ib chemistry on electrochemical series, redox potential and standard electrode potential
DESCRIPTION
IB Chemistry on Electrochemical Series, Redox Potential, Standard Electrode Potential, Oxidizing and Reducing Agent.TRANSCRIPT
STRONG Reducing Agent
WEAK Reducing Agent
WEAK Oxidising Agent
STRONG Oxidising Agent
• Species on TOP left • Low ↓ tendency to gain e • Li+ + e → Li • Eθ Li= - 3.04V • WEAK oxidising Agent • Reduction NOT favourable
• Species on TOP right • High ↑tendency to lose e • Li → Li + + e • Eθ Li = +3.04V • STRONG reducing Agent •Oxidation favourable
• Species on BOTTOM left • High ↑ tendency to gain e • F2 + 2e → 2F-
• Eθ F2= +2.87V • STRONG oxidising Agent •Reduction favourable
• Species on BOTTOM right • Low ↓tendency to lose e • F - →1/2F2 + e • Eθ F2 = -2.87V • WEAK reducing Agent •Oxidation NOT favourable
Electrochemical Series • Shows the ease/tendency of species to accept/lose electrons
• Written as standard reduction potential
Voltaic Cell for Zn/Cu electrode
Copper reduction Half Cell Zinc oxidation Half Cell
Eθcell = Eθ
(+ve) - Eθ (-ve)
Eθcell = Eθ
(cathode) (red) - Eθ (anode)(oxi)
Eθcell = Eθ
(Cu) - Eθ (Zn)
= 0.34 – (-0.76)
= +1.10V
Zn2+ + 2e → Zn Eθcell = -0.76V (Reduction potential)
Cu2+ + 2e → Cu Eθcell = +0.34V (Reduction potential)
Zn → Zn 2+ + 2e Eθ(Zn) (Oxidation potential)
Cu 2+ + 2e → Cu Eθ (Cu) (Reduction potential)
Zn + Cu 2+ → Cu + Zn 2+ Eθcell + 1.10V
Cell Diagram for Zn/Cu half cells
Electrode/electrolyte ║ Electrolyte/electrode
(-ve)/oxidation ║ (+ve)/reduction
Zn/Zn2+ ║ Cu 2+/Cu
Determine Eθcell using std electrode potential and formula Eθ
cell = Eθ (+ve) - E
θ (-ve)
Voltaic Cell for Mg/Fe electrode
Iron reduction Half Cell
Eθcell = Eθ
(+ve) - Eθ (-ve)
Eθcell = Eθ
(cathode) (red) - Eθ (anode) (oxi)
Eθcell = Eθ
(Fe) - Eθ (Mg)
= 0.44 – (-2.36)
= +1.92V
Mg2+ + 2e → Mg Eθcell = -2.36V (Reduction potential)
Fe2+ + 2e → Fe Eθcell = +0.44V (Reduction potential)
Mg → Mg 2+ + 2e Eθ(Mg) (Oxidation potential)
Fe 2+ + 2e → Fe Eθ (Fe) (Reduction potential)
Mg + Fe2+ → Fe + Mg2+ Eθcell = + 1.92V
Cell Diagram for Mg/Fe half cells
Electrode/electrolyte ║ Electrolyte/electrode
(-ve)/oxidation ║ (+ve)/reduction
Mg/Mg2+ ║ Fe2+/Fe
Determine Eθcell using std electrode potential and formula Eθ
cell = Eθ (+ve) - E
θ (-ve)
Magnesium oxidation Half Cell
STRONG Reducing Agent
WEAK Reducing Agent
WEAK Oxidising Agent
STRONG Oxidising Agent
• Species on TOP left • Low ↓ tendency to gain e • Li+ + e → Li • Eθ Li= - 3.04V • WEAK oxidising Agent • Reduction NOT favourable
• Species on TOP right • High ↑tendency to lose e • Li → Li + + e • Eθ Li = +3.04V • STRONG reducing Agent •Oxidation favourable
• Species on BOTTOM left • High ↑ tendency to gain e • F2 + 2e → 2F-
• Eθ F2= +2.87V • STRONG oxidising Agent •Reduction favourable
• Species on BOTTOM right • Low ↓tendency to lose e • F - →1/2F2 + e • Eθ F2 = -2.87V • WEAK reducing Agent •Oxidation NOT favourable
Electrochemical Series • Shows the ease/tendency of species to accept/lose electrons
• Written as standard reduction potential
Steps to follow 1. Species on top right / Eθ = (-ve) are Strong Reducing Agent (RA)
2. Species on bottom left/ Eθ = (+ve) are Strong Oxidising Agent (OA)
3. For a redox reaction to happen, choose
• One (OA) from left
• One (RA) from right
4. Arrange the redox couple in order of their Eθ values
• Eθ = (-ve) on top
• Eθ = (+ve) at bottom
5. Follow the anticlockwise rule or Z rule
Reaction between Zn + Cu2+ is possible (spontaneous)
Zn is strong RA on the right
• Undergo oxidation Zn → Zn2+ + 2e
Cu 2+ is strong OA on the left
• Undergo reduction Cu2+ +2e → Cu
• Z rule is followed and EθCell is (+ve)
•Zn + Cu2+ → Zn2+ +Cu
Using Standard Electrode Potential to compare the strength of Oxidising/Reducing agents
Is reaction between Zn + Cu2+ possible (spontaneous) ?
Eθ Cell calculation
Zn → Zn 2+ + 2e Eθ(Zn) = +0.76V (Oxidation potential)
Cu 2+ + 2e → Cu Eθ (Cu) = +.34V (Reduction potential)
Zn + Cu 2+ → Cu + Zn 2+ Eθcell = + 1.10V
SPONTANEOUS
Using Standard Electrode Potential to predict if reaction between Zn + Cu2+ is possible
Reaction between Zn + Cu2+ is spontaneous
Zn is strong RA on the right
• Undergo oxidation Zn → Zn2+ + 2e
Cu 2+ is strong OA on the left
• Undergo reduction Cu2+ +2e → Cu
• Z rule is followed and EθCell is (+ve)
• Zn + Cu2+ → Zn2+ + Cu
Is reaction between Zn + Cu2+ possible (spontaneous) ?
Zn → Zn 2+ + 2e Eθ(Zn) = +0.76V (Oxidation potential)
Cu 2+ + 2e → Cu Eθ (Cu) = +.34V (Reduction potential)
Zn + Cu 2+ → Cu + Zn 2+ Eθcell = + 1.10V
EθCell calculation
Using Standard Electrode Potential to predict if reaction between Mg + Cu2+ is possible
Reaction between Mg + Cu2+ is spontaneous
Mg is strong RA on the right
• Undergo oxidation Mg → Mg2+ + 2e
Cu2+ is strong OA on the left
• Undergo reduction Cu2+ +2e → Cu
• Z rule is followed and EθCell is (+ve)
• Mg + Cu2+ → Mg2+ + Cu
Eθ Cell calculation
Mg → Mg2+ + 2e Eθ(Mg) = +2.37V (Oxidation potential)
Cu 2+ + 2e → Cu Eθ (Cu) = +0.34V (Reduction potential)
Mg + Cu2+ → Cu + Mg2+ Eθcell = + 2.71V
Is reaction between Mg + Cu2+ possible (spontaneous) ?
SPONTANEOUS
SPONTANEOUS
Using Standard Electrode Potential to predict if reaction between Ag + Zn2+ is possible
Reaction between Ag + Zn2+ is NOT spontaneous
Ag is weak RA on the right
• Undergo oxidation Ag → Ag+ + e
Zn2+ is weak OA on the left
• Undergo reduction Zn2+ + 2e → Zn
• Z rule is NOT X followed and Eθ Cell is (-ve)
• Ag + Zn2+ → Zn2+ +Cu Х
Is reaction between Ag + Zn2+ possible (spontaneous) ?
Ag → Ag+ + e Eθ(Ag) = -0.80V (Oxidation potential)
Zn2+ + 2e → Zn Eθ (Zn) = -0.76V (Reduction potential)
Ag + Zn2+ → Zn + Ag+ Eθcell = -1.56V
Eθ Cell calculation
Using Standard Electrode Potential to predict if reaction between Fe3+ + CI - is possible
Reaction between Fe3+ + CI - is NOT spontaneous
CI - is weak RA on the right
• Undergo oxidation 2CI - → CI2 + 2e
Fe3+ is weak OA on the left
• Undergo reduction Fe3+ +e → Fe2+
• Z rule is NOT X followed and Eθ Cell is (-ve)
• Fe3+ + 2CI - → Fe2+ +CI2 Х
Eθ Cell calculation
2CI - → CI2 + 2e Eθ(CI) = -1.36V (Oxidation potential)
Fe3+ + e → Fe2+ Eθ (Fe) = +0.77V (Reduction potential)
2CI - + Fe3+ → CI2 + Fe2+ Eθcell = -0.59V
Is reaction between Fe3+ + CI - possible (spontaneous) ?
NON
SPONTANEOUS
NON
SPONTANEOUS
Using Standard Electrode Potential to predict if reaction between AI + H+ is possible
Reaction between AI + H+ (HCI) is spontaneous
AI is strong RA on the right
• Undergo oxidation AI → AI3+ + 3e
H+ is strong OA on the left
• Undergo reduction 2H+ + 2e → H2
• Z rule is followed and EθCell is (+ve)
• AI + 2H+ → Al3+ + H2
Is reaction between AI + H+ possible (spontaneous) ?
AI → AI3+ + 3e Eθ(AI) = +1.66V (Oxidation potential)
2H+ + 2e → H2 Eθ (H2) = 0.00V (Reduction potential)
AI + 2H+ → AI3+ + H2 Eθ
cell = +1.66V
Eθ Cell calculation
Using Standard Electrode Potential to predict if reaction between Cu + H + is possible
Reaction between Cu + H + (HCI) is NOT spontaneous
Cu is weak RA on the right
• Undergo oxidation Cu → Cu2+ + 2e
H+ is weak OA on the left
• Undergo reduction 2H+ + 2e → H2
• Z rule is NOT X followed and EθCell is (-ve)
• Cu + 2H + → Cu2+ +H2 Х
Eθ Cell calculation
Cu → Cu2+ + 2e Eθ(Cu) = -0.34V (Oxidation potential)
2H+ + 2e → H2 Eθ (H2) = +0.00V (Reduction potential)
Cu + 2H+ → H2 + Cu2+ Eθcell = -0.34V
Is reaction between Cu + H+ possible (spontaneous) ?
NON
SPONTANEOUS
SPONTANEOUS
Using Standard Electrode Potential to predict reaction between halogens and halides
Will Chlorine oxidise bromide to bromine ? (Cl2 + Br - → CI - + Br2)
Will Bromine oxidise iodide to iodine ? (Br2 + I - → Br - + I2 )
Will Iodine oxidise chloride to chlorine ? (I2 + CI - → I - + CI2)
Steps to follow
1. Arrange standard electrode potential in order shown below (Highest Eθ = +ve at bottom)
2. Pick one (OA) and one (RA) from both sides and follow Z rule
Reaction between Cl2 + 2I - → CI - + I2 is spontaneous
I - is strong RA on the right
• Undergo oxidation 2I - → I2 + 2e
CI2 is strong OA on the left
• Undergo reduction CI2 + 2e → 2CI -
• Z rule is followed and EθCell is (+ve)
• Cl2 + 2I - → CI - + I2
Is reaction between CI2 + I - possible (spontaneous) ?
2I - → I2 + 2e Eθ(I2) = -0.54V (Oxidation potential)
CI2 + 2e → 2CI - Eθ (CI2) = +1.33V (Reduction potential)
Cl2 + 2I - → CI -+ I2 Eθcell = +0.79V
Eθ Cell calculation
Highest Eθ (+ve) at the bottom
SPONTANEOUS
Using Standard Electrode Potential to predict if reaction between CI2 + I - is possible
Reaction between Cl2 + 2I - → CI - + I2 is spontaneous
I - is strong RA on the right
• Undergo oxidation 2I - → I2 + 2e
CI2 is strong OA on the left
• Undergo reduction CI2 + 2e → 2CI -
• Z rule is followed and EθCell is (+ve)
• Cl2 + 2I - → CI - + I2
Is reaction between CI2 + I - possible (spontaneous) ?
2I - → I2 + 2e Eθ(I2) = -0.54V (Oxidation potential)
CI2 + 2e → 2CI - Eθ (CI2) = +1.33V (Reduction potential)
Cl2 + 2I - → CI -+ I2 Eθcell = +0.79V
Using Standard Electrode Potential to predict if reaction between Br2 + I - is possible
Reaction between Br2 + 2I - → 2Br - + I2 is spontaneous
I - is strong RA on the right
• Undergo oxidation 2I - → I2 + 2e
Br2 is strong OA on the left
• Undergo reduction Br2 + 2e → 2Br -
• Z rule is followed and Eθ Cell s (+ve)
• Br2 + 2I - → 2Br - + I2
2I - → I2 + 2e Eθ(I2) = -0.54V (Oxidation potential)
Br2 + 2e → 2Br - Eθ(Br2) = +1.07V (Reduction potential)
Br2 + 2I - → 2Br - + I2 Eθcell = +0.53V
Is reaction between Br2 + I - possible (spontaneous) ?
Eθ Cell calculation
Eθ Cell calculation
SPONTANEOUS
SPONTANEOUS
Using Standard Electrode Potential to predict if reaction between I2 + CI - possible
Reaction between I2 + 2CI - → 2I - + CI2 NOT spontaneous
CI - is weak RA on the right
• Undergo oxidation 2CI - →CI2 + 2e
I2 is weak OA on the left
• Undergo reduction I2 + 2e → 2I -
• Z rule is NOT X followed and Eθ Cell is (-ve)
• I2 + 2CI - → 2I - + CI2
Is reaction between I2 + CI - possible (spontaneous) ?
2CI - → CI2 + 2e Eθ(CI2) = -1.33V (Oxidation potential)
I2 + 2e → 2I - Eθ (I2) = +0.54V (Reduction potential)
I2 + 2CI - → 2I - + CI2 Eθcell = -0.79V
Using Standard Electrode Potential to predict if reaction between I2 + CI2 possible
Reaction between I2 + CI2 is NOT spontaneous
• CANNOT have TWO species on the same side
• Z rule is NOT X followed and Eθ Cell is (-ve)
Is reaction between I2 + CI2 possible (spontaneous) ?
Eθ Cell calculation
NON
SPONTANEOUS
NON
SPONTANEOUS
Calculate the Eθ or emf for the following cells
Reaction between Mg + Sn2+ is spontaneous
Mg is strong RA on the right
• Undergo oxidation Mg → Mg2+ + 2e
Sn2+ is strong OA on the left
• Undergo reduction Sn2+ + 2e → Sn
• Z rule is followed and Eθ Cell is (+ve)
• Mg + Sn2+ → Mg2+ + Sn
Reaction between Mg + Sn2+
Fe 2+ → Fe3+ + e Eθ(Fe) = -0.777V (Oxidation potential)
MnO4 - + 8H+ + 5e → Mn2+ + 4H2O Eθ
(Mn) = +1.51V (Reduction potential)
2MnO4 -+ 5Fe2+ + 8H+ → 5Fe3+ + Mn2++4H2O Eθ
cell = +0.75V
Eθ Cell calculation
Mg/Mg2+ ║ Sn2+/Sn
Reaction between Fe2+ + MnO4 -
Reaction between Fe2+ + CI - is spontaneous
Fe 2+ is strong RA on the right
• Undergo oxidation Fe2+ → Fe3+ + e
MnO4 - is strong OA on the left
• Undergo reduction MnO4 - + 8H+ + 5e → Mn2+ + 4H2O
• Z rule is followed and Eθ Cell is (+ve)
• 2MnO4 - + 5Fe2+ + 8H+ → 5Fe3+ + Mn2+ + 4H2O
Mg → Mg2+ + 2e Eθ(Mg) = +2.37V (Oxidation potential)
Sn 2+ + 2e → Sn Eθ(Sn) = -0.14V (Reduction potential)
Mg + Sn2+ → Mg2+ + Sn Eθcell = + 2.23V
Eθ Cell calculation
Fe2+/Fe3+ ║ MnO4 -/Mn2+
SPONTANEOUS
SPONTANEOUS
Is the reaction between Ag + AI3+ → Ag+ + AI possible ?
Reaction between Ag + AI3+ is NOT spontaneous
Ag is weak RA on the right
• Undergo oxidation Ag → Ag+ + e
Al3+ is weak OA on the left
• Undergo reduction AI3+ + 3e → Al
• Z rule is NOT X followed and EθCell is (-ve)
• Ag + AI3+ → Ag+ + AI
Reaction between Ag + Al3+
Eθ Cell calculation
Ag → Ag+ + e Eθ(Ag) = -0.80V (Oxidation potential)
AI3+ + 3e → AI Eθ(AI) = -1.66V (Reduction potential)
Ag + AI3+ → Ag+ + AI Eθcell = -2.46V
NON
SPONTANEOUS