redox reactions

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+


Electrochemical Reactions

1)chemical electric:

primary cell (Galvanic cell)

2)electric chemical:

electrolytic cell


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


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-


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


Balance the redox reactions

I2 +S2O32- ⇋ I- +S4O62-

I2 +S2O32- ⇋ I- +SO42-


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


Redox titration

ECell=0 → EAg =ECu درتعادل


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


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


][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


][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


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


][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


][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


][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


][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


]][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


]][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


- 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


V387.115

771.0151.15


- 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


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


- 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


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


- 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


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


- 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


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


- 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


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


- 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


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


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


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


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


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

redox reactions

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