34
slides
EAg = ECu
Keq
•MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
•MnO4-+5e-+8H+→ Mn2++ 4H20 E0=1.51 n=5
•5Fe2 +→ 5Fe3+ +5e E0= -0.771 n=1
92030914 http:\asadipour.kmu.ac.ir 34 slides
62.50.059
0.771)-1(1.515LogK• eq
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M (1M H2SO4)•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Fe3+ + e Fe2+ E0=0.7715ml Before Eq
92030915 http:\asadipour.kmu.ac.ir 34 slides
][Fe
][FeLog0.059-0.771E•
3
2
MNVV
VNVNFe 357.0357.0
105
5.255.0100
21
2211][ 2
MNVV
VNFe 119.0119.0
105
5.25
21
22][ 3
V743.00.119
0.357Log0.059-0.771E•
Attention 1!!!!!!
•100 ml Fe2+ 0.5 M WITH Mno4- 0.5 M
•MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
•Fe2+ Fe3+ + e E0=-0.771
5ml Before Eq
92030916 http:\asadipour.kmu.ac.ir 34 slides
][Fe
][FeLog0.059-0.771E•
2
3
MNVV
VNVNFe 357.0357.0
105
5.255.0100
21
2211][ 2
MNVV
VNFe 119.0119.0
105
5.25
21
22][ 3
!!!!!!!!!!743.00.357
0.119Log0.059-0.771E• V
Attention 2!!!!!!
•100 ml Fe2+ 0.5 M WITH Mno4- 0.5 M
•MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
•5Fe2+ 5Fe3+ + 5e E0=-0.771
5ml Before Eq
92030917 http:\asadipour.kmu.ac.ir 34 slides
52
53
][Fe
][FeLog
5
0.059-0.771E•
MNVV
VNVNFe 357.0357.0
105
5.255.0100
21
2211][ 2
MNVV
VNFe 119.0119.0
105
5.25
21
22][ 3
!!!!!!!!743.0(0.357)
(0.119)Log
5
0.059-0.771E•
5
5
V
Titration curve
•100 ml Fe2+ 0.5 M WITH Mno4- 0.5 M
•MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
•Fe3+ + e Fe2+ E0=0.771
10 ml Before Eq
92030918 http:\asadipour.kmu.ac.ir 34 slides
][Fe
][FeLog0.059-0.771E•
3
2
MNVV
VNVNFe 045.0227.0
110
5.2105.0100
21
2211][ 2
MNVV
VNFe 045.0227.0
105
5.210
21
22][ 3
V771.00.045
0.045Log0.059-0.771E•
Titration curve
•100 ml Fe2+ 0.5 M WITH Mno4- 0.5 M
•MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
•Fe3+ + e Fe2+ E0=0.771
15 ml Before Eq
92030919 http:\asadipour.kmu.ac.ir 34 slides
][Fe
][FeLog0.059-0.771E•
3
2
MNVV
VNVNFe 109.0109.0
115
5.2155.0100
21
2211][ 2
MNVV
VNFe 326.0326.0
115
5.215
21
22][ 3
V799.00.326
0.109Log0.059-0.771E•
Titration curve
•100 ml Fe2+ 0.5 M WITH Mno4- 0.5 M
•MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
•Fe3+ + e Fe2+ E0=0.771
19 ml Before Eq
92030920 http:\asadipour.kmu.ac.ir 34 slides
][Fe
][FeLog0.059-0.771E•
3
2
MNVV
VNVNFe 021.0021.0
119
5.2195.0100
21
2211][ 2
MNVV
VNFe 399.0328.0
119
5.219
21
22][ 3
V846.00.399
0.021Log0.059-0.771E•
Titration curve
•100 ml Fe2+ 0.5 M WITH Mno4- 0.5 M
•MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
•Fe3+ + e Fe2+ E0=0.771
19.5 ml Before Eq
92030921 http:\asadipour.kmu.ac.ir 34 slides
][Fe
][FeLog0.059-0.771E•
3
2
MNVV
VNVNFe 010.0010.0
5.119
5.25.195.0100
21
2211][ 2
MNVV
VNFe 408.0408.0
5.119
5.25.19
21
22][ 3
V866.00.408
0.010Log0.059-0.771E•
Titration curve•1e+Fe3+ Fe2+ 5+MnO4
-+8H+ Mn2+
20 ml At Eq
92030922 http:\asadipour.kmu.ac.ir 34 slides
]][H[MnO
][Mn Log
5
0.059-EE•
8-4
2
MnOeq 4
][Fe
][FeLog0.059-E•
3
2
Feeq
E
]][H[MnO
][Mn Log0.059-E55E•
8-4
2
MnOeq 4
]][H][MnO[Fe
]][Mn[Fe Log0.059-E56E•
8-4
3
22
MnOeq 4
FeE
×5
Titration curve
92030923 http:\asadipour.kmu.ac.ir 34 slides
]][H][MnO[Fe
]][Mn[Fe Log0.059-E56E•
8-4
3
22
MnOeq 4
FeE
][H
1 Log0.059-E56E•
8MnOeq 4 FeE
][H
1 Log
6
0.059-
6
E5E
8
MnO
eq4
FeE
MnO4-+5Fe2++8H+ Mn2++5Fe3++4H20
/6
5X
X
Y
5Y
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Fe3+ Fe2+
•Mno4-+8H+ Mn2+
xHLog
nm
x
][
1
)(
059.0
n)(m
redmE onEE•
00
20 ml At Eq
92030924 http:\asadipour.kmu.ac.ir 34 slides
V387.115
771.0151.15
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Mno4-+8H+ Mn2+
]][H[MnO
][Mn Log
5
0.059-1.51E•
8-4
2
20.5 ml After Eq
92030925 http:\asadipour.kmu.ac.ir 34 slides
1.491V 10.002
0.083 Log
5
0.059-1.51E•
8
MNVV
VNMn 083.0415.0
5.120
5.0100
21
11][ 2
MNVV
VNVNMnO 002.0010.0
5.120
5.01005.25.20
21
1122][ 4
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Mno4-+8H+ Mn2+
]][H[MnO
][Mn Log
5
0.059-1.51E•
8-4
2
21 ml After Eq
92030926 http:\asadipour.kmu.ac.ir 34 slides
1.494V 10.004
0.083 Log
5
0.059-1.51E•
8
MNVV
VNMn 083.0413.0
121
5.0100
21
11][ 2
MNVV
VNVNMnO 004.0021.0
121
5.01005.221
21
1122][ 4
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Mno4-+8H+ Mn2+
]][H[MnO
][Mn Log
5
0.059-1.51E•
8-4
2
22 ml After Eq
92030927 http:\asadipour.kmu.ac.ir 34 slides
1.498V 10.008
0.082 Log
5
0.059-1.51E•
8
MNVV
VNMn 082.0410.0
122
5.0100
21
11][ 2
MNVV
VNVNMnO 008.0041.0
122
5.01005.222
21
1122][ 4
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Mno4-+8H+ Mn2+
]][H[MnO
][Mn Log
5
0.059-1.51E•
8-4
2
23 ml After Eq
92030928 http:\asadipour.kmu.ac.ir 34 slides
1.500V 10.012
0.081 Log
5
0.059-1.51E•
8
MNVV
VNMn 081.0407.0
123
5.0100
21
11][ 2
MNVV
VNVNMnO 012.0061.0
123
5.01005.223
21
1122][ 4
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Mno4-+8H+ Mn2+
]][H[MnO
][Mn Log
5
0.059-1.51E•
8-4
2
25 ml After Eq
92030929 http:\asadipour.kmu.ac.ir 34 slides
1.503V 10.02
0.08 Log
5
0.059-1.51E•
8
MNVV
VNMn 08.04.0
125
5.0100
21
11][ 2
MNVV
VNVNMnO 02.01.0
125
5.01005.225
21
1122][ 4
Titration curve•100 ml Fe2+ 0.5 M WITH Mno4
- 0.5 M•MnO4
-+5Fe2++8H+ Mn2++5Fe3++4H20
•Mno4-+8H+ Mn2+
]][H[MnO
][Mn Log
5
0.059-1.51E•
8-4
2
30 ml After Eq
92030930 http:\asadipour.kmu.ac.ir 34 slides
1.504V 10.023
0.077 Log
5
0.059-1.51E•
8
MNVV
VNMn 077.0385.0
130
5.0100
21
11][ 2
MNVV
VNVNMnO 023.0115.0
130
5.01005.230
21
1122][ 4
Titration curve
92030931 http:\asadipour.kmu.ac.ir 34 slides
ml of MnO4K E(v) ΔE/ΔV Δ2E/ΔV2
5 0.74310 0.771 0.005615 0.799 0.0056 019 0.846 0.01175 0.001537
19.5 0.866 0.04 0.056520 1.387 1.042 2.004
20.5 1.491 0.208 -1.66821 1.494 0.006 -0.40422 1.498 0.004 -0.00223 1.5 0.002 -0.00225 1.503 0.0015 -0.0002530 1.504 0.0002 -0.00026
Titration curve data
92030932 http:\asadipour.kmu.ac.ir 34 slides
0 5 10 15 20 25 30 350
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
ml of titrant
E
Height is related to Keq
Not related to concentration
Titration curve
92030933 http:\asadipour.kmu.ac.ir 34 slides
0 5 10 15 20 25 30 350
0.2
0.4
0.6
0.8
1
1.2
ml of titrant
ΔE
/ΔV
Titration curve
92030934 http:\asadipour.kmu.ac.ir 34 slides
0 5 10 15 20 25 30 35
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
ml of titrant
Δ2E
/ΔV
2