Investigation of electrode material - redox couple systems ...
IB Chemistry on Electrochemical series, Redox Potential and Standard Electrode Potential
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Transcript of IB Chemistry on Electrochemical series, Redox Potential and Standard Electrode Potential
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