ib chemistry on electrolysis and faraday's law

http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

Tutorial on Electrolysis and Faraday’s Law.

Types voltaic cell

Conversion electrical energy to chemical energy

Electrochemistry

Electrolytic cellVoltaic cell

NH4CI and ZnCI2

Chemical and electrical energy

Redox rxn (Oxidation/reduction)

Movement electronProduce electricity

Conversion chemical energy to electrical energy

Electrodes – different metal (Half cell) Electrodes – same metal (Half cell)

Chemical rxn

Electric current

Daniell cell Alkaline cellDry cell Nickel cadmium cell

Primary cell (Non rechargeable)

MnO2 and KOH

Secondary cell (Rechargeable)

Conversion electrical to chemical energy

Electrochemistry

Electrolytic cellVoltaic cell

Conversion chemical to electrical energy

Cathode (+ve) - Reduction Cathode (-ve) - Reduction

Vs

Electron flow from anode (-ve) to cathode (+ve) electrode Electron flow from anode (+ve) to cathode (-ve) electrode

Anode (-ve)

Spontaneous rxn Non Spontaneous rxn

Anode (-ve) – Oxidation Anode (+ve) – Oxidation

++

О ООО

- -

Zn → Zn 2+ + 2e (oxidized)

Cu2+ + 2e → Cu (reduced)

Zn2+

Zn2+

Zn2+

Zn2+----→ + +

+Cu2+

Cu2+

Cu2+

-e-e

++

+ -- -

X- X + -e→(oxidized)

X-X-

X-

Anode (+ve)

Cathode (-ve)

Cathode (+ve)

-e

-e

Y+ + e- Y→(reduced)

Y+Y+

Y+-e-e

-e

-e

Anode Cathode

Voltaic Cell Electrolytic Cell

Anode Oxidation Negative (-ve) Oxidation Positive (+ve)

Cathode Reduction Positive (+ve) Reduction Negative (-ve)

Cation (+ve ion) to cathode (-ve)Anion (-ve ion) to anode (+ve)

Zn → Zn 2+ + 2e


Electrochemistry


Cathode (-ve) Reduction

Vs

Electron flow from anode (-ve) to cathode (+ve) electrode Electron flow from anode (+ve) to cathode (-ve) electrode

Anode (-ve)


Anode (+ve) Oxidation

+

ОО-

Zn → Zn 2+ + 2e (oxidized)

Cu2+ + 2e → Cu (reduced)

Zn2+

Zn2+

Zn2+

Zn2+

----→ + +

+Cu2+

Cu2+

Cu2+

-e-e +

++

---

2Br- Br→ 2 + 2e-(oxidized)

Br-

Br-

Br-

Anode (+ve)

Cathode (-ve)Cathode

(+ve)

-e

-e

Pb2+ + 2e- Pb→(reduced)

Pb2+

-e-e

-e

Cation (+ve ion) to cathode (-ve)Anion (-ve ion) to anode (+ve)

1.10Volt -e -e

----

++++

Anode Cathode

Zn half cell (-ve)Oxidation

Cu half cell (+ve)Reduction

Cu2+ + 2e → Cu

Zn + Cu2+ → Zn2+ + Cu

2Br- → Br2 + 2e

Zn/Cu Voltaic Cell PbBr2 molten Electrolytic Cell

Pb2+ + 2e → Pb

PbBr2 → Pb + Br2

Br -

Br -

Br -

Pb2+

Pb2+

Pb2+

Pb2+

Pb2+


Electrochemistry



Vs



+

ОО-

-e1.10 Volt

-e -e

----

++++

Anode Cathode

Zn/Cu Voltaic Cell PbBr2 molten Electrolytic Cell

PbBr2 Pb→ + Br2 Eθ = ???

Br -

Br -

Br -

Pb2+

Pb2+

Pb2+

Find Eθcell (use reduction potential)

Zn 2+ + 2e Zn E↔ θ = -0.76VCu2+ + 2e Cu E↔ θ = +0.34V

Cu half cell (+ve)Reduction

Zn half cell (-ve)Oxidation

Zn + Cu2+ Zn→ 2+ + Cu Eθ = ?????

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

Eθ = +1.10V+ve (spontaneous)

Pb2+ + 2e Pb E↔ θ = -0.13VBr- + e Br ↔ - Eθ = +1.07V


2Br - Br↔ 2+ 2e Eθ = -1.07Pb2+ + 2e Pb E↔ θ = -0.13Pb2+ + 2Br - Pb→ +Br2 Eθ = -1.20V

Compound broken down (LYSIS) energy needed

Eθ = -1.20V-ve (NON spontaneous)

Conversion chemical to electrical energy Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!

Discharge of ions1 Cation + 1 Anion

Electrolysis (Molten Salt)

Oxidation ← Anode (+ve) ← Anion

PbBr2 molten Electrolytic Cell

Eθ =-ve → supply +1.20v to breakdown PbBr2 Pb→ + Br2


Pb2+ + 2e Pb E↔ θ = -0.132Br - Br↔ 2+ 2e Eθ = -1.07Pb2+ + 2Br - Pb→ +Br2 Eθ = -1.20V


Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!

Cation → Cathode (-ve) → Reduction

Liquid – Pb2+ and Br- ions

+

+++++

-----

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

Cu2+ + e- Cu↔ + +0.15SO4

2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40Cu+ + e- ↔ Cu +0.521/2I2 + e- ↔ I- +0.54Fe3+ + e- ↔ Fe2+ + 0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07

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

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.511/2F2 + e- ↔ F- +2.87

Discharged Br- ion Br2 gas (brown gas seen) Discharged Pb2+ ion to Pb (grey deposit)

2Br - Br↔ 2+ 2e

Pb2+ + 2e Pb ↔


О

О

Eθ Oxidation = -1.07

Eθ Reductio

n = -0.13

Pb2+ Br -

Factor affecting ion discharged (Selective Discharge)

↓- Molten/aqueous

- Relative E values of ion- Conc ion – conc/diluted

- Nature of electrode

Inert electrode Carbon/graphite

Br -

Br -

Br -

Pb2+

Pb2+

Pb2+



CaCI2 molten Electrolytic Cell


Ca2+ + 2e Ca E↔ θ = -2.872CI - CI↔ 2+ 2e Eθ = -1.36Ca2+ + 2CI - Ca→ +CI2 Eθ = -4.23V




Liquid – Ca2+ and CI- ions

+

+++++

-----

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- Li↔ -3.04K+ + e- K↔ -2.93Ca2+ + 2e- Ca ↔ -2.87

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

2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40Cu+ + e- ↔ Cu +0.521/2I2 + e- ↔ I- +0.54Fe3+ + e- ↔ Fe2+ + 0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ + 7H2O +1.33

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.511/2F2 + e- ↔ F- +2.87

Discharged CI- ion CI2 gas (yellow gas) Discharged Ca2+ ion to Ca

2CI - CI↔ 2+ 2e

Ca2+ + 2e Ca ↔


О

О

E θ Oxidation = -1.36

Eθ R

educ

tion

= -2

.87

Ca2+ CI -

Eθ =-ve → supply +4.23v to breakdown CaCI2 Ca→ + CI2

Electrolysis (Molten Salt)


↓- Molten/aqueous




CI -

CI -

CI -

Ca2+

Ca2+

Ca2+



NaCI aqueous Electrolytic Cell

2H+ + 2e H↔ 2 Eθ = -0.834OH - 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 2H→ 2 + O2 Eθ = -2.06V




Na+ , CI- + H+ , OH- (from water)

+

+++++

-----

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- Li↔ -3.04K+ + e- K↔ -2.93Ca2+ + 2e- Ca ↔ -2.87Na+ + e- Na↔ -2.71

Al3+ + 3e- AI -1.66↔Mn2+ + 2e- Mn -1.19↔2H2O +2e- H↔ 2 + 2OH- -0.83

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

2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40Cu+ + e- ↔ Cu +0.521/2I2 + e- ↔ I- +0.54Fe3+ + e- ↔ Fe2+ + 0.77Ag+ + e- ↔ Ag +0.80

O2 + 4H+ +4e- ↔ H2O +1.23Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.331/2CI2 + e- ↔ CI- +1.36

1/2F2 + e- ↔ F- +2.87

Discharged OH- ion O2 gas Discharged H+ ion to H2 gas

О

О

Na+/H+ CI-/OH-

Eθ =-ve → supply +2.06v to breakdown NaCI H→ 2 + O2

Electrolysis (Aqueous Salt)Factor affecting ion discharged

(Selective Discharge)↓

- Molten/aqueous- Relative E values of ion- Conc ion – conc/diluted


ReductionEθ > more +ve easier gain eNa+ + e Na E↔ θ = -2.712H+ + 2e H↔ 2 Eθ = -0.832H2O +2e- H↔ 2 + 2OH- Eθ = -0.83

ОOxidation

Eθ > more +ve easier to lose e4OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.232CI- CI↔ 2 + 2e Eθ = -1.36

О


OH-

OH-

CI -

CI -

H+

H+

Na+

Na+



NaI aqueous Electrolytic Cell

2H+ + 2e H↔ 2 Eθ = -0.832I - I↔ 2 + 2e Eθ = -0.54NaI H→ 2 + I2 Eθ = -1.37V




Na+ , I- + H+ , OH- (from water)

+

+++++

-----




2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40

I2 + 2e- ↔ 2I- +0.54Fe3+ + e- ↔ Fe2+ +0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.511/2F2 + e- ↔ F- +2.87

Discharged I- ion I2 Discharged H+ ion to H2 gas

О

О

Na+/H+ I-/OH-

Eθ = -ve → supply +1.37 v to breakdown NaI H→ 2 + I2

Electrolysis (Aqueous Salt)Factor affecting ion discharged

(Selective Discharge)↓

- Molten/aqueous- Relative E values of ion- Conc ion – conc/diluted



ОOxidation

Eθ > more +ve easier to lose e2I- I↔ 2 + 2e Eθ = -0.544OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.23

О


I -

I -

OH-

OH-H+

H+

Na+

Na+



CuCI2 aqueous Electrolytic Cell

Cu2+ + 2e Cu↔ Eθ = +0.344OH- 2H↔ 2O + O2 + 4e Eθ = -1.23CuCI2 Cu + O→ 2 Eθ = -0.89V




Cu2+ , CI- + H+ , OH- (from water)

+

+++++

-----

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- Li↔ -3.04K+ + e- K↔ -2.93Ca2+ + 2e- Ca ↔ -2.87Na+ + e- Na↔ -2.71Mg 2+ + 2e- Mg ↔ -2.37Al3+ + 3e- AI -1.66↔Mn2+ + 2e- Mn -1.19↔2H2O +2e- H↔ 2 + 2OH- -0.83


2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.34

Cu+ + e- ↔ Cu +0.52I2 + 2e- ↔ 2I- +0.54Fe3+ + e- ↔ Fe2+ +0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23

1/2CI2 + e- ↔ CI- +1.36

1/2F2 + e- ↔ F- +2.87

Discharged OH- ion O2 Discharged Cu2+ ion to Cu metal

О

Cu2+/H+ CI-/OH-

Eθ = -ve → supply +0.89 v to breakdown CuCI2 Cu→ + O2

Electrolysis (Aqueous Salt)


↓- Molten/aqueous



ReductionEθ > more +ve easier gain e2H+ + 2e H↔ 2 Eθ = -0.832H2O +2e- H↔ 2 + 2OH- Eθ = -0.83Cu2+ + 2e Cu E↔ θ = +0.34 О

OxidationEθ > more +ve easier to lose e4OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.232CI- CI↔ 2 + 2e Eθ = -1.36

ОО


OH-

OH-

CI -

CI -

H+

H+

Cu2+

Cu2+



CuBr2 aqueous Electrolytic Cell

Cu2+ + 2e Cu↔ Eθ = +0.342Br- Br↔ 2 + 2e Eθ = -1.07CuBr2 Cu + Br→ 2 Eθ = -0.73V




Cu2+ , Br- + H+ , OH- (from water)

+

+++++

-----




2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.34

Cu+ + e- ↔ Cu +0.52I2 + 2e- ↔ 2I- +0.54Fe3+ + e- ↔ Fe2+ +0.77

1/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.511/2F2 + e- ↔ F- +2.87

Discharged Br- ion Br2 Discharged Cu2+ ion to Cu

О

Cu2+/H+ Br-/OH-

Eθ = -ve → supply +0.73 v to breakdown CuBr2 Cu→ + Br2



↓- Molten/aqueous




OxidationEθ > more +ve easier to lose e2Br- Br↔ 2 + 2e Eθ = -1.074OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.23


Br-

Br-

OH-

OH-

Cu2+

Cu2+

H+

H+



KI aqueous Electrolytic Cell

2H+ + 2e H↔ 2 Eθ = -0.832I- I↔ 2 + 2e Eθ = -0.54KI H→ 2+ Br2 Eθ = -1.37V




K+ , I- + H+ , OH- (from water)

+

+++++

-----

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- Li↔ -3.04K+ + e- K↔ -2.93

Na+ + e- Na↔ -2.71Mg 2+ + 2e- Mg ↔ -2.37Al3+ + 3e- AI -1.66↔Mn2+ + 2e- Mn -1.19↔2H2O +2e- H↔ 2 + 2OH- -0.83


2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40

I2 + 2e- ↔ 2I- +0.54Fe3+ + e- ↔ Fe2+ +0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.511/2F2 + e- ↔ F- +2.87

Discharged I- ion I2 Discharged H+ ion to H2

О

K+/H+ I-/OH-

Eθ = -ve → supply +1.37 v to breakdown KI H→ 2 + I2



↓- Molten/aqueous



ReductionEθ > more +ve easier gain eK+ + e K E↔ θ = -2.932H+ + 2e H↔ 2 Eθ = -0.832H2O +2e- H↔ 2 + 2OH- Eθ = -0.83

ОOxidation

Eθ > more +ve easier to lose e2I- I↔ 2 + 2e Eθ = -0.544OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.23

ОО


OH-

OH-

I -

I -

H+

H+

K+

K+



K2SO4 aqueous Electrolytic Cell

2H+ + 2e H↔ 2 Eθ = -0.834OH- 2H↔ 2O+ O2 + 4e Eθ = -1.23K2SO4

H→ 2+ O2 Eθ = -2.06V




K+ , SO42- + H+ , OH- (from water)

+

+++++

-----

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- Li↔ -3.04K+ + e- K↔ -2.93

Na+ + e- Na↔ -2.71Mg 2+ + 2e- Mg ↔ -2.37Al3+ + 3e- AI -1.66↔Mn2+ + 2e- Mn -1.19↔2H2O +2e- H↔ 2 + 2OH- -0.83


2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40I2 + 2e- ↔ 2I- +0.54Fe3+ + e- ↔ Fe2+ +0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51S2 O8

2- + 2e ↔ SO42- +2.01

1/2F2 + e- ↔ F- +2.87

Discharged OH- ion O2 Discharged H+ ion to H2

О

K+/H+ SO42-/OH-

Eθ = -ve → supply +2.06 v to breakdown K2SO4 H→ 2 + O2



↓- Molten/aqueous



ReductionEθ > more +ve easier gain eK+ + e K E↔ θ = -2.932H+ + 2e H↔ 2 Eθ = -0.832H2O +2e- H↔ 2 + 2OH- Eθ = -0.83

ОOxidation

Eθ > more +ve easier to lose e4OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.232SO4

2- S↔ 2O82- + 2e Eθ = -2.01

ОО

H2 gas

Ratio 1:2

O2 gas


OH-

OH-

SO42-

SO42-

K+

K+

H+

H+



AgNO3 aqueous Electrolytic Cell

Ag+ + e Ag E↔ θ = +0.804OH- 2H↔ 2O+ O2 + 4e Eθ = -1.23AgNO3

Ag + O→ 2 Eθ = -0.43V




Ag+ , NO3- + H+ , OH- (from water)

+

+++++

-----



2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40I2 + 2e- ↔ 2I- +0.54

Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51S2 O8

2- + 2e ↔ SO42- +2.01

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F- +2.87

Discharged OH- ion O2 Discharged Ag+ ion to Ag

О

Ag+/H+ NO3-/OH-

Eθ = -ve → supply +0.43 v to breakdown AgNO3 Ag + O→ 2



↓- Molten/aqueous



ReductionEθ > more +ve easier gain e2H+ + 2e H↔ 2 Eθ = -0.832H2O +2e- H↔ 2 + 2OH- Eθ = -0.83Ag+ + e Ag E↔ θ = +0.80

ОOxidation

Eθ > more +ve easier to lose e4OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.23NO3

- cannot be discharged


OH-

OH-

NO3-

NO3-

H+

H+

Ag+

Ag+



H2SO4 aqueous Electrolytic Cell

2H+ + 2e H↔ 2 Eθ = -0.834OH - 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 2H→ 2 + O2 Eθ = -2.06V




H+ , SO42- + H+ , OH- (from water)

+

+++++

-----




O2 + 4H+ +4e- ↔ H2O +1.23Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.331/2CI2 + e- ↔ CI- +1.36

S2 O82- + 2e ↔ SO4

2- +2.011/2F2 + e- ↔ F- +2.87

Discharged OH- ion O2 gas Discharged H+ ion to H2 gas

О

О

H+ SO42-/OH-

Eθ =-ve → supply +2.06v to breakdown H2SO4 H→ 2 + O2



↓- Molten/aqueous



ReductionEθ > more +ve easier gain e2H+ + 2e H↔ 2 Eθ = -0.832H2O +2e- H↔ 2 + 2OH- Eθ = -0.83

OxidationEθ > more +ve easier to lose e4OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.232SO4

2- S↔ 2O82- + 2e Eθ = -2.01

О

H2 gasO2 gas

Ratio 1:2


OH-

OH-

SO42-

SO42-

H+

H+

H+

H+



Conc NaCI Electrolytic Cell

2H+ + 2e H↔ 2 Eθ = -0.832CI - CI↔ 2 + 2e Eθ = -1.36NaCI 2H→ 2 + CI2 + NaOH Eθ = -2.19


Na+ , CI- + H+ , OH- (from water)

+

+++++

-----





O2 + 4H+ +4e- ↔ H2O +1.23Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.331/2CI2 + e- ↔ CI- +1.36

1/2F2 + e- ↔ F- +2.87

Discharged CI- ion CI2 gas Discharged H+ ion to H2 gas

О

О

Na+/H+ CI-/OH-


Eθ =-ve → supply +2.19v to breakdown NaCI H→ 2 + CI2 + NaOH

Electrolysis (Concentrated Salt)


↓- Molten/aqueous




ОOxidation

Eθ > more +ve easier to lose e4OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.232CI- CI↔ 2 + 2e Eθ = -1.36

О

Ratio 1:2

H2 gas

CI2 gas

Dilute NaCI – OH- discharged due to Eθ valueConc NaCI – CI- discharged due to overpotential factorDischarged of H+ and OH- ion need addition voltage due to high activation energy for H2/O2 productionIf Conc CI- is high ↑ – it is preferred !!!!!!

OH-

OH-

CI -

CI -

H+

H+

Na+

Na+



Conc CuCI2 Electrolytic Cell

Cu2+ + 2e Cu↔ Eθ = +0.342CI- CI↔ 2 + 2e Eθ = -1.36CuCI2 Cu + O→ 2 Eθ = -0.89V



+

+++++

-----




2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.34

Cu+ + e- ↔ Cu +0.52I2 + 2e- ↔ 2I- +0.54Fe3+ + e- ↔ Fe2+ +0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23

1/2CI2 + e- ↔ CI- +1.36

1/2F2 + e- ↔ F- +2.87

Discharged CI- ion CI2 Discharged Cu2+ ion to Cu metal

О

Cu2+/H+ CI-/OH-

Eθ = -ve → supply +0.89 v to breakdown CuCI2 Cu→ + O2


↓- Molten/aqueous




OxidationEθ > more +ve easier to lose e4OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.232CI- CI↔ 2 + 2e Eθ = -1.36

ОО


Electrolysis (Concentrated Salt)

Dilute CuCI2 – OH- discharged due to Eθ valueConc CuCI2 – CI- discharged due to overpotential factorDischarged of H+ and OH- ion need addition voltage due to high activation energy for H2/O2 productionIf Conc CI- is high ↑ – it is preferred !!!!!!

CI2 gas

copper

OH -

OH -

CI -

CI -Cu2+

Cu2+

H+

H+

Carbon electrode

Discharge of ions 2 Cation 2 Anion


CuCI2 aqueous Electrolytic Cell



+

+++++

-----




2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.34

Cu+ + e- ↔ Cu +0.52I2 + 2e- ↔ 2I- +0.54Fe3+ + e- ↔ Fe2+ +0.77Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.331/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.511/2F2 + e- ↔ F- +2.87

Discharged Cu2+ ion to Cu metal

О

CI-/OH-



↓- Molten/aqueous




Copper electrode as anode

Cu easier discharge↓

due nature electrode↓

Cu → Cu2+ + 2e↓

Cu electrode dissolve

Copper electrode

OH- discharged↓

due to Eθ value↓

4OH- 2H↔ 2O+O2 + 4e↓

O2 gas

+++++

Cu → Cu2+ + 2e copperelectrode

Cu → 2e + Cu2+

Cu2+

Cu2+

Cu2+

Cu2+

Cu → 2e + Cu2+

Cu → 2e + Cu2+

Cu2+

Cu2+

e-e-

e e

e- e- e -

At AnodeCopper electrode oxidizes/dissolveConc copper ions unchangedMass of Cu anode decreasedMass of Cu cathode increased

Cu2+

Cu2+

Cu2+

OH-

OH-

CI -

CI -

H+

H+

Cu2+

Cu2+

Cu2+/H+

AgNO3 aqueous Electrolytic Cell

Carbon electrode

Discharge of ions 2 Anion

Oxidation ← Anode (+ve) ← Anion Cation → Cathode (-ve) → Reduction

Ag+ , NO3- + H+ , OH- (from water)

+

+++++

-----

NO3-/OH-



↓- Molten/aqueous



ReductionEθ > more +ve easier gain e2H+ + 2e H↔ 2 Eθ = -0.832H2O +2e- H↔ 2 + 2OH- Eθ = -0.83Ag+ + e Ag E↔ θ = +0.80

Copper electrode as anode

Ag easier discharge↓

due nature electrode↓

Ag → Ag+ + e↓

Ag electrode dissolve

Silver electrode

OH- discharged↓

due to Eθ value↓

4OH- 2H↔ 2O+O2 + 4e↓

O2 gas

+++++

Ag → Ag+ + e silverelectrode

Ag → e + Ag+

Ag+

Ag+

Ag+

Ag+

Ag → e + Ag+

Ag → e + Ag+

Ag+

Ag+

e-e-

e e

e- e- e -

At AnodeSilver electrode oxidizes/dissolveConc silver ions unchangedMass of Ag anode decreasedMass of Ag cathode increased

Ag+

Ag+

Ag+



2- + 4H+ + 2e- H↔ 2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40I2 + 2e- ↔ 2I- +0.54

Ag+ + e- ↔ Ag +0.801/2Br2 + e- ↔ Br- +1.07O2 + 4H+ +4e- ↔ H2O +1.23Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.331/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51S2 O8

2- + 2e ↔ SO42- +2.01

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F- +2.87

ОО

Discharged Ag+ ion to Ag

-----

OH -

OH -

NO3-

NO3-

Ag+

Ag+

H+

H+

Ag+/H+

Electrolyte Electrode Ions Cathode (-) Anode (+)

PbBr2 (molten) Carbon Pb2+/ Br- Pb2+ + 2e Pb →Pb

2Br- Br→ 2 + 2eBr2

CaCI2 (molten) Carbon Ca2+ /CI- Ca2+ +2e Ca→Ca

2CI- CI→ 2 + 2eCI2

NaCI Carbon Na+/ CI –

H+/OH-

2H+ + 2e H→ 2

H2

4OH- 2H↔ 2O +O2 + 4eO2

NaCI (conc)

Carbon Na+/ CI–

H+/OH-

2H+ + 2e H→ 2

H2

2CI- CI→ 2 + 2eCI2

NaI Carbon Na+/ I–

H+/OH-

2H+ + 2e H→ 2

H2

2I- I→ 2 + 2eI2

CuCI2 Carbon Cu2+/ CI–

H+/OH-

2H+ + 2e H→ 2

H2

4OH- 2H↔ 2O +O2 + 4eO2

CuCI2

(conc)Carbon Cu2+/CI-

H+/OH -

2H+ + 2e H→ 2

H2

2CI- CI→ 2 + 2eCI2

CuCI2 Copper Cu2+/CI- Cu2+ +2e Cu→Cu

Cu Cu→ 2+ + 2eCu

CuBr2 Carbon Cu2+ /Br-

H+/OH -

2H+ + 2e H→ 2

H2

2Br- Br→ 2 + 2eBr2

KI Carbon K+/I -

H+/OH -

2H+ + 2e H→ 2

H2

2I- I→ 2 + 2eI2

AgNO3 Carbon Ag+/NO3-

H+/OH -

Ag+ + e Ag→Ag

4OH- 2H↔ 2O +O2 + 4eO2

AgNO3 Silver Ag+/NO3- Ag+ + e Ag→ Ag Ag→ + + e

K2SO4 Carbon K+/SO42-

H+/OH -

2H+ + 2e H→ 2

H2

4OH- 2H↔ 2O +O2 + 4eO2

H2SO4 Carbon H+/SO42-

H+/OH -

2H+ + 2e H→ 2

H2

4OH- 2H↔ 2O +O2 + 4eO2

HCI Carbon H+/CI-

H+/OH -

2H+ + 2e H→ 2

H2

4OH- 2H↔ 2O +O2 + 4eO2

HCI (conc)

Carbon H+/CI-

H+/OH -

2H+ + 2e H→ 2

H2

2CI- CI→ 2 + 2eCI2

Ease Anion dischargedNO3

–

SO42-

CI–

Br–

I–

OH–

Ease Cation dischargedK+

Ca2+

Na+

Mg2+

Al 3+

Zn2+

Fe2+

Sn2+

Pb2+

H+

Cu2+

Ag+

easier

easier

Electrolytic cell


+ -



CathodeAnode


Relative E values of ion

Conc ion conc/diluted

Nature of electrode

PANIC

Positive is Anode, Negative Is Cathode

NO3– - diff to discharge

- ON for N is +5 (very high)- Diff to lose e to get higher

Current – measured in Amperes or Coulombs per second 1A = 1 Coulomb charge pass through a point in 1 second = 1C/s1 Coulomb charge (electron) = 6.28 x 10 18 electrons passing in 1 second

1 electron - carry charge of – 1.6 x 10 -19 C 6.28 x 10 18 electron - carry charge of - 1 C 1A6.02 x 10 23 electron (1 Mol) - carry charge of - 96500C 1F

Electric current

Flow electric charges (electron)From High electric potential – low potential

ond

electron

ond

CoulombA

sec.1

.1028.6

sec1

11

18×==

Current

Flow of charges

---

ItQ = t = Time/ s

Find amt charges pass through a sol if Current is 2.ooA, time is 15 mins

ItQ =

Q = Amt Charges/ CI = Current/ A

CQ 1800601500.2 =××=

Faraday’s constant (F) – charge on 1 mol of electron 96500 C mol-1

1

1923

965001

106.11002.6−

−

=×××=

×=

CmolF

CF

eLF

1A = 6.28 x 1018 e 1 second

L = Avogadro constant

1 Faraday – Quantity charge 96500C supply to 1 mol electron

Faraday's 1st Law Electrolysis Faraday's 2nd Law Electrolysis

Amt charges (Q)

Mass produce is directly proportional to the quantity of electricity/charges ( C )

Factor affecting mass substance liberated

Charge on ion

Current Time

ItQ =

Mass produce is inversely proportional to

charges on ion

Cu2+ + 2e Cu↔

Ag+ + e Ag↔

AI3+ + 3e AI↔

+1 +2 +3

1 mol e → 1 mol Ag 2 mol e → 1 mol Cu 3 mol e → 1 mol AI

Pass 1 mol e 1 mol e → 1 mol Ag 1 mol e → 1/2 mol Cu 1 mol e → 1/3 mol AI

Current – measured in Amperes or Coulombs per second 1A = 1 Coulomb charge pass through a point in 1 second = 1C/s1 Coulomb charge (electron) = 6.28 x 10 18 electrons passing in 1 second

1 electron - carry charge of – 1.6 x 10 -19 C 6.28 x 10 18 electron - carry charge of - 1 C 1A6.02 x 10 23 electron (1 Mol) - carry charge of - 96500C 1F

Electric current

Flow electric charges (electron)From High electric potential – low potential

ond

electron

ond

CoulombA

sec.1

.1028.6

sec1

11

18×==

Current

Flow of charges

---

ItQ = t = Time/ s

Find amt charges pass through a sol if Current is 2.ooA, time is 15 mins

ItQ =

Q = Amt Charges/ CI = Current/ A

CQ 1800601500.2 =××=

Faraday’s constant (F) – charge on 1 mol of electron 96500 C mol-1

1

1923

965001

106.11002.6−

−

=×××=

×=

CmolF

CF

eLF

1A = 6.28 x 1018 e 1 second

L = Avogadro constant

1 Faraday – Quantity charge 96500C supply to 1 mol electron

Copper (II) sulfate electrolyzed using current -- 0.150A for 5 hrs. Cal mass of Cu deposited

CQ

Q

ItQ

2700

60605150.0

=×××=

= Cu2+ + 2e Cu↔ 2 mol e → 1 mol Cu

0.028 mol e 0.014 mol Cu→emolC

emolC

...028.096500

27002700

...196500

=→

→

Find Current/I → Find Charge/Q → Find mol electron → Find Mass deposited

use Faraday’s constant

Mass = mol x RAMMass = 0.014 x 63.5Mass = 0.889 g

Mass deposited (Cathode)

Cu

11

Cu2+

Cu2+

Electrolysis

AIt

QI

ItQ

4.6605.12

4787

=×

==

=Cr3+ + 3e Cr↔ 1 mol Cr → 3 mol e

0.0165 mol Cr → 0.0495 mol e

Find Mass → Find mol electron → Find Charges/Q → Find current/I


Mass = mol x RAM0.86 = mol x 52.00 mol = 0.0165

Electrolysis Cr2(SO4)3 yield 0.86g of Cr after passing current for 12.5 min. Find amt of current used.

1 mol e → 96500C 0.0495 mol e 96500 x 0.0495→ = 4787 C

Find time /hrs need to produce 25g of Cr from Cr2(SO4)3 with current of 1.1A

Find Mass → Find mol electron → Find Charges/Q →Find current/I

Cr3+ + 3e Cr↔


1 mol Cr → 3 mol e 0.48 mol Cr → 1.44 mol e

Mass = mol x RAM 25 = mol x 52.00 mol = 0.48

1 mol e → 96500C 1.44 mol e 96500 x 1.44→ = 138960 C

1.351.1

138960

=

==

=

tI

Qt

ItQ


Cr3+

Cr3+

Cr

Find vol of H2 gas collect at cathode when aq sol Na2SO4 electrolyzed for 2.00 hours with a 10A.


Cr

Cr3+

Cr3+

Find Current/I → Find Charge/Q → Find mol electron → Find Vol

2H+ + 2e H↔ 2

CQ

Q

ItQ

72000

6060200.2

=×××=

=use Faraday’s constant

emolC

emolC

...746.096500

7200072000

...196500

=→

→ 2 mol e → 1 mol H2 0.746 mol e 0.373 mol H→ 2

H2 O2

22

33

44

Vol = 8.35 dm3


Amt charges (Q)



Charge on ion

Current Time

ItQ =

Mass produce is inversely proportional to charges on ion

Cu2+ + 2e Cu↔

Ag+ + e Ag↔

AI3+ + 3e AI↔

+1 +2 +3


Pass 1 mol electron across

1 mol e → 1 mol Ag 1 mol e → 1/2 mol Cu 1 mol e → 1/3 mol AI

Ag+

Ag+

--

--

--

++

++

++ Cu2+

Cu2+

AI3+

AI3+

AgNO3,CuSO4, AICI3 connect in series. Same amt current used.Cal mass Cu and Al when 10.8 g Ag deposited.

Ag+ + e Ag↔ 1 mol Ag → 1 mol e

0.1 mol Ag →0.1 mol e

Mass = mol x RAM10.8 = mol x 108 mol = 0.1

Cu2+ + 2e Cu↔ 2 mol e → 1 mol Cu

0.1 mol e → 0.05 mol Cu

AI3+ + 3e AI↔ 3 mol e → 1 mol AI

0.1 mol e → 0.03 mol AI

Mass Cu = 0.05 mol Mass AI = 0.03 mol

AgNO3, H3SO4 connect in series. Same amt current usedCal vol H2,O2 when 10.8 g Ag deposited.

--

Ag+

Ag+

O2H2

Ag+ + e Ag↔ 1 mol Ag → 1 mol e

0.1 mol Ag → 0.1 mol e

Mass = mol x RAM10.8 = mol x 108 mol = 0.1

2H+ + 2e H↔ 2 2 mol e → 1 mol H2

0.1 mol e 0.05 mol H→ 2

4OH- 2H↔ 2O +O2 + 4e 4 mol e → 1 mol O2 0.1 mol e 0.025 mol O→ 2

2.24 dm3

0.56 dm3


Amt charges (Q)



Charge on ion

Current Time

ItQ =


Cu2+ + 2e Cu↔

Ag+ + e Ag↔

AI3+ + 3e AI↔

+1 +2 +3



1 mol e → 1 mol Ag 1 mol e → 1/2 mol Cu 1 mol e → 1/3 mol AI

Purification of metal

Application of Electrolysis

Extraction reactive metal

Aluminium Sodium

- ve electrode

Aluminium metal

AI2O3

Al3+ + 3e → Al

Electroplating- Prevent corrosion- Improve appearance Copper, chromium, silver

- ve Sodium metal

Na+ + e → Na

NaCI + ve

----

----

++++

++++

++++

----

Anode (+ve)Plating metal

Cathode (-ve) Object

++

--

Anode (+ve)Impure Cu metal Mass decrease

Cathode (-ve) Pure Cu metal Mass increase

Cu2+ + 2e Cu↔

Cu2+

Cu2+

Cu2+

Cu Cu↔ 2+ + 2e

2CI- -2e → CI2

Electrolysis of KI

Electrolysis of waterExcellent Silver crystal formation

Galvanizing Iron with Zinc

PANIC

Positive is Anode, Negative Is Cathode


Relative E values of ion

Conc ion conc/diluted

Nature of electrode

Ease Cation dischargedK+

Ca2+

Na+

Mg2+

Al 3+

Zn2+

Fe2+

Sn2+

Pb2+

H+

Cu2+

Ag+ easier

Ease Anion dischargedNO3

–

SO42-

CI–

Br–

I–

OH–easier

NO3– - diff to discharge

- ON for N is +5 (very high)- Diff to lose e to get higher




Electrolytic cell

+ -

Faraday's 1st Law Electrolysis



Amt charges (Q)

Charge on ion

Current Time

ItQ =

Faraday's 2nd Law Electrolysis


+1 +2

Ag+ + e Ag↔

Cu2+ + 2e Cu↔ 1 mol e → 1 mol Ag 2 mol e → 1 mol Cu

1 mol e → 1 mol Ag 1 mol e → 1/2 mol Cu


Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/http://spmchemistry.onlinetuition.com.my/2013/10/electrolytic-cell.htmlhttp://www.chemguide.co.uk/physical/redoxeqia/introduction.htmlhttp://educationia.tk/reduction-potential-tablehttp://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s23-electrochemistry.html

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com

ib chemistry on electrolysis and faraday's law

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e cu e

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