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Standard Electrode Potential

 
1.2 Standard Electrode Potential
 
Definition of Electrode Potential

Potential difference produced when an equilibrium is established between metal M and the aqueous solution containing metal \(M^{n+}\)ions in a half-cell.
 
The Electrode Potential of A Cell
  • Electrode potential cannot be measured directly.
  • The value is determined based on the difference of electrode potential between two half-cells.
  • The electrode potential can be measured by pairing up the electrode to the standard reference electrode system.
  • The international consensus is the standard hydrogen electrode.
 
The image contains a blue rectangular box with rounded corners. Inside the box, there is a list of standard conditions for the standard electrode potential measurement. The conditions listed are: - The concentration of ions in an aqueous solution is 1 mol dm⁻³. - The gas pressure of 1 atm or 101 kPa. - The temperature at 25°C or 298K. - Platinum is used as an inert electrode when a half-cell is not a metal electrode. There is also a hand holding a pen, writing the title at the top of the box. The bottom right corner has the logo ‘Pandai.’ The background has red and blue geometric shapes on the sides.
 
Standard Hydrogen Electrode 

The image shows a diagram of an electrochemical cell. The cell contains a solution with 1.0 mol dm⁻³ of hydrogen ions. A platinum electrode coated with platinum (IV) oxide is immersed in the solution. Hydrogen gas at 1 atm is supplied to the cell through a platinum wire. The setup is likely used for a standard hydrogen electrode.

  • Function of platinum(IV) oxide, \(PtO_2\): To increase the surface area of platinum, Pt to adsorb hydrogen gas, \(H_2\).
  • This is done so that hydrogen molecules are in closer contact with hydrogen ions, \(H^+\) in the solution.
  • Half equation of the hydrogen half-cell;
    • \(2H^+ (aq) +2e^- \rightleftharpoons H_2(g)\)
  • The standard hydrogen electrode potential, Eº is given the value of 0.00 V:
    • \(H^+ (aq) +e^- \rightleftharpoons \frac{1}{2}H_2(g) \hspace{1cm}E^0=0.00V\)
 
Standard Electrode Potential Value, Eº
  • Apparatus set-up to determine standard electrode potential, Eº of zinc is as below:

The image depicts an electrochemical cell setup. On the left side, there is a beaker containing a zinc electrode (Zn) immersed in a solution with a concentration of 1.0 mol dm⁻³ of zinc ions (Zn²⁺). On the right side, there is a beaker with a platinum electrode (Pt) immersed in a solution with a concentration of 1.0 mol dm⁻³ of hydrogen ions (H⁺), and hydrogen gas (H₂) at 1 atm is being bubbled through the solution. A salt bridge connects the two solutions. The cell potential is indicated as 0.76 V.

  • Since the standard hydrogen potential is 0.00 V, the voltmeter reading of 0.76 V shows the electrode potential of zinc.
  • Zinc, Zn has a greater tendency to release electrons compared to hydrogen.
  • Hence, zinc, Zn becomes the negative terminal.
  • Electrons move from zinc electrode, Zn (negative terminal) to platinum electrode, Pt (positive terminal) through the connecting wires.
 
Electrode Zinc Hydrogen
Terminal Negative Positive
Half equation \(Zn(p) \rightarrow Zn^{2+} (aq) +2e^-\) \(2H^{+} (aq) +2e^-\rightarrow H_2(g)\)
Reaction Oxidation Reduction
Standard electrode potential for half cell

\(Zn^{2+} (aq) +2e^- \rightleftharpoons Zn(s)\\ \,\\ E^0=-0.76V\)

The negative symbol shows that zinc electrode is the negative terminal when connected to the standard hydrogen electrode

  
 
Oxidising Agents and Reducing Agents Based on The Value of Standard Electrode Potential
  • The standard electrode potential, Eº is also known as the standard reduction potential.
  • All half-cell equations are written as reduction.
  • Eº value is a measure of the tendency of a substance to accept or donate electrons.
    • \(\text{Oxidising agent }+ \text{electron} \rightleftharpoons \text{Reducing agent}\)
Standard Electrode Potential Series

This image is a table of half-cell equations with their corresponding standard electrode potentials (E°) at 298 K. The table is divided into two sections by a horizontal line. The left column lists the half-cell reactions, while the right column shows their E° values in volts (V). The top of the table has a pink highlight around the Mg²⁺/Mg half-cell equation with an E° of -2.38 V. The bottom of the table has a blue highlight around the Ag⁺/Ag half-cell equation with an E° of +0.80 V. An arrow on the left indicates increasing strength as oxidizing agents, and an arrow on the right indicates increasing strength as reducing agents.
Comparison of standard electrode potential, Eº value
  • Is used to determine whether silver, Ag or magnesium, Mg is an oxidising agent or reducing agent.
When Eº Value of Ag is More Positive When Eº Value of Ag is More Negative

Silver ion, 𝐴𝑔+ on the left side is a stronger oxidising agent.

Magnesium atom, Mg on the right side is a stronger reducing agent.

It is easier for 𝐴𝑔+ ion to receive electrons and undergo reduction.

It is easier for magnesium atom, Mg to release electrons and undergo oxidation.

Conversely, silver atom, Ag on the right side is difficult to release electrons.

Conversely, magnesium ion, 𝑀𝑔2+Mg2+ on the left side is difficult to accept electrons.

 
The Relationship between Eº value to The Strength of a Substance as an Oxidizing Agent and a Reducing Agent

 

Molecules or Ions with a More Positive or Less Negative Standard Electrode Potential Value Eº Atoms or Ions with a More Negative or Less Positive Standard Electrode Potential Value Eº
Has a greater tendency to accept electrons. Has a greater tendency to release electrons.
Easier to undergo reduction reaction. Easier to undergo oxidation reaction.
A stronger oxidising agent. A stronger reducing agent.
 

 

 

 

 


 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of pandai.

Standard Electrode Potential

 
1.2 Standard Electrode Potential
 
Definition of Electrode Potential

Potential difference produced when an equilibrium is established between metal M and the aqueous solution containing metal \(M^{n+}\)ions in a half-cell.
 
The Electrode Potential of A Cell
  • Electrode potential cannot be measured directly.
  • The value is determined based on the difference of electrode potential between two half-cells.
  • The electrode potential can be measured by pairing up the electrode to the standard reference electrode system.
  • The international consensus is the standard hydrogen electrode.
 
The image contains a blue rectangular box with rounded corners. Inside the box, there is a list of standard conditions for the standard electrode potential measurement. The conditions listed are: - The concentration of ions in an aqueous solution is 1 mol dm⁻³. - The gas pressure of 1 atm or 101 kPa. - The temperature at 25°C or 298K. - Platinum is used as an inert electrode when a half-cell is not a metal electrode. There is also a hand holding a pen, writing the title at the top of the box. The bottom right corner has the logo ‘Pandai.’ The background has red and blue geometric shapes on the sides.
 
Standard Hydrogen Electrode 

The image shows a diagram of an electrochemical cell. The cell contains a solution with 1.0 mol dm⁻³ of hydrogen ions. A platinum electrode coated with platinum (IV) oxide is immersed in the solution. Hydrogen gas at 1 atm is supplied to the cell through a platinum wire. The setup is likely used for a standard hydrogen electrode.

  • Function of platinum(IV) oxide, \(PtO_2\): To increase the surface area of platinum, Pt to adsorb hydrogen gas, \(H_2\).
  • This is done so that hydrogen molecules are in closer contact with hydrogen ions, \(H^+\) in the solution.
  • Half equation of the hydrogen half-cell;
    • \(2H^+ (aq) +2e^- \rightleftharpoons H_2(g)\)
  • The standard hydrogen electrode potential, Eº is given the value of 0.00 V:
    • \(H^+ (aq) +e^- \rightleftharpoons \frac{1}{2}H_2(g) \hspace{1cm}E^0=0.00V\)
 
Standard Electrode Potential Value, Eº
  • Apparatus set-up to determine standard electrode potential, Eº of zinc is as below:

The image depicts an electrochemical cell setup. On the left side, there is a beaker containing a zinc electrode (Zn) immersed in a solution with a concentration of 1.0 mol dm⁻³ of zinc ions (Zn²⁺). On the right side, there is a beaker with a platinum electrode (Pt) immersed in a solution with a concentration of 1.0 mol dm⁻³ of hydrogen ions (H⁺), and hydrogen gas (H₂) at 1 atm is being bubbled through the solution. A salt bridge connects the two solutions. The cell potential is indicated as 0.76 V.

  • Since the standard hydrogen potential is 0.00 V, the voltmeter reading of 0.76 V shows the electrode potential of zinc.
  • Zinc, Zn has a greater tendency to release electrons compared to hydrogen.
  • Hence, zinc, Zn becomes the negative terminal.
  • Electrons move from zinc electrode, Zn (negative terminal) to platinum electrode, Pt (positive terminal) through the connecting wires.
 
Electrode Zinc Hydrogen
Terminal Negative Positive
Half equation \(Zn(p) \rightarrow Zn^{2+} (aq) +2e^-\) \(2H^{+} (aq) +2e^-\rightarrow H_2(g)\)
Reaction Oxidation Reduction
Standard electrode potential for half cell

\(Zn^{2+} (aq) +2e^- \rightleftharpoons Zn(s)\\ \,\\ E^0=-0.76V\)

The negative symbol shows that zinc electrode is the negative terminal when connected to the standard hydrogen electrode

  
 
Oxidising Agents and Reducing Agents Based on The Value of Standard Electrode Potential
  • The standard electrode potential, Eº is also known as the standard reduction potential.
  • All half-cell equations are written as reduction.
  • Eº value is a measure of the tendency of a substance to accept or donate electrons.
    • \(\text{Oxidising agent }+ \text{electron} \rightleftharpoons \text{Reducing agent}\)
Standard Electrode Potential Series

This image is a table of half-cell equations with their corresponding standard electrode potentials (E°) at 298 K. The table is divided into two sections by a horizontal line. The left column lists the half-cell reactions, while the right column shows their E° values in volts (V). The top of the table has a pink highlight around the Mg²⁺/Mg half-cell equation with an E° of -2.38 V. The bottom of the table has a blue highlight around the Ag⁺/Ag half-cell equation with an E° of +0.80 V. An arrow on the left indicates increasing strength as oxidizing agents, and an arrow on the right indicates increasing strength as reducing agents.
Comparison of standard electrode potential, Eº value
  • Is used to determine whether silver, Ag or magnesium, Mg is an oxidising agent or reducing agent.
When Eº Value of Ag is More Positive When Eº Value of Ag is More Negative

Silver ion, 𝐴𝑔+ on the left side is a stronger oxidising agent.

Magnesium atom, Mg on the right side is a stronger reducing agent.

It is easier for 𝐴𝑔+ ion to receive electrons and undergo reduction.

It is easier for magnesium atom, Mg to release electrons and undergo oxidation.

Conversely, silver atom, Ag on the right side is difficult to release electrons.

Conversely, magnesium ion, 𝑀𝑔2+Mg2+ on the left side is difficult to accept electrons.

 
The Relationship between Eº value to The Strength of a Substance as an Oxidizing Agent and a Reducing Agent

 

Molecules or Ions with a More Positive or Less Negative Standard Electrode Potential Value Eº Atoms or Ions with a More Negative or Less Positive Standard Electrode Potential Value Eº
Has a greater tendency to accept electrons. Has a greater tendency to release electrons.
Easier to undergo reduction reaction. Easier to undergo oxidation reaction.
A stronger oxidising agent. A stronger reducing agent.
 

 

 

 

 


 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of pandai.
Chapter : Redox Equilibrium
Topic : Standard Electrode Potential
Form 5 Chemistry
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