ib chemistry on electrolysis and faraday's law
TRANSCRIPT
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
Conversion electrical to chemical energy
Electrochemistry
Conversion chemical to electrical energy
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
+
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+
Conversion electrical to chemical energy
Electrochemistry
Conversion chemical to electrical energy
Cathode (-ve) Reduction
Vs
Spontaneous rxn Non Spontaneous rxn
Anode (+ve) Oxidation
+
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
Find Eθcell (use reduction potential)
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
Find Eθcell (use reduction potential)
Pb2+ + 2e Pb E↔ θ = -0.132Br - Br↔ 2+ 2e Eθ = -1.07Pb2+ + 2Br - Pb→ +Br2 Eθ = -1.20V
Eθ = -1.20V-ve (NON spontaneous)
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 ↔
Compound broken down (LYSIS) energy needed
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+
Discharge of ions1 Cation + 1 Anion
Oxidation ← Anode (+ve) ← Anion
CaCI2 molten Electrolytic Cell
Find Eθcell (use reduction potential)
Ca2+ + 2e Ca E↔ θ = -2.872CI - CI↔ 2+ 2e Eθ = -1.36Ca2+ + 2CI - Ca→ +CI2 Eθ = -4.23V
Eθ = -4.23V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
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 ↔
Compound broken down (LYSIS) energy needed
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)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
Inert electrode Carbon/graphite
CI -
CI -
CI -
Ca2+
Ca2+
Ca2+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
NaCI aqueous Electrolytic Cell
2H+ + 2e H↔ 2 Eθ = -0.834OH - 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 2H→ 2 + O2 Eθ = -2.06V
Eθ = -2.06V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
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
- Nature of electrode
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
Inert electrode Carbon/graphite
OH-
OH-
CI -
CI -
H+
H+
Na+
Na+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
NaI aqueous Electrolytic Cell
2H+ + 2e H↔ 2 Eθ = -0.832I - I↔ 2 + 2e Eθ = -0.54NaI H→ 2 + I2 Eθ = -1.37V
Eθ = -1.37V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
Na+ , I- + 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- +0.40
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
- Nature of electrode
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 e2I- I↔ 2 + 2e Eθ = -0.544OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.23
О
Inert electrode Carbon/graphite
I -
I -
OH-
OH-H+
H+
Na+
Na+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
CuCI2 aqueous Electrolytic Cell
Cu2+ + 2e Cu↔ Eθ = +0.344OH- 2H↔ 2O + O2 + 4e Eθ = -1.23CuCI2 Cu + O→ 2 Eθ = -0.89V
Eθ = -0.89V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
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
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 +0.34
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)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
Inert electrode Carbon/graphite
OH-
OH-
CI -
CI -
H+
H+
Cu2+
Cu2+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
CuBr2 aqueous Electrolytic Cell
Cu2+ + 2e Cu↔ Eθ = +0.342Br- Br↔ 2 + 2e Eθ = -1.07CuBr2 Cu + Br→ 2 Eθ = -0.73V
Eθ = -0.73V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
Cu2+ , Br- + 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 +0.34
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
Electrolysis (Aqueous Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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 e2Br- Br↔ 2 + 2e Eθ = -1.074OH- 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 4H↔ + + O2 + 4e Eθ = -1.23
Inert electrode Carbon/graphite
Br-
Br-
OH-
OH-
Cu2+
Cu2+
H+
H+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
KI aqueous Electrolytic Cell
2H+ + 2e H↔ 2 Eθ = -0.832I- I↔ 2 + 2e Eθ = -0.54KI H→ 2+ Br2 Eθ = -1.37V
Eθ = -1.37V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
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
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- +0.40
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
Electrolysis (Aqueous Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
Inert electrode Carbon/graphite
OH-
OH-
I -
I -
H+
H+
K+
K+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
K2SO4 aqueous Electrolytic Cell
2H+ + 2e H↔ 2 Eθ = -0.834OH- 2H↔ 2O+ O2 + 4e Eθ = -1.23K2SO4
H→ 2+ O2 Eθ = -2.06V
Eθ = -2.06V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
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
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- +0.40I2 + 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
Electrolysis (Aqueous Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
Inert electrode Carbon/graphite
OH-
OH-
SO42-
SO42-
K+
K+
H+
H+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
AgNO3 aqueous Electrolytic Cell
Ag+ + e Ag E↔ θ = +0.804OH- 2H↔ 2O+ O2 + 4e Eθ = -1.23AgNO3
Ag + O→ 2 Eθ = -0.43V
Eθ = -0.43V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
Ag+ , NO3- + 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
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- +0.40I2 + 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
Electrolysis (Aqueous Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
Inert electrode Carbon/graphite
OH-
OH-
NO3-
NO3-
H+
H+
Ag+
Ag+
Discharge of ions1 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
H2SO4 aqueous Electrolytic Cell
2H+ + 2e H↔ 2 Eθ = -0.834OH - 2H↔ 2O + O2 + 4e Eθ = -1.232H2O 2H→ 2 + O2 Eθ = -2.06V
Eθ = -2.06V-ve (NON spontaneous)
Conversion electrical to chemical energy Energy needed to decompose compound!!!!!!!!
Cation → Cathode (-ve) → Reduction
H+ , SO42- + 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
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
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
Electrolysis (Aqueous Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
Inert electrode Carbon/graphite
OH-
OH-
SO42-
SO42-
H+
H+
H+
H+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
Conc NaCI Electrolytic Cell
2H+ + 2e H↔ 2 Eθ = -0.832CI - CI↔ 2 + 2e Eθ = -1.36NaCI 2H→ 2 + CI2 + NaOH Eθ = -2.19
Cation → Cathode (-ve) → Reduction
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 CI- ion CI2 gas Discharged H+ ion to H2 gas
О
О
Na+/H+ CI-/OH-
Inert electrode Carbon/graphite
Eθ =-ve → supply +2.19v to breakdown NaCI H→ 2 + CI2 + NaOH
Electrolysis (Concentrated Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
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+
Discharge of ions2 Cation + 2 Anion
Oxidation ← Anode (+ve) ← Anion
Conc CuCI2 Electrolytic Cell
Cu2+ + 2e Cu↔ Eθ = +0.342CI- CI↔ 2 + 2e Eθ = -1.36CuCI2 Cu + O→ 2 Eθ = -0.89V
Cation → Cathode (-ve) → Reduction
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↔ -2.71
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 +0.34
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
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
Inert electrode Carbon/graphite
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
Oxidation ← Anode (+ve) ← Anion
CuCI2 aqueous Electrolytic Cell
Cation → Cathode (-ve) → Reduction
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↔ -2.71
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 +0.34
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-
Electrolysis (Aqueous Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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
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-
Electrolysis (Aqueous Salt)
Factor affecting ion discharged (Selective Discharge)
↓- Molten/aqueous
- Relative E values of ion- Conc ion – conc/diluted
- Nature of electrode
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+
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
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- +0.40I2 + 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
Conversion electrical to chemical energy
+ -
Anode (+ve) Oxidation
Cathode (-ve) Reduction
CathodeAnode
Factor affecting ion discharged (Selective Discharge)
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
use Faraday’s constant
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↔
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
1.351.1
138960
=
==
=
tI
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 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
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 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
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 electron across
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
Factor affecting ion discharged (Selective Discharge)
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
Anode (+ve) Oxidation
Cathode (-ve) Reduction
Conversion electrical to chemical energy
Electrolytic cell
+ -
Faraday's 1st Law Electrolysis
Mass produce is directly proportional to the quantity of electricity/charges ( C )
Factor affecting mass substance liberated
Amt charges (Q)
Charge on ion
Current Time
ItQ =
Faraday's 2nd Law Electrolysis
Mass produce is inversely proportional to charges on ion
+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
Pass 1 mol electron across
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