IB Chemistry on Electrolysis and Faraday's Law

Types voltaic cell

Conversion electrical energy to chemical energy

Electrochemistry

Electrolytic cell Voltaic cell

NH4CI and ZnCI2

Chemical and electrical energy

Redox rxn (Oxidation/reduction)

Movement electron Produce electricity

Conversion chemical energy to electrical energy

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

Chemical rxn

Electric current

Daniell cell Alkaline cell Dry cell Nickel cadmium cell

Primary cell (Non rechargeable)

MnO2 and KOH

Secondary cell (Rechargeable)

Conversion electrical to chemical energy

Electrochemistry

Electrolytic cell Voltaic 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

О

О О - -

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

+

О

О -

Zn → Zn 2+ + 2e (oxidized)

Cu2+ + 2e → Cu (reduced)

Zn2+

Zn2+

Zn2+

Zn2+

-

- - - → + +

+

Cu2+

Cu2+

Cu2+

-e -e +

+ +

- - -

2Br-→ Br2 + 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



+

О

О -

-e 1.10 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 Eθ = -0.76V Cu2+ + 2e ↔ Cu Eθ = +0.34V

Cu half cell (+ve) Reduction

Zn half cell (-ve) Oxidation

Zn + Cu2+ → Zn2+ + Cu Eθ = ?????

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

Eθ = +1.10V +ve (spontaneous)

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


2Br - ↔ Br2+ 2e Eθ = -1.07 Pb2+ + 2e ↔ Pb Eθ = -0.13 Pb2+ + 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 ions 1 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 Eθ = -0.13 2Br - ↔ Br2+ 2e Eθ = -1.07 Pb2+ + 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/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 + 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 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 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

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

2Br - ↔ Br2+ 2e Pb2+ + 2e ↔ Pb


О

О

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 Eθ = -2.87 2CI - ↔ CI2+ 2e Eθ = -1.36 Ca2+ + 2CI - → Ca +CI2 Eθ = -4.23V




Liquid – Ca2+ and CI- ions

+

+

+

+

+

+

-

-

-

-

-


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 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 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

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

2CI - ↔ CI2+ 2e Ca2+ + 2e ↔ Ca


О

О

Ca2+ CI -

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

Electrolysis (Molten Salt)






CI -

CI -

CI -

Ca2+

Ca2+

Ca2+



NaCI aqueous Electrolytic Cell

2H+ + 2e ↔ H2 Eθ = -0.83

4OH - ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O → 2H2 + O2 Eθ = -2.06V




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

+

+

+

+

+

+

-

-

-

-

-


Li+ + e- ↔ Li -3.04 K+ + e- ↔ K -2.93 Ca2+ + 2e- ↔ Ca -2.87 Na+ + e- ↔ Na -2.71 Al3+ + 3e- ↔ AI -1.66 Mn2+ + 2e- ↔ Mn -1.19 2H2O +2e- ↔ H2 + 2OH- -0.83 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 O2 + 4H+ +4e- ↔ H2O +1.23 Cr2O7

2-+14H+ +6e- ↔ 2Cr3+ +1.33 1/2CI2 + 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 → H2 + O2

Electrolysis (Aqueous Salt)





Reduction Eθ > more +ve easier gain e Na+ + e ↔ Na Eθ = -2.71 2H+ + 2e ↔ H2 E

θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83

О

Oxidation Eθ > more +ve easier to lose e 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23 2CI- ↔ CI2 + 2e E

θ = -1.36

О


OH-

OH-

CI -

CI -

H+

H+

Na+

Na+



NaI aqueous Electrolytic Cell

2H+ + 2e ↔ H2 Eθ = -0.83

2I - ↔ I2 + 2e Eθ = -0.54 NaI → H2 + I2 Eθ = -1.37V




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

+

+

+

+

+

+

-

-

-

-

-



2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 I2 + 2e- ↔ 2I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 O2 + 4H+ +4e- ↔ H2O +1.23 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + 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 → H2 + I2







θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83

О

Oxidation Eθ > more +ve easier to lose e 2I- ↔ I2 + 2e E

θ = -0.54 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23

О


I -

I -

OH-

OH- H+

H+

Na+

Na+



CuCI2 aqueous Electrolytic Cell

Cu2+ + 2e ↔ Cu Eθ = +0.34

4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 CuCI2 → Cu + O2 Eθ = -0.89V




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

+

+

+

+

+

+

-

-

-

-

-


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 2H2O +2e- ↔ H2 + 2OH- -0.83 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 Cu+ + e- ↔ Cu +0.52 I2 + 2e- ↔ 2I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 O2 + 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






Reduction Eθ > more +ve easier gain e 2H+ + 2e ↔ H2 E

θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83 Cu2+ + 2e ↔ Cu Eθ = +0.34 О

Oxidation

Eθ > more +ve easier to lose e 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23 2CI- ↔ CI2 + 2e E

θ = -1.36

О О


OH-

OH-

CI -

CI -

H+

H+

Cu2+

Cu2+



CuBr2 aqueous Electrolytic Cell

Cu2+ + 2e ↔ Cu Eθ = +0.34

2Br- ↔ Br2 + 2e Eθ = -1.07 CuBr2 → Cu + Br2 Eθ = -0.73V




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

+

+

+

+

+

+

-

-

-

-

-



2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 Cu+ + e- ↔ Cu +0.52 I2 + 2e- ↔ 2I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 1/2Br2 + e- ↔ Br- +1.07 O2 + 4H+ +4e- ↔ H2O +1.23 1/2CI2 + e- ↔ CI- +1.36 MnO4

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








Oxidation

Eθ > more +ve easier to lose e 2Br- ↔ Br2 + 2e E



Br-

Br-

OH-

OH-

Cu2+

Cu2+

H+

H+



KI aqueous Electrolytic Cell

2H+ + 2e ↔ H2 Eθ = -0.83

2I- ↔ I2 + 2e Eθ = -0.54 KI → H2+ Br2 Eθ = -1.37V




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

+

+

+

+

+

+

-

-

-

-

-


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


- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 1/2F2 + 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→ H2 + I2






Reduction Eθ > more +ve easier gain e K+ + e ↔ K Eθ = -2.93 2H+ + 2e ↔ H2 E

θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83

О

Oxidation Eθ > more +ve easier to lose e 2I- ↔ I2 + 2e E


О О


OH-

OH-

I -

I -

H+

H+

K+

K+



K2SO4 aqueous Electrolytic Cell

2H+ + 2e ↔ H2 Eθ = -0.83

4OH- ↔ 2H2O+ O2 + 4e Eθ = -1.23 K2SO4

→ H2+ O2 Eθ = -2.06V




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

+

+

+

+

+

+

-

-

-

-

-


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


- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 S2 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→ H2 + O2






Reduction Eθ > more +ve easier gain e K+ + e ↔ K Eθ = -2.93 2H+ + 2e ↔ H2 E

θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83

О

Oxidation Eθ > more +ve easier to lose e 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23 2SO4

2- ↔ S2O82- + 2e E

θ = -2.01

О О

H2 gas

Ratio 1:2

O2 gas


OH-

OH-

SO42-

SO42-

K+

K+

H+

H+



AgNO3 aqueous Electrolytic Cell

Ag+ + e ↔ Ag Eθ = +0.80 4OH- ↔ 2H2O+ O2 + 4e Eθ = -1.23 AgNO3

→ Ag + O2 Eθ = -0.43V




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

+

+

+

+

+

+

-

-

-

-

-



2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 1/2O2 + H2O +2e- ↔ 2OH- +0.40 I2 + 2e- ↔ 2I- +0.54 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 O2 + 4H+ +4e- ↔ H2O +1.23 1/2CI2 + e- ↔ CI- +1.36 MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51 S2 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 + O2







θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83 Ag+ + e ↔ Ag Eθ = +0.80

О

Oxidation Eθ > more +ve easier to lose e 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23 NO3

- cannot be discharged


OH-

OH-

NO3-

NO3-

H+

H+

Ag+

Ag+



H2SO4 aqueous Electrolytic Cell

2H+ + 2e ↔ H2 Eθ = -0.83

4OH - ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O → 2H2 + O2 Eθ = -2.06V




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

+

+

+

+

+

+

-

-

-

-

-




2-+14H+ +6e- ↔ 2Cr3+ +1.33 1/2CI2 + e- ↔ CI- +1.36 S2 O8

2- + 2e ↔ SO42- +2.01

1/2F2 + 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 → H2 + O2







θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83

Oxidation Eθ > more +ve easier to lose e 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23 2SO4

2- ↔ S2O82- + 2e E

θ = -2.01

О

H2 gas O2 gas

Ratio 1:2


OH-

OH-

SO42-

SO42-

H+

H+

H+

H+



Conc NaCI Electrolytic Cell

2H+ + 2e ↔ H2 Eθ = -0.83

2CI - ↔ CI2 + 2e Eθ = -1.36 NaCI → 2H2 + CI2 + NaOH Eθ = -2.19


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

+

+

+

+

+

+

-

-

-

-

-




2-+14H+ +6e- ↔ 2Cr3+ +1.33 1/2CI2 + 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 → H2 + CI2 + NaOH

Electrolysis (Concentrated Salt)






θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83

О

Oxidation Eθ > more +ve easier to lose e 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23 2CI- ↔ CI2 + 2e E

θ = -1.36

О

Ratio 1:2

H2 gas

CI2 gas

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

OH-

OH-

CI -

CI -

H+

H+

Na+

Na+



Conc CuCI2 Electrolytic Cell

Cu2+ + 2e ↔ Cu Eθ = +0.34

2CI- ↔ CI2 + 2e Eθ = -1.36 CuCI2 → Cu + O2 Eθ = -0.89V



+

+

+

+

+

+

-

-

-

-

-



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







Oxidation

Eθ > more +ve easier to lose e 4OH- ↔ 2H2O + O2 + 4e Eθ = -1.23 2H2O ↔ 4H+ + O2 + 4e Eθ = -1.23 2CI- ↔ CI2 + 2e E

θ = -1.36

О О


Electrolysis (Concentrated Salt)

Dilute CuCI2 – OH- discharged due to Eθ value Conc CuCI2 – CI- discharged due to overpotential factor Discharged of H+ and OH- ion need addition voltage due to high activation energy for H2/O2 production If 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- ↔ H2SO3 + H2O +0.17 Cu2+ + 2e- ↔ Cu +0.34 Cu+ + e- ↔ Cu +0.52 I2 + 2e- ↔ 2I- +0.54 Fe3+ + e- ↔ Fe2+ +0.77 Ag+ + e- ↔ Ag +0.80 1/2Br2 + e- ↔ Br- +1.07 O2 + 4H+ +4e- ↔ H2O +1.23 Cr2O7

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

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

Discharged Cu2+ ion to Cu metal

О

CI-/OH-








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- ↔ 2H2O+O2 + 4e ↓

O2 gas

+

+

+

+

+

Cu → Cu2+ + 2e copper

electrode

Cu → 2e + Cu2+

Cu2+

Cu2+

Cu2+

Cu2+

Cu → 2e + Cu2+

Cu → 2e + Cu2+ Cu2+

Cu2+

e-

e- e e

e- e- e -

At Anode Copper electrode oxidizes/dissolve Conc copper ions unchanged Mass of Cu anode decreased Mass 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-







θ = -0.83 2H2O +2e- ↔ H2 + 2OH- Eθ = -0.83 Ag+ + e ↔ Ag Eθ = +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- ↔ 2H2O+O2 + 4e ↓

O2 gas

+

+

+

+

+

Ag → Ag+ + e silver

electrode

Ag → e + Ag+

Ag+

Ag+

Ag+

Ag+

Ag → e + Ag+

Ag → e + Ag+ Ag+

Ag+

e-

e- e e

e- e- e -

At Anode Silver electrode oxidizes/dissolve Conc silver ions unchanged Mass of Ag anode decreased Mass of Ag cathode increased

Ag+

Ag+

Ag+



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

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

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

2- + 2e ↔ SO42- +2.01

MnO4- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

1/2F2 + e- ↔ F- +2.87

О

О

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- → Br2 + 2e Br2

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

2CI- → CI2 + 2e CI2

NaCI Carbon Na+/ CI –

H+/OH-

2H+ + 2e → H2

H2

4OH- ↔ 2H2O +O2 + 4e O2

NaCI (conc)

Carbon Na+/ CI–

H+/OH-

2H+ + 2e → H2

H2

2CI- → CI2 + 2e CI2

NaI Carbon Na+/ I–

H+/OH-

2H+ + 2e → H2

H2

2I- → I2 + 2e I2

CuCI2 Carbon Cu2+/ CI–

H+/OH-

2H+ + 2e → H2

H2

4OH- ↔ 2H2O +O2 + 4e O2

CuCI2

(conc) Carbon

Cu2+/CI-

H+/OH - 2H+ + 2e → H2

H2

2CI- → CI2 + 2e CI2

CuCI2 Copper

Cu2+/CI-

Cu2+ +2e → Cu

Cu Cu → Cu2+ + 2e

Cu

CuBr2 Carbon Cu2+ /Br-

H+/OH -

2H+ + 2e → H2

H2

2Br- → Br2 + 2e Br2

KI Carbon K+/I -

H+/OH -

2H+ + 2e → H2

H2

2I- → I2 + 2e I2

AgNO3 Carbon Ag+/NO3-

H+/OH -

Ag+ + e → Ag Ag

4OH- ↔ 2H2O +O2 + 4e O2

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

K2SO4 Carbon K+/SO42-

H+/OH -

2H+ + 2e → H2

H2

4OH- ↔ 2H2O +O2 + 4e O2

H2SO4 Carbon H+/SO42-

H+/OH -

2H+ + 2e → H2

H2

4OH- ↔ 2H2O +O2 + 4e O2

HCI Carbon H+/CI-

H+/OH -

2H+ + 2e → H2

H2

4OH- ↔ 2H2O +O2 + 4e O2

HCI (conc)

Carbon H+/CI- H+/OH -

2H+ + 2e → H2

H2

2CI- → CI2 + 2e CI2

Ease Anion discharged NO3

–

SO42-

CI–

Br–

I–

OH–

Ease Cation discharged K+

Ca2+

Na+

Mg2+

Al 3+

Zn2+

Fe2+

Sn2+

Pb2+

H+

Cu2+

Ag+

easier

easier

Electrolytic cell


+ -



Cathode Anode


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/s 1 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 1A 6.02 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/ C

I = 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/s 1 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 1A 6.02 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/ C

I = 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 RAM Mass = 0.014 x 63.5 Mass = 0.889 g

Mass deposited

(Cathode)

Cu

1

Cu2+

Cu2+

Electrolysis

AI

t

QI

ItQ

4.6

605.12

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 RAM 0.86 = 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 use Faraday’s constant

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

1.35

1.1

138960

t

I

Qt

ItQ

Mass deposited

(Cathode)

Cr3+

Cr3+

Cr

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

Mass deposited

(Cathode)

Cr

Cr3+

Cr3+

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

2H+ + 2e ↔ H2

CQ

Q

ItQ

72000

6060200.2


emolC

emolC

...746.096500

7200072000

...196500

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

H2 O2

2

3

4

Vol = 8.35 dm3


Amt charges (Q)



Charge on ion

Current Time

ItQ



+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 RAM 10.8 = 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 used Cal vol H2,O2 when 10.8 g Ag deposited.

-

- Ag+

Ag+

O2 H2

Ag+ + e ↔ Ag

1 mol Ag → 1 mol e 0.1 mol Ag → 0.1 mol e

Mass = mol x RAM 10.8 = mol x 108 mol = 0.1

2H+ + 2e ↔ H2

2 mol e → 1 mol H2 0.1 mol e → 0.05 mol H2

4OH- ↔ 2H2O +O2 + 4e

4 mol e → 1 mol O2 0.1 mol e → 0.025 mol O2

2.24 dm3

0.56 dm3


Amt charges (Q)



Charge on ion

Current Time

ItQ



+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 ↔ Cu2+ + 2e

2CI- -2e → CI2

Electrolysis of KI

Electrolysis of water Excellent 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 discharged K+

Ca2+

Na+

Mg2+

Al 3+

Zn2+

Fe2+

Sn2+

Pb2+

H+

Cu2+

Ag+ easier

Ease Anion discharged NO3

–

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


http://www.youtube.com/watch?v=LGwPfo_eunY&feature=plcp&context=C40db210VDvjVQa1PpcFP8zrwoEIYAiOf7SHO8tOGe5tpKjc0MUZ0=

http://www.youtube.com/watch?v=EE58a5fN468&feature=related

http://www.youtube.com/watch?v=fnyBldC4Ra4&context=C4676e77ADvjVQa1PpcFOZ9pl6Z0TBrNjCCByUH-33WMjBUPq2N30=

http://www.youtube.com/watch?v=jimPImGKPy8&feature=plcp&context=C4530cfeVDvjVQa1PpcFOZ9pl6Z0TBrA2CHKf1MgG-LXV5ekv2Oug=

Education

IB Chemistry on Electrolysis and Faraday's Law