ib chemistry on standard reduction potential, standard hydrogen electrode and electrochemical series

Potential Diff bet Zn/Zn2+

Electrode potential Zn/Zn2+ = -ve

-

Electrode Potential

Redox Equilibrium

Zn2+

Zn → Zn 2+ + 2e (Oxidation)

Zn 2+ + 2e → Zn

(Reduction) Zn 2+ + 2e ↔ Zn

(At equilibrium)

Metal Zn placed in its sol Zn2+ ion

Equilibrium bet Zn/Zn2+

Zn metal reactive lose e form Zn2+

Equilibrium shift to right ←

Potential Diff form bet Zn/Zn2+

Potential Diff Electrode potential = -ve

Zn2+

Zn2+

Zn

Zn2+

Zn

Zn2+

Zn2+ Zn2+

Zn 2+ + 2e ↔ Zn Equi shift to ←

-

- -

Zn

- - -

-

+

+

+

+ + +

+ +

+

Voltage of Zn/Zn2+ can’t be measured. Abs electrode potential can’t measured. Only Diff in electrode potential can be measured.

Cannot measure

Abs Potential

Metal Cu placed in its sol Cu2+ ion

Equilibrium bet Cu/Cu2+

Cu2+ ion gain -2e form Cu

Equilibrium shift to left ←

Potential Diff form bet Cu/Cu2+

Potential Diff Electrode potential = +ve

Cu

Cu2+

Cu2+

Cu2+

Cu2+

Cu → Cu2+ + 2e (Oxidation)

Cu2+ + 2e → Cu

(Reduction) Cu2+ + 2e ↔ Cu

(At equilibrium)

Cu

-e

-e

-e

Cu2+

Cu2+

Cu2+

Cu2+ + 2e ↔ Cu Equi shift to →

Zn Half Cell

+

+ +

Cu

+ +

+

- - -

-

- - - - - - -

- -

Potential Diff bet Cu/Cu2+

Electrode potential Cu/Cu2+ = +ve

Cannot measure

Abs Potential

Voltage of Cu/Cu 2+ can’t be measured. Abs electrode potential can’t measured. Only Diff in electrode potential can be measured.

Click here chem database (std electrode potential)


Click here interactive ECS Click here pdf version ECS

Cu Half Cell

http://www.fptl.ru/biblioteka/spravo4niki/handbook-of-Chemistry-and-Physics.pdf

http://www.hbcpnetbase.com/


http://www.hbcpnetbase.com/

http://www2.hkedcity.net/sch_files/a/lsc/lsc-chem/public_html/nss/redox/ecs.html

http://downloads.gphysics.net/UACh/Medicina/TablasIones.pdf


http://downloads.gphysics.net/UACh/Medicina/TablasIones.pdf

Potential Diff Cu/Cu2+


Potential Diff Zn/Zn2+


Zn2+

Zn → Zn 2+ + 2e

(Oxidation)

Zn 2+ + 2e → Zn

(Reduction)

Zn 2+ + 2e ↔ Zn

(At equilibrium)

Zn2+

Zn2+

Zn

Zn2+

Zn

Zn2+

Zn2+ Zn2+

Zn 2+ + 2e ↔ Zn

Equi shift to ←

- -

-

Zn

- - -

- +

+ +

+

+ +

+ +

+

Can’t measure

Abs Potential

Cu

Cu2+

Cu2+

Cu2+

Cu2+

Cu → Cu2+ + 2e

(Oxidation)

Cu2+ + 2e → Cu

(Reduction)

Cu2+ + 2e ↔ Cu

(At equilibrium)

Cu

-e

-e -e

Cu2+

Cu2+

Cu2+

Cu2+ + 2e ↔ Cu

Equi shift to →

Zn Half Cell

+ +

+

Cu

+ + +

-

Cu Half Cell

Zn/Cu Voltaic Cell

External circuit – flow of electrons Complete circuit

- - -

- - -

- - - - - - - -

Connect 2 Half Cell with wire/ salt bridge

Zn half cell (-ve) Oxidation

Cu half cell (+ve) Reduction

Salt Bridge – flow of ions Complete the circuit

Cu2+ + 2e → Cu Zn → Zn 2+ + 2e

Zn + Cu2+ → Zn2+ + Cu

Anode Cathode

Maintain electrical neutrality

Salt bridge – saturated KNO3

Zn2+ increase ↑

NO3- flow in to balance excess Zn2+

Cu2+ decrease ↓, excess –ve ion ↑

K+ flow in to balance loss of Cu2+

Zn Cu

- - - -

Zn2+ Zn2+

Zn2+

Excess of Zn2+ ion

+ +

+ +

- - -

-

- - - - - -

- -

Excess of –ve ion

+ + +

+ + +

+

Without Salt Bridge

- + +

+

+

With Salt Bridge

(electron unable to flow due to ESF)

NO3-

NO3-

NO3-

NO3-

+

+

+ K+

K+

K+

-

- -

K+ flow in to balance

excess of – ion

NO3- flow in to balance

excess of + ion

2 Half Cell to make a Voltaic Cell

-e -e

-

-

-

-

+

+

+

+





Zn2+

Zn → Zn 2+ + 2e

(Oxidation)

Zn 2+ + 2e → Zn

(Reduction)

Zn 2+ + 2e ↔ Zn

(At equilibrium)

Zn2+

Zn2+

Zn

Zn2+

Zn

Zn2+

Zn2+ Zn2+

Zn 2+ + 2e ↔ Zn

Equi shift to ←

- -

-

Zn

- - -

- +

+ +

+

+ +

+ +

+

Can’t measure

Abs Potential

Cu

Cu2+

Cu2+

Cu2+

Cu2+

Cu → Cu2+ + 2e

(Oxidation)

Cu2+ + 2e → Cu

(Reduction)

Cu2+ + 2e ↔ Cu

(At equilibrium)

Cu

-e

-e -e

Cu2+

Cu2+

Cu2+

Cu2+ + 2e ↔ Cu

Equi shift to →

+ +

+

Cu

+ + +

-


- - -

- - -

- - - - - - - -




Voltmeter – High resistance (No current flow) Salt Bridge – flow of ions

Complete the circuit

Cu2+ + 2e → Cu Zn → Zn 2+ + 2e

1.10Volt Potential diff can be measured.

Voltmeter across – EMF

1.10 Volt

Zn + Cu2+ → Zn2+ + Cu

Anode Cathode

Zn(s) | Zn2+(aq) || Cu2+

(aq)| Cu (s)

Cell diagram

Anode Cathode

Half Cell Half Cell (Oxidation) (Reduction)

Phase boundary Salt Bridge Flow

electrons



Zn2+ increase ↑


Cu2+ decrease ↓

K+ flow in to balance loss of Cu2+

Zn/Cu Voltaic Cell 2 Half Cell to make a Voltaic Cell

Zn Half Cell Cu Half Cell

-e -e

-

-

-

-

+

+

+

+

Potential Diff Ag/Ag2+

Electrode potential Ag/Ag2+ = +ve



Zn2+

Zn → Zn 2+ + 2e

(Oxidation)

Zn 2+ + 2e → Zn

(Reduction)

Zn 2+ + 2e ↔ Zn

(At equilibrium)

Zn2+

Zn2+

Zn

Zn2+

Zn

Zn2+

Zn2+ Zn2+

Zn 2+ + 2e ↔ Zn

Equi shift to ←

- -

-

Zn

- - -

- +

+ +

+

+ +

+ +

+

Can’t measure

Abs Potential

Ag

Ag+

Ag+

Ag+

Ag+

Ag → Ag+ + e

(Oxidation)

Ag+ + e → Ag

(Reduction)

Ag+ + e ↔ Ag

(At equilibrium)

Ag

-e

-e -e

Ag+

Ag+

Ag+

Ag+ + e ↔ Ag

Equi shift to →

+ +

+

Ag

+ + +

-


- - -

- - -

- - - - - - - -



Ag half cell (+ve) Reduction



Ag+ + e → Ag Zn → Zn 2+ + 2e



1.56 Volt

Zn + 2Ag+ → Zn2+ + 2Ag

Anode Cathode

Zn(s) | Zn2+(aq) || Ag+

(aq)| Ag (s)

Cell diagram

Anode Cathode



electrons



Zn2+ increase ↑


Ag+ decrease ↓

K+ flow in to balance loss of Ag+

Zn/Ag Voltaic Cell 2 Half Cell to make a Voltaic Cell

Zn Half Cell Ag Half Cell

Ag

Ag+

-e -e

-

-

-

-

+

+

+

+

Potential Diff Ag/Ag2+

Electrode potential Ag/Ag2+ = +ve


Electrode potential Cu/Cu2+ = -ve

Cu2+

Cu → Cu 2+ + 2e

(Oxidation)

Cu 2+ + 2e → Cu

(Reduction)

Cu 2+ + 2e ↔ Cu

(At equilibrium)

Cu2+

Cu2+

Cu

Cu2+

Cu

Cu2+

Cu2+ Cu2+

Cu 2+ + 2e ↔ Cu

Equi shift to ←

- -

-

Cu

- - -

- +

+ +

+

+ +

+ +

+

Can’t measure

Abs Potential

Ag

Ag+

Ag+

Ag+

Ag+

Ag → Ag+ + e

(Oxidation)

Ag+ + e → Ag

(Reduction)

Ag+ + e ↔ Ag

(At equilibrium)

Ag

-e

-e -e

Ag+

Ag+

Ag+

Ag+ + e ↔ Ag

Equi shift to →

+ +

+

Ag

+ + +

-


- - -

- - -

- - - - - - - -


Cu half cell (-ve) Oxidation




Ag+ + e → Ag Cu → Cu 2+ + 2e



0.46 Volt

Cu + 2Ag+ → Cu2+ + 2Ag

Anode Cathode

Cu(s) | Cu2+(aq) || Ag+

(aq)| Ag (s)

Cell diagram

Anode Cathode



electrons



Cu2+ increase ↑

NO3- flow in to balance excess Cu2+

Ag+ decrease ↓

K+ flow in to balance loss of Ag+

Cu/Ag Voltaic Cell 2 Half Cell to make a Voltaic Cell

Cu Half Cell Ag Half Cell

Ag

Ag+

Cu

Cu2+

-e -e

-

-

-

-

+

+

+

+

Standard Electrode Potential

Standard Hydrogen Electrode (SHE)

Platinum coat with Platinum oxide/black – increase surface area for adsorption H2 - catalyze equilibrium bet H2 /H+

- H2 ↔ 2H+ + 2e-

Eθ

Standard Reference electrode All Cell Potential are measured against

• Conc ( 1M) • Pressure (1 atm) • Temp (298K) • Platinum- inert electrode (sys without metal)

Standard

condition

H2 at 1 atm

Platinum

H2 gas

Pt wire

Platinum

2H+ + 2e ↔ H2

Eθ = 0V

Types of Half Cells

Metal/ Ion (M/M+)

Gas/ Ion (M/M-)

Ion/ Ion (Fe3+/Fe2+)

• Pure Zn metal • Conc (1M Zn2+) • Pressure (1 atm) • Temp (298K)

Condition Std Zn/Zn2+

Condition Std CI2/CI-

• CI2 gas • Platinum electrode • Conc (1M CI-) • Pressure (1 atm) • Temp (298K)

• Platinum electrode • Conc (1M Fe3+/Fe2+) • Pressure (1 atm) • Temp (298K)

Condition Std Fe3+/ Fe2+

Zn2+

Zn

Fe3+/Fe2+

CI-

Condition for Standard C

A

N

T

M

E

A

S

U

R

E

A

B

S

P

O

T

E

N

T

I

A

L

1

2

3

How to measure

electrode

potential ?

Pt

1M H+

Measure

Difference?

http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s23-electrochemistry.html


Std Hydrogen Electrode (SHE)

Eθ = 0V

Types of Half Cells

Metal/ Ion (M/M+)

Gas/ Ion (M/M+)

Ion/ Ion (Fe3+/Fe2+)

• Pure Zn metal • Conc (1M Zn2+) • Pressure (1 atm) • Temp (298K)

Condition Std Zn/Zn2+

Condition Std CI2/CI-

• CI2 gas • Platinum electrode • Conc (1M CI-) • Pressure (1 atm) • Temp (298K)

• Platinum electrode • Conc (1M Fe3+/Fe2+) • Pressure (1 atm) • Temp (298K)

Condition Std Fe3+/ Fe2+

Zn2+

Zn

Fe3+/Fe2+

1

2

3

Connect to SHE

Connect to SHE

Connect to SHE

Eθ = 0V

Eθ = 0V

Eθ = -0.76V

Standard electrode potential Zn/Zn2+ = -0.76V

Eθ cell = -0.76V

Eθ = +0.77V

Eθ = +1.35V

Standard electrode potential Fe3+/Fe2+ = +0.77V

Eθ cell = +0.77V

Standard electrode potential CI2 /CI- = +1.35V

Eθ cell = +1.35V

Eθ= -0.76V

Eθ= +0.77V

Eθ= +1.35V

2 Half Cell with SHE as reference electrode

CI-

Pt

+

+

+

Pt


Std Electrode Potential diff systems

Eθ = 0V

Eθ = 0V

Eθ = 0V

Eθ = -0.76V

Standard electrode potential Zn/Zn2+ = -0.76V

Eθ cell = -0.76V

Eθ = +0.77V

Eθ = +1.35V

Standard electrode potential Fe3+/Fe2+ = +0.77V

Eθ cell = +0.77V

Standard electrode potential CI2 /CI- = +1.35V

Eθ cell = +1.35V

Eθ= -0.76V

Eθ= +0.77V

Eθ= +1.35V

STANDARD Reduction potential – Hydrogen as std

Oxidized sp ↔ Reduced sp Eθ/V

Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ 1/2H2 -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.35 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

-ve reduction

potential

+ve reduction

potential

Click here std analogy video

Click here std analogy


Compared to

H2 as std

Eθ cell/Cell Potential = EMF in volt EMF prod when half cell connect to SHE at std condition Std electrode potential written as std reduction potential

https://www.youtube.com/watch?v=0dLBwyTh9Dg

https://www.youtube.com/watch?v=0dLBwyTh9Dg

http://www.chemguide.co.uk/physical/redoxeqia/introduction.html

http://www.chemguide.co.uk/physical/redoxeqia/introduction.html




H2 half cell (+ve) Reduction

Anode Cathode

Zn(s) | Zn2+(aq) || H

+(aq) , H2(g) | Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell

(Oxidation) (Reduction)

Salt Bridge Flow

electrons

Eθcell = Eθ

(cathode) – Eθ (anode)

Eθcell = 0.00 – ( Eθ Zn )

0.76 = 0.00 - Eθ Zn Eθ Zn = -0.76V

Zn2+ + 2e ↔ Zn Eθ = ? 2H+ + 2e ↔ H2 E

θ = 0.00V

Std electrode potential as std reduction potential

Find Eθcell (use formula)

Eθcell = Eθ

(cathode) – Eθ(anode)


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ 1/2H2 + OH- -0.83

Zn2+ + 2e- ↔ Zn ????

Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13

H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ + 0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

-0.76V

+ve/high electrode potential is cathode (+) -ve/ low electrode potential is anode (-) Electrons flow from anode (- ) to cathode (+ )

Eθ Zn/H2 = 0.76V

Zn/H2

Zn

Zn2+

H+

Pt

H2

-

-

- +

-e

Zn/H2 Cell Determine Eθ cell Zn/Zn2+

Eθ value DO NOT depend on stoichiometric coefficient (Independent of stoichiometric eqn)

H2 half cell (-ve) Oxidation

Fe3+/2+ half cell (+ve) Reduction

Anode Cathode

Pt(s) | H2, H+

(aq) || Fe3+ Fe2+

| Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons



Eθcell = Eθ




Zn2+ + 2e- ↔ Zn -0.76


H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ ????? Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+0.77V


Eθ H2 /Fe3+ = 0.77V

Pt

Fe3+

H+

Pt

H2

+

+

+ - -

-e

H2 /Fe3+,Fe2+ Cell

H2 /Fe3+,Fe2+

2H+ + 2e ↔ H2 Eθ = 0.00V

Fe3+ + e ↔ Fe2+ Eθ = ????

Eθcell = Eθ


Eθcell = Eθ Fe3+ – (-0.00)

0.77 = Eθ Fe3+

Determine Eθ cell Fe 3+/Fe2+



CI2 half cell (+ve) Reduction

Anode

Pt(s) | H2, H+

(aq) || CI2 ,CI- | Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons



Eθcell = Eθ




Zn2+ + 2e- ↔ Zn -0.76


H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- ?????

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+1.35V


Eθ H2 /CI2

= 1.35V

H+

Pt

H2 - -

-e

H2 /CI2 Cell

2H+ + 2e ↔ H2 Eθ = 0.00V

CI + e ↔ CI- Eθ = ?????

Eθcell = Eθ


Eθcell = Eθ CI2 – (-0.00)

1.35 = Eθ CI2

H2 /CI2 Cell

+ Pt

CI - CI2

Determine Eθ cell H2 /CI2




Anode Cathode

Zn(s) | Zn2+(aq) || Cu2+

(aq) | Cu (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Zn/Cu Voltaic Cell

-e -e

Zn/Cu half cells

Eθcell = Eθ


Eθcell = +0.34 – (-0.76) = +1.10V

Zn 2+ + 2e ↔ Zn (anode) Eθ = -0.76V Cu2+ + 2e ↔ Cu (cathode) Eθ = +0.34V


Find Eθcell (use reduction potential) Find Eθ

cell (use formula)

Zn + Cu2+ → Zn2+ + Cu Eθ = ?????

Eθcell = Eθ


Zn 2+ + 2e ↔ Zn Eθ = -0.76V Cu2+ + 2e ↔ Cu Eθ = +0.34V

Zn ↔ Zn2+ + 2e Eθ = +0.76 Cu2+ + 2e ↔ Cu Eθ = +0.34 Zn + Cu2+ → Zn 2+ + Cu Eθ = +1.10V



Zn2+ + 2e- ↔ Zn - 0.76

Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17

Cu2+ + 2e- ↔ Cu + 0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.35 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

+

+1.10 V

Eθ Zn/Cu = 1.10V

Cu2+


-

-

-

-

Zn Cu

+

+

+

+




Anode Cathode

Zn(s) | Zn2+(aq) || Ag+

(aq) | Ag (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Zn/Ag Voltaic Cell

-e -e

Zn/Ag half cells

Eθcell = Eθ


Eθcell = +0.80 – (-0.76) = +1.56V

Zn 2+ + 2e ↔ Zn (anode) Eθ = -0.76V Ag + + e ↔ Ag(cathode) Eθ = +0.80V



cell (use formula)

Zn + Ag+ → Zn2+ + Ag Eθ = ?????

Eθcell = Eθ


Zn 2+ + 2e ↔ Zn Eθ = -0.76V Ag+ + e ↔ Ag Eθ = +0.80V

Zn ↔ Zn2+ + 2e Eθ = +0.76 2Ag++2e ↔ 2Ag Eθ = +0.80 Zn + Ag+ → Zn 2+ + Ag Eθ = +1.56V



Zn2+ + 2e- ↔ Zn - 0.76


2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77

Ag+ + e- ↔ Ag + 0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

+

+1.56 V

Ag

Eθ Zn/Ag = 1.56V

Ag+


-

-

-

-

+

+

+

+

Zn




Anode Cathode

Cu(s) | Cu2+(aq) || Ag+

(aq) | Ag (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Cu/Ag Voltaic Cell

-e -e

Cu/Ag half cells

Eθcell = Eθ


Eθcell = +0.80 – (+0.34) = +0.46V

Cu 2+ + 2e ↔ Cu (anode) Eθ = +0.34V Ag + + e ↔ Ag(cathode) Eθ = +0.80V



cell (use formula)

Cu + 2Ag+ → Cu2+ + 2Ag Eθ = ?????

Eθcell = Eθ


Cu 2+ + 2e ↔ Cu Eθ = +0.34V Ag+ + e ↔ Ag Eθ = +0.80V

Cu ↔ Cu2+ + 2e Eθ = -0.34 2Ag+ + 2e ↔ 2Ag Eθ = +0.80 Cu + 2Ag+→ Cu 2+ + 2Ag Eθ = +0.46V


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ 1/2H2 + OH- -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17

Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77

Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

+

+0.46V

Ag Cu

Cu2+

Half cell- high electrode potential is cathode (+) Half cell - low electrode potential is anode (-) Electrons flow from anode (- ) to cathode (+ )

Eθ Cu/Ag = 0.46V

Ag+

-

-

-

-

+

+

+

+


Mn half cell (-ve) Oxidation

Ni half cell (+ve) Reduction

Anode Cathode

Mn(s) | Mn2+(aq) || Ni2+

(aq) | Ni (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Mn/Ni Voltaic Cell

-e -e

Mn/Ni half cells

Eθcell = Eθ


Eθcell = -0.26 – (-1.19) = +0.93V

Mn 2+ + 2e ↔ Mn (anode) Eθ = -1.19V Ni2+ + 2e ↔ Ni (cathode) Eθ = -0.26V



cell (use formula)

Mn + Ni2+ → Mn2+ + Ni Eθ = ?????

Eθcell = Eθ


Mn 2+ + 2e ↔ Mn Eθ = -1.19V Ni2+ + 2e ↔ Ni Eθ = -0.26V

Mn ↔ Mn2+ + 2e Eθ = +1.19 Ni2+ + 2e ↔ Ni Eθ = -0.26 Mn + Ni2+ → Mn2+ + Ni Eθ = +0.93V


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19

H2O + e- ↔ 1/2H2 + OH- -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45

Ni2+ + 2e- ↔ Ni - 0.26

Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

+

+0.93 V

Eθ Mn/Ni = 0.93V

Ni2+


-

-

-

-

Ni Mn

+

+

+

+ Mn2+


Fe half cell (-ve) Oxidation

MnO4- half cell (+ve) Reduction

Anode Cathode

Fe(s) | Fe2+(aq) || MnO4

- ,H+, Mn2+ | Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Fe/MnO4- Voltaic Cell

-e -e

Fe/MnO4- half cells

Eθcell = Eθ


Eθcell = +1.51 – (-0.45) = +1.96V

Fe2+ + 2e ↔ Fe Eθ = -0.45V MnO4

- + 5e ↔ Mn2+ + 4H2O Eθ = +1.51V



cell (use formula)

5Fe + 2MnO4- + 16H+→5Fe2+ +2Mn2+ + 8H2O Eθ = ?

Eθcell = Eθ


Fe 2+ + 2e ↔ Fe Eθ = -0.45V MnO4

- + 5e ↔ Mn2+ + 4H2O Eθ = +1.51V

Fe ↔ Fe2+ + 2e Eθ = +0.45 MnO4

- +5e ↔ Mn2+ + 4H2O Eθ = +1.51 Fe + MnO4

- → Mn2+ + Fe2+ Eθ = +1.96V


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ 1/2H2 + OH- -0.83 Zn2+ + 2e- ↔ Zn -0.76

Fe2+ + 2e- ↔ Fe -0.45

Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+

+1.96V

Pt Fe

Fe2+

Eθ Fe/MnO4- = 1.96V

MnO4-

Mn2+

Using platinum electrode


-

-

-

-

+

+

+

+




Anode Cathode

Zn(s) | Zn2+(aq) || Fe3+ , Fe2+

(aq) | Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Zn/Fe3+,Fe2+ Cell

-e -e

Eθcell = Eθ


Eθcell = +0.77 – (-0.76) = +1.53V

Zn2+ + 2e ↔ Zn Eθ = -0.76V Fe3+ + e ↔ Fe2+ Eθ = +0.77V



cell (use formula)

Zn + 2Fe3+→ Zn2+ +2Fe2+ Eθ = ?

Eθcell = Eθ


Zn 2+ + 2e ↔ Zn Eθ = -0.76V Fe3+ + e ↔ Fe2+ Eθ = +0.77V

Zn ↔ Zn2+ + 2e Eθ = +0.76 2Fe3 +2e ↔ 2Fe2+ Eθ = +0.77 Zn + 2Fe3+ → Zn2+ + 2Fe2+ Eθ = +1.53V



Zn2+ + 2e- ↔ Zn -0.76


2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54

Fe3+ + e- ↔ Fe2+ + 0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+

+1.53V

Pt Zn

Zn2+


Eθ Zn/Fe3+ = 1.53V

Fe3+-

Fe2+


Zn/Fe3+,Fe2+

-

-

-

-

+

+

+

+



I2 half cell (+ve) Reduction

Anode Cathode

Zn(s) | Zn2+(aq) || I2 , I

-(aq) | Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Zn/I2 , I- Cell

-e -e

Eθcell = Eθ


Eθcell = +0.54 – (-0.76) = +1.30V

Zn2+ + 2e ↔ Zn Eθ = -0.76V I2

+ 2e ↔ 2I- Eθ = +0.54V



cell (use formula)

Zn + I2 → Zn2+ +2I- Eθ = ?

Eθcell = Eθ


Zn ↔ Zn2+ + 2e Eθ = +0.76 I2

+ 2e ↔ 2I- Eθ = +0.54 Zn + I2

→ Zn2+ + 2I- Eθ = +1.30V



Zn2+ + 2e- ↔ Zn -0.76


2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54

Fe3+ + e- ↔ Fe2+ + 0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+

+1.30V

Pt Zn

Zn2+


Eθ Zn/I2 = 1.30V

I--

I2


-

-

-

-

+

+

+

+

Zn/I2 , I-

Zn2+ + 2e ↔ Zn Eθ = -0.76V I2

+ 2e ↔ 2I- Eθ = +0.54V



H2 half cell (+ve) Reduction

Anode Cathode

Zn(s) | Zn2+(aq) || H

+(aq) , H2(g) | Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

Eθcell = Eθ


Eθcell = 0.00 – (-0.76) = +0.76V

Zn2+ + 2e ↔ Zn Eθ = -0.76V 2H+ + 2e ↔ H2 E

θ = 0.00V



cell (use formula)

Zn + 2H+→ Zn2+ + H2 Eθ = ?

Eθcell = Eθ


Zn 2+ + 2e ↔ Zn Eθ = -0.76V 2H+ + 2e ↔ H2 E

θ = 0.00V

Zn ↔ Zn2+ + 2e Eθ = +0.76 2H+ +2e ↔ H2

Eθ = 0.00 Zn + 2H+ → Zn2+ + H2 Eθ = +0.76V



Zn2+ + 2e- ↔ Zn -0.76


H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ + 0.77


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+

+0.76V


Eθ Zn/H2 = 0.76V

Using platinum electrode/H2

Zn/H2

Zn

Zn2+

H+

Pt

H2

-

-

- +

-e

Zn/H2 Cell




Anode Cathode

Pt(s) | H2, H+

(aq) || Ag+(aq) | Ag (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

H2/Ag Cell

Eθcell = Eθ


Eθcell = +0.80 – (-0.00) = +0.80V

2H+ + 2e ↔ H2 Eθ = 0.00V

Ag+ + e ↔ Ag Eθ = +0.80V



cell (use formula)

H2 + 2Ag+ → 2H+ + 2Ag Eθ = ?

Eθcell = Eθ


H2 ↔ 2H+ + 2e Eθ = +0.00 2Ag+ +2e ↔ 2Ag Eθ = +0.80 H2 + 2Ag+ → 2H+ + 2Ag Eθ = +0.80V



Zn2+ + 2e- ↔ Zn -0.76


H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ + 0.77


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+

+0.80V


Eθ H2 /Ag = 0.80V


H2/Ag

Ag

Ag+

H+

Pt

H2

2H+ + 2e ↔ H2 Eθ = 0.00V

Ag+ + e ↔ Ag Eθ = +0.80V

+

+

+ - -

-e




Anode Cathode

Pt(s) | H2, H+

(aq) || Fe3+ Fe2+

| Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons



cell (use formula)

H2 + 2Fe3+ → 2H+ + 2Fe 2+ Eθ = ?

Eθcell = Eθ


H2 ↔ 2H+ + 2e Eθ = +0.00 2Fe3+ +2e ↔ 2Fe2+ Eθ = +0.77 H2 + 2Fe3+ → 2H+ + 2Fe2+ Eθ = +0.77V



Zn2+ + 2e- ↔ Zn -0.76


H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F +2.87

+

+0.77V


Eθ H2 /Fe3+ = 0.77V


Pt

Fe3+

H+

Pt

H2

+

+

+ - -

-e

H2 /Fe3+,Fe2+ Cell

H2 /Fe3+,Fe2+

2H+ + 2e ↔ H2 Eθ = 0.00V

Fe3+ + e ↔ Fe2+ Eθ = +0.77V 2H+ + 2e ↔ H2 E

θ = 0.00V Fe3+ + e ↔ Fe2+ Eθ = +0.77V

Eθcell = Eθ


Eθcell = +0.77– (-0.00) = +0.77V



CI2 half cell (+ve) Reduction

Anode Cathode

Pt(s) | H2, H+

(aq) || CI2 ,CI- | Pt (s)

Cell diagram

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons



cell (use formula)

CI2 + H2 → 2CI- + 2H+ Eθ = ?

Eθcell = Eθ


H2 ↔ 2H+ + 2e Eθ = +0.00 CI2

+2e ↔ 2CI- Eθ = +1.35 H2 + CI2

→ 2H+ + 2CI- Eθ = +1.35V



Zn2+ + 2e- ↔ Zn -0.76


H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33

1/2CI2 + e- ↔ CI- +1.35 MnO4

- + 8H+ + 5e- ↔ Mn2+ +1.51 1/2F2 + e- ↔ F +2.87

+

+1.35V


Eθ H2 /CI2

= 1.35V



H+

Pt

H2 - -

-e

H2 /CI2 Cell

2H+ + 2e ↔ H2 Eθ = 0.00V

CI + e ↔ CI- Eθ = +1.35V

Eθcell = Eθ


Eθcell = +1.35 – (-0.00) = +1.35V

H2 /CI2 Cell

2H+ + 2e ↔ H2 Eθ = 0.00V

CI + e ↔ CI- Eθ = +1.35V

+ Pt

CI - CI2


STANDARD Reduction potential – H2 as std


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ H2+OH- -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F- +2.87

-ve reduction

potential

+ve reduction

potential

Compared to

H2 as std

Eθ cell/Cell Potential = EMF in volt EMF when half cell connect to SHE std condition Std potential written as std reduction potential

TOP right • High ↑ tendency lose e • Li → Li + + e

• Eθ Li = +3.04V • STRONG reducing Agent •Oxi favourable (Eθ =+ve)

STRONG

Reducing Agent

WEAK

Reducing Agent

BOTTOM right • Low ↓ tendency lose e • F - → 1/2F2 + e

• Eθ F2 = - 2.87V • WEAK reducing Agent •Oxi NOT favourable (Eθ =-ve)

WEAK

Oxidizing Agent

STRONG

Oxidizing Agent

TOP left • Low ↓ tendency gain e • Li+ + e → Li

• Eθ Li= - 3.04V • WEAK oxidizing Agent • Red NOT favourable (Eθ =-ve)

BOTTOM left • High ↑ tendency gain e • F2 + 2e → 2F-

• Eθ F2= +2.87V • STRONG oxidizing Agent •Red favourable (Eθ =+ve)

О

О

О

О


STANDARD Reduction potential – H2 as std



2- + 4H+ + 2e- ↔ H2SO3 +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F - +2.87

Eθ cell/Cell Potential = EMF in volt EMF when half cell connect to SHE std condition Std potential written as std reduction potential


• Eθ Li = +3.04V • STRONG reducing Agent •Oxi favourable (Eθ =+ve)

STRONG

Reducing Agent

STRONG

Oxidizing Agent


• Eθ F2= +2.87V • STRONG oxidizing Agent •Red favourable (Eθ =+ve)

Li → Li + + e Eθ Li = +3.04V

1/2F2 + e → F- Eθ F2 = + 2.87V

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2-+14H+ +6e- ↔ 2Cr3+ +7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F - +2.87

-ve

potential

+ve

potential

Uses of Standard Electrode Potential (SEP) Data 1

TOP left • Low ↓ tendency gain e • Li+ + e → Li

• Eθ Li= - 3.04V • Red NOT favourable (Eθ =-ve)

WEAK

Oxidizing

Agent

STRONG

Oxidizing

Agent

О


• Eθ Li = +3.04V •Oxi favourable (Eθ =+ve)

STRONG

Reducing

Agent О

WEAK

Reducing

Agent


• Eθ F2= +2.87V •Red favourable (Eθ =+ve)

О

BOTTOM right • Low ↓ tendency lose e • F - → 1/2F2 + e

• Eθ F2 = - 2.87V •Oxi NOT favour (Eθ =-ve)

О

Relative strength of Oxidizing/Reducing Agent

Eθ = +ve SEP ↓

Strong oxidizing ↓

Weak reducing agent ↓

F2 strongest oxidizing agent

↓ F- ion weakest reducing agent

Eθ = -ve SEP ↓

Weak oxidizing ↓

Strong reducing agent ↓

Li+ ion weakest oxidizing agent

↓ Li metal strongest

reducing agent

Reaction to happen ↓

1 Oxidizing + 1 Reducing agent (Strong) (Strong)

from both side

Reaction NEVER happen ↓

TWO Oxidizing agent from same sides

or TWO Reducing agent from same sides


Li+ + e- ↔ Li -3.04 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ H2+OH- -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 1/2F2 + e- ↔ F - +2.87


TOP left • Low ↓ tendency gain e • Na+ + e → Na

• Eθ Na = - 2.71V • Red NOT favourable (Eθ =-ve)

WEAK

Oxidizing

Agent

STRONG

Oxidizing

Agent


• Eθ Li = +3.04V •Oxi favourable (Eθ =+ve)

STRONG

Reducing

Agent

WEAK

Reducing

Agent


• Eθ F2= +2.87V •Red favourable (Eθ =+ve)

BOTTOM right • Low ↓ tendency lose e • Ag → Ag+ + e

• Eθ Ag = - 0.80V •Oxi NOT favour (Eθ =-ve)

О


О

О

Rxn feasible

Rxn not feasible

Rxn not feasible

Rxn feasible О



from both side


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 Pb2+ + 2e- ↔ Pb -0.13 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.33 1/2CI2 + e- ↔ CI- +1.36 1/2F2 + e- ↔ F - +2.87


WEAK

Oxidizing

Agent

STRONG

Reducing

Agent


О

Z sign

Zn ↔ Zn2+ + 2e Eθ = +0.76V Sn2+ + 2e ↔ Sn Eθ = -0.14V Zn + Sn2+→Zn2+ + Sn Eθ = +0.62V

Rxn bet Zn + Sn2+

Will it happen ?

Eθ = +0.62V +ve (spontaneous)

О

О

О

Z sign



from both side

Rxn bet CI2 + I-

Will it happen ?

2I- ↔ I2 + 2e Eθ = -0.54V CI2 + 2e ↔ 2CI- Eθ = +1.36V CI2 + 2I-→ 2CI- + I2

Eθ = +0.82V


Zn CI2

Both gaining electron NON spontaneous


K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Mn2+ + 2e- ↔ Mn -1.19 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 Pb2+ + 2e- ↔ Pb -0.13 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +7H2O +1.33 CI2 + e- ↔ CI- +1.36 1/2F2 + e- ↔ F - +2.87


WEAK

Oxidizing

Agent

STRONG

Oxidizing

Agent

STRONG

Reducing

Agent

WEAK

Reducing

Agent


О

О

Rxn bet CI2 + I2

Will it happen ?

О

Rxn NEVER happen ↓ TWO Oxidizing agent from same sides

Rxn NEVER happen ↓ TWO Reducing agent from same sides

Rxn bet Zn + Sn

Will it happen ?

Both losing electron NON spontaneous

О

Rxn NEVER happen ↓

1 Oxidizing + 1 Reducing agent (WEAK) (WEAK)

from both side

Rxn bet Mg + K +

Will it happen ?

О

О

Eθ = -ve -ve (Non spontaneous)



Anode Cathode

Zn(s) | Zn2+(aq) || Cu2+

(aq) | Cu (s)

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

-e -e

Zn/Cu half cells

Eθcell = Eθ


Eθcell = +0.34 – (-0.76) = +1.10V

Zn 2+ + 2e ↔ Zn (anode) Eθ = -0.76V Cu2+ + 2e ↔ Cu (cathode) Eθ = +0.34V



cell (use formula)

Zn + Cu2+ → Zn2+ + Cu Eθ = ?????

Eθcell = Eθ


Zn 2+ + 2e ↔ Zn Eθ = -0.76V Cu2+ + 2e ↔ Cu Eθ = +0.34V

Zn ↔ Zn2+ + 2e Eθ = +0.76 Cu2+ + 2e ↔ Cu Eθ = +0.34 Zn + Cu2+ → Zn 2+ + Cu Eθ = +1.10V



Zn2+ + 2e- ↔ Zn - 0.76


2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17

Cu2+ + 2e- ↔ Cu + 0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.35 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

+

+1.10 V

Eθ Zn/Cu = 1.10V

Cu2+

-

-

-

-

Zn Cu

+

+

+

+


Find Eθ using std electrode potential data for Zn/Cu half cell



Anode Cathode

Cu(s) | Cu2+(aq) || Ag+

(aq) | Ag (s)

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

-e -e

Eθcell = Eθ


Eθcell = +0.80 – (+0.34) = +0.46V

Cu 2+ + 2e ↔ Cu (anode) Eθ = +0.34V Ag + + e ↔ Ag(cathode) Eθ = +0.80V



cell (use formula)

Cu + 2Ag+ → Cu2+ + 2Ag Eθ = ?????

Eθcell = Eθ


Cu 2+ + 2e ↔ Cu Eθ = +0.34V Ag+ + e ↔ Ag Eθ = +0.80V

Cu ↔ Cu2+ + 2e Eθ = -0.34 2Ag+ + 2e ↔ 2Ag Eθ = +0.80 Cu + 2Ag+→ Cu2+ + 2Ag Eθ = +0.46V


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ 1/2H2 -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17

Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 1/2I2 + e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

+

+0.46V

Ag Cu

Cu2+

Eθ Cu/Ag = 0.46V

Ag+

-

-

-

-

+

+

+

+


Find Eθ using std electrode potential data for Cu/Ag half cell

Mn half cell (-ve) Oxidation

Ni half cell (+ve) Reduction

Anode Cathode

Mn(s) | Mn2+(aq) || Ni2+

(aq) | Ni (s)

Anode Cathode

Half Cell Half Cell


Salt Bridge Flow

electrons

-e -e

Eθcell = Eθ


Eθcell = -0.26 – (-1.19) = +0.93V

Mn 2+ + 2e ↔ Mn (anode) Eθ = -1.19V Ni2+ + 2e ↔ Ni (cathode) Eθ = -0.26V



cell (use formula)

Mn + Ni2+ → Mn2+ + Ni Eθ = ?????

Eθcell = Eθ


Mn 2+ + 2e ↔ Mn Eθ = -1.19V Ni2+ + 2e ↔ Ni Eθ = -0.26V

Mn ↔ Mn2+ + 2e Eθ = +1.19 Ni2+ + 2e ↔ Ni Eθ = -0.26 Mn + Ni2+ → Mn2+ + Ni Eθ = +0.93V


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19

H2O + e- ↔ 1/2H2 + OH- -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45

Ni2+ + 2e- ↔ Ni - 0.26

Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4


2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F +2.87

+

+0.93 V

Eθ Mn/Ni = 0.93V

Ni2+

-

-

-

-

Ni Mn

+

+

+

+ Mn2+

2 Uses of Standard Electrode Potential (SEP) Data

Find Eθ using std electrode potential data for Mn/Ni half cell

Eθ = -0.20V -ve (NON spontaneous)



from both side


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 Cu+ + e- ↔ Cu +0.52 I2 + 2e- ↔ I- +0.54 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + e- ↔ F - +2.87


WEAK

Oxidizing

Agent

STRONG

Oxidizing

Agent

STRONG

Reducing

Agent

WEAK

Reducing

Agent

О

Z Zn ↔ Zn2+ + 2e Eθ = +0.76 Sn2+ + 2e ↔ Sn Eθ = -0.14 Zn + Sn2+→ Zn2+ + Sn Eθ = +0.62V

Rxn bet Zn + Sn2+

Will it happen ?




from both side

Rxn bet Cu2+ +I-

Will it happen ?

О

Rxn feasible

О О

2I- ↔ I2 + 2e Eθ = -0.54 Cu2+ + 2e ↔ Cu Eθ = +0.34 2I- + Cu2+→ Cu + I2

Eθ = -0.20V


Rxn not feasible

Zn(s) | Zn2+(aq) || Sn2+

(aq) | Sn (s)


Anode Cathode


Eθcell = Eθ


Eθcell = -0.14 – (-0.76) = +0.62V


Pt(s) | I-, I2 || Cu2+

(aq) | Cu (s)

Anode Cathode



Eθcell = Eθ


Eθcell = +0.34 – (+0.54) = -0.20V

Determine spontaneity rxn. Will it HAPPEN ?




from both side


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 Pb2+ + 2e- ↔ Pb -0.13 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2SO3 +0.17 Cu2+ + 2e- ↔ Cu +0.34 I2 + 2e- ↔ I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +7H2O +1.33 1/2CI2 + e- ↔ CI- +1.36 1/2F2 + e- ↔ F - +2.87


WEAK

Oxidizing

Agent

STRONG

Oxidizing

Agent

STRONG

Reducing

Agent

WEAK

Reducing

Agent

О

Z

Zn ↔ Zn2+ + 2e Eθ = +0.76 Cu2+ + 2e ↔ Cu Eθ = +0.34 Zn + Cu2+→ Zn2+ +Cu Eθ = +1.10V

Rxn bet Zn + Cu2+

Will it happen ?




from both side

Rxn bet I2 +CI-

Will it happen ?

О Rxn feasible О

О

2CI- ↔ CI2 + 2e Eθ = -1.36 I2

+ 2e ↔ 2I- Eθ = +0.54 I2 + 2CI- → 2I- + CI2

Eθ = -0.82V


Rxn not feasible

Zn(s) | Zn2+(aq) || Cu2+

(aq) | Cu (s)


Anode Cathode


Eθcell = Eθ


Eθcell = 0.34 – (-0.76) = +1.10V


Pt(s) | CI-, CI2 || I2 I-

| Pt (s)

Anode Cathode



Eθcell = Eθ


Eθcell = +0.54 – (+1.36) = -0.82V




Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Mg 2+ + 2e- ↔ Mg -2.37 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 H2O + e- ↔ H2 + OH- -0.83 Zn2+ + 2e- ↔ Zn -0.76 Fe2+ + 2e- ↔ Fe -0.45 Ni2+ + 2e- ↔ Ni -0.26 Sn2+ + 2e- ↔ Sn -0.14 H+ + e- ↔ 1/2H2 0.00 Cu2+ + e- ↔ Cu+ +0.15 SO4

2- + 4H+ + 2e- ↔ H2S +0.17 Cu2+ + 2e- ↔ Cu +0.34 Cu+ + e- ↔ Cu +0.52 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 1/2O2 + 2H+ +2e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.33 1/2CI2 + e- ↔ CI- +1.36 1/2F2 + e- ↔ F - +2.87


WEAK

Oxidizing

Agent

STRONG

Oxidizing

Agent

STRONG

Reducing

Agent

WEAK

Reducing

Agent

Cu ↔ Cu2+ + 2e Eθ = -0.34 2H+ + 2e ↔ H2 Eθ = +0.00 Cu + 2H+→ Cu2+ +H2

Eθ = -0.34V

Rxn bet Cu + H+

Will it happen ?



1 Oxidizing + 1 Reducing agent (WEAK) (WEAK) from both side

Rxn bet Fe3+ +CI-

Will it happen ?

О

О

О

2CI- ↔ CI2 + 2e Eθ = -1.36 2Fe3+ + 2e ↔ 2Fe2+ Eθ = +0.77 2Fe3+ + 2CI-→2Fe2++CI2

Eθ = -0.59V


Rxn not feasible

Cu(s) | Cu2+(aq) || H

+ H2 | Pt (s)


Anode Cathode


Eθcell = Eθ


Eθcell = 0.00 – (+0.34) = -0.34V

Eθ = -0.34V -ve (spontaneous)

Pt(s) | CI-, CI2 || Fe3+ ,Fe2+ |Pt (s)

Anode Cathode



Eθcell = Eθ


Eθcell = +0.77 – (+1.36) = -0.59V

О

Rxn not feasible


1 Oxidizing + 1 Reducing agent (WEAK) (WEAK) from both side


Eθ value DO NOT depend surface area of metal electrode. EMF = Energy per unit charge. (Joule)/C EMF 10v = 10J energy released by 1C of charge flowing = 100J energy released by 10C of charge flowing Eθ – intensive property– independent of amt – ratio energy/charge

Increasing surface area metal will NOT increase EMF

Eθ Zn/Cu = 1.10V

Surface area exposed 10 cm2 Total charges 100C leave electrode EMF = 1.10V = 1.1 J energy for 1 C (charges leaving) 1C release 1.1J energy 100 C release 110 J energy Voltmeter measure energy for 1C – 110J/100C – 1.1V EMF no change

Current – measured in Amperes or Coulombs per second 1A = 1 Coulomb charge pass through a point in 1 second = 1C/s 1 Coulomb charge (electron) = 6.28 x 10 18 electrons passing in 1 second 1 electron/proton carry charge of – 1.6 x 10 -19 C ( very small) 6.28 x 10 18 electron carry charge of - 1 C

ond

electron

ond

CoulombA

sec.1

.1028.6

sec1

11

18

Surface area increase ↑

Total Energy increase ↑

Total Charge increase ↑ Current increase ↑

BUT EMF remain SAME EMF = (Energy/charge)

t

QI

tIQ

Q up ↑ – I up ↑

100C flow

110J released

VEMF

EMF

eCh

EnergyEMF

10.1

100

110

arg

Surface area exposed 10 cm2

Surface area exposed 100cm2

Surface area exposed 100 cm2 Total charges 1000C leave electrode EMF = 1.10V = 1.1 J energy for 1 C (charges leaving) 1C release 1.1J energy 1000 C release 1100 J energy Voltmeter measure energy for 1C – 1100J/1000C – 1.1V EMF no change

VEMF

EMF

eCh

EnergyEMF

10.1

1000

1100

arg

Eθ Zn/Cu = 1.10V

1000C flow

1100J released

t

QI

t

QI

Iron rust in presence of water + oxygen

Iron galvanized/coated with zinc.


Zn2+ + 2e- ↔ Zn - 0.76 Fe2+ + 2e- ↔ Fe -0.44 O2 + 2H2O + 4e ↔ 4OH- +0.40

Iron rusting Rusting Process happen

Eθ/V

Fe2+ + 2e- ↔ Fe -0.44 O2 + 2H2O + 4e ↔ 4OH- +0.40 O2 + 4H+ + 4e ↔ 2H2O + 1.23

H2O + O2 less reactive (cathode region) – reduction – gain e

Fe more reactive (anode region) – oxidation - lose e

Oxidation Reduction

Fe2+ + 2e- ↔ Fe -0.44 O2 +2H2O+4e ↔ 4OH- +0.40

Fe ↔ Fe2+ + 2e Eθ = +0.44 O2+2H2O+4e ↔ 4OH- Eθ = +0.40 2Fe +O2

+2H2O→2Fe2++4OH- Eθ = +0.84V


О О

Dissolve O2

in water

Dissolve O2

in acid

How galvanizing reduces rusting

Iron Galvanized

with Zn

Iron/Steel Galvanized

with tin

Zn more reactive – lose e instead of Fe

Zn as Sacrificial metal/ Cathodic Protection

Electron flow to O2/H2O region

Prevent Fe rusting/lose e

O2 gain e

Fe

O2 + 2H2O + 4e ↔ 4OH-

flow e-

Zn oxidation/lose e

Zn2+ + 2e- ↔ Zn -0.76 O2 +2H2O+4e ↔ 4OH- +0.40

Zn lose e- (Stronger RA)

Zn ↔ Zn2+ + 2e Eθ = +0.76 O2+2H2O+4e ↔ 4OH- Eθ = +0.40 2Zn +O2

+2H2O→2Zn2++4OH- Eθ = +1.16V

Eθ = +1.16 +ve (spontaneous)

water

О О

Anodic region

Cathodic region

Zn Zn

Fe Fe Fe


Iron rust in presence of water + oxygen

Iron can coated with tin widely used in canning Tin corrodes less readily than iron (protect iron)


Fe2+ + 2e- ↔ Fe -0.44 Sn2+ + 2e- ↔ Sn -0.14 O2 + 2H2O + 4e ↔ 4OH- +0.40

Iron rusting

If tin coat broken, iron rust faster as it will displace tin ions from its solution Will iron rust spontaneously, if Sn2+ (tin ions) are formed.

Rusting Process happen

Eθ/V

Fe2+ + e- ↔ Fe -0.44 O2 + 2H2O + 4e ↔ 4OH- +0.40 O2 + 4H+ + 4e ↔ 2H2O + 1.23

H2O + O2 less reactive (cathode region) – reduction – gain e

Fe more reactive (anode region) – oxidation - lose e

Oxidation Reduction

Fe2+ + 2e- ↔ Fe -0.44 O2 +2H2O+4e ↔ 4OH- +0.40


+2H2O→4Fe2++4OH- Eθ = +0.84V


О О

Dissolve O2

in water

How coating reduces rusting Iron/Steel coated with tin/Sn

BUT if it is exposed - Fe will rust Fe more reactive Sn

Tin/Sn protect Fe metal

Electron flow Fe to O2/H2O region

water

Fe oxidation/lose e

flow e-

O2 + 2H2O + 4e ↔ 4OH-

Iron metal

water O2 gain e

Sn Sn2+


Fe2+ + 2e- ↔ Fe -0.44 Sn2+ + 2e- ↔ Sn -0.14 O2 + 2H2O + 4e ↔ 4OH- +0.40


+2H2O→4Fe2++4OH- Eθ = +0.84V

Fe ↔ Fe2+ + 2e Eθ = +0.44 Sn2+ + 2e ↔ Sn Eθ = -0.14 Fe + Sn2+ → Fe2++ Sn Eθ = +0.30V


О О

О О

Sn Sn Sn

Fe Fe Fe Fe

State which is able to convert Fe2+ to Fe3+


AI3+ + 3e- ↔ AI -1.66 I2 + 2e- ↔ 2I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 H2O2 + 2H+ + 2e ↔ 2H2O +1.07 Co3+ + e ↔ Co2+ +1.51

2Fe2+ ↔ 2Fe3+ + 2e Eθ = -0.77 H2O2 + 2H+ + 2e ↔ 2H2O Eθ =+1.07 2Fe2+ + H2O2

+ 2H+ → 2Fe3+ + 2H2O Eθ = +0.30V


Fe2+ ↔ Fe3+ + e Eθ = -0.77 Co3+ + e ↔ Co 2+ Eθ =+1.51 Fe2+ + Co3+ → Fe3+ + Co2+ Eθ = +0.74V


Eθ cell = EMF in V (std condition) Eθ = Show ease/tendency of species to accept/lose electron Eθ = +ve std electrode potential = stronger oxidizing agent – weaker reducing agent – accept e Eθ = - ve std electrode potential = stronger reducing agent - weaker oxidizing agent – lose e EMF when half cell connect to SHE std condition Std potential written as std reduction potential Eθ value DO NOT depend on stoichiometric coefficient. EMF = Energy per unit charge. (Joule)/C EMF 10v = 10J energy released by 1C of charge flowing = 100J energy released by 10C of charge flowing Eθ , Std electrode potential – intensive property – not dependent on amt – ratio energy/charge Eθ = +ve suggest rxn feasible, does not tell rate, feasible but may be slow, give no indication rate Eθ = +ve = Energetically feasible but kinetically non feasible

E = ↑ +ve ↑ (OA)


Fe3+ + e- ↔ Fe2+ +0.77 H2O2 +2H++2e ↔ 2H2O +1.07


Fe3+ + e- ↔ Fe2+ +0.77 Co3+ + e ↔ Co2+ +1.51

Stronger OA

Strongest OA

Redox Question

Aluminium air battery

Excellent Zn/Cu gravity cell for IA

Zinc air battery

Videos on battery making

http://www.youtube.com/watch?v=_FxIzMwOF00&feature=relmfu

http://www.youtube.com/watch?v=OcGWbt1mcrc&feature=plcp&context=C3b22d58UDOEgsToPDskI9rxobZyZ1mrYIjJfH9eSD

Arrange the species in order of increasing oxidizing/reducing strength


Zn2+ + 2e- ↔ Zn -0.76 Br2 + 2e- ↔ 2Br- +1.07 I2 + 2e- ↔ 2I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

Oxidizing agent (OA) MnO4

_ > Br2 > Fe3+ > I2 > Zn2+

Reducing agent (RA) Zn > I- > Fe 2+ > Br- > Mn2+

Arrange in order of increasing reducing strength. (Strongest reducing agent)

Redox Questions

1 2

E = most +ve ↑ strongest OA

E = most -ve ↑ strongest RA


Zn2+ + 2e- ↔ Zn -0.76 I2 + 2e- ↔ 2I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Br2 + 2e- ↔ 2Br- +1.07 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

arrange increasing ↑ E value

E = ↑ +ve ↑ (OA)

Eθ/V

X 3+ + 3e- ↔ X -1.56 Y 2+ + 2e- ↔ Y -2.70 Z 2+ + 2e- ↔ Z +0.90

E = ↑ -ve ↑(RA)

E = most -ve ↑ strongest RA

Reducing agent Y > X > Z

arrange increasing ↑ E value

Eθ/V

Y 2+ + 2e- ↔ Y -2.70 X 3+ + 3e- ↔ X -1.56 Z 2+ + 2e- ↔ Z +0.90

E = ↑ -ve ↑ (RA)

4 3

Oxidized sp ↔ Reduced sp Eθ/V Ti2+ + 2e- ↔ Ti -1.63 2H+ + 2e- ↔ H2 0.00

Rxn bet Ti + H+

Will it happen ?

Ti ↔ Ti2+ + 2e Eθ = +1.63 2H+ + 2e ↔ H2 E

θ = 0.00 Ti + 2H+ → Ti2+ + H2

Eθ = +1.63V Eθ = +1.63V +ve (spontaneous)

What happen when gold added to acid

Oxidized sp ↔ Reduced sp Eθ/V 2H+ + 2e- ↔ H2 0.00 Au3+ + 3e ↔ Au +1.58

Rxn bet Au + H+

Will it happen ?

What happen when titanium added to acid

2Au ↔ 2Au3+ + 6e Eθ = -1.58 6H+ + 6e ↔ 3H2 E

θ = 0.00 2Au + 6H+ → 2Au3+ + 3H2

Eθ = -1.58V Eθ = -1.58V -ve ( NON spontaneous)

acid acid

Redox Question

6 Predict if manganate will oxidize chloride ion?

MnO2 + 4H+ + 2CI- → Mn2+ + 2H2O + CI2 Eθ = ?

5

MnO2 +4H+ + 2e- ↔ Mn2+ + 2H2O +1.23

1/2CI2 + e- ↔ CI- +1.36

2CI- ↔ CI2 + 2e Eθ = -1.36 MnO2 + 4H+ + 2e ↔ Mn2+ + 2H2O Eθ = +1.23 MnO2 + 4H++2CI- → Mn2++2H2O+CI2 E

θ= -0.13V



Cr2O72-+ 14H+ + 6e- ↔ 2Cr3+ + 7H2O +1.33

MnO2 +4H+ + 2e- ↔ Mn2+ + 2H2O +1.23

1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

Predict if MnO4- able to oxidize aq CI- to CI2

2MnO4 + 16H+ + 10CI- → 2Mn2+ + 8H2O + 5CI2

E = ↑ +ve ↑ (OA)

О

О


Cr2O72-+ 14H+ + 6e- ↔ 2Cr3+ + 7H2O +1.33

MnO2 +4H+ + 2e- ↔ Mn2+ + 2H2O +1.23

1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

О

О

2CI- ↔ CI2 + 2e Eθ = -1.36 MnO4

- + 8H+ + 5e ↔ Mn2+ + 4H2O Eθ = +1.51 2MnO4 + 16H++10CI- → 2Mn2++8H2O+5CI2 E

θ= +0.15V

1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51


Predict if iron react with HCI a) absence air

Which is stronger OA ?

Fe ↔ Fe2+ + 2e Eθ = +0.44 2H+ + 2e ↔ H2 E

θ = 0.00V Fe + 2H+ → Fe2+ + H2

Eθ = +0.44V



Fe2+ + 2e- ↔ Fe -0.44 2H+ + 2e- ↔ H2 0.00 O2 +2H2O+4e ↔ 4OH- +0.40


+2H2O→2Fe2++4OH- Eθ = +0.84V

Predict if iron react with HCI b) presence of air

Fe2+ + 2e- ↔ Fe -0.44 2H+ + 2e- ↔ H2 0.00

О О

Fe2+ + 2e- ↔ Fe -0.44 O2 +2H2O+4e ↔ 4OH- +0.40

О О


Fe2+ + 2e- ↔ Fe -0.44 2H+ + 2e- ↔ H2 0.00 O2 +2H2O+4e ↔ 4OH- +0.40


Iron rusting

E = ↑ +ve ↑ (OA)

ib chemistry on standard reduction potential, standard hydrogen electrode and electrochemical series

Education

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e cu zn zn

e zn reduction zn

ve zn2 zn zn

e oxidation zn

e oxidation cu2

e cu reduction cu2

loss of cu2 zn cu