Question

Explain the standard electrode potential of an electrode. How is it measured?

Short answer

Answer: The standard electrode potential is a measure of the tendency of a half-cell (or electrode) to either gain or lose electrons when in contact with a solution of its own ions at a specific temperature. It is used to predict the direction of electron flow and the spontaneity of redox reactions. It is measured by setting up an electrochemical cell by connecting the electrode to a standard hydrogen electrode and measuring the cell potential using a voltmeter. The standard electrode potential can then be calculated using the Nernst equation, where under standard conditions, the cell potential equals the standard electrode potential of the electrode.

Step-by-step solution

Define the Standard Electrode Potential

The standard electrode potential is a measure of the tendency of a half-cell (or electrode) to either gain or lose electrons when it is in contact with a solution of its own ions at a specific temperature. It is also the potential difference between the half-cell and the standard hydrogen electrode, which is assigned a potential of 0.00 volts (V) at all temperatures.

Significance of Standard Electrode Potential

The standard electrode potential plays a crucial role in redox reactions, serving as a tool to predict the direction of electron flow and the spontaneity of a reaction. A higher standard electrode potential means a higher tendency for the electrode to accept electrons from the other half-cell, acting as the oxidizing agent. Conversely, a lower standard electrode potential indicates a higher tendency for the electrode to give away electrons to the other half-cell, acting as the reducing agent.

The Nernst Equation

The Nernst equation is used to determine the electrode potential of an electrode depending on the concentrations of the ions involved in the redox reaction. The equation is given by: E = E° - (RT / nF) × lnQ Where: - E is the electrode potential - E° is the standard electrode potential - R is the gas constant (8.314 J/mol K) - T is the temperature in Kelvin - n is the number of electrons transferred in the redox reaction - F is the Faraday's constant (96,485 C/mol) - Q is the reaction quotient

Measuring the Standard Electrode Potential

To measure the standard electrode potential of an electrode, it is necessary to set up an electrochemical cell by connecting the electrode to a standard hydrogen electrode. The following steps describe the process: 1. Set up the standard hydrogen electrode: The standard hydrogen electrode is composed of a platinum wire, covered with platinum black, immersed in an aqueous solution containing a 1M concentration of hydrogen ions (H⁺) and connected to a volt meter. A stream of hydrogen gas is bubbled through the solution at a pressure of 1 atm and a temperature of 298 K (25°C). 2. Connect the electrode of interest: The electrode whose standard electrode potential is to be measured is connected to the standard hydrogen electrode through a salt bridge or a porous disk. 3. Measure the cell potential: The cell potential, or the potential difference between the two electrodes, is measured using the voltmeter. The potential difference should be positive for the reaction to be spontaneous. 4. Calculate the standard electrode potential: The standard electrode potential of the electrode can now be calculated using the Nernst equation: E = E° - (RT / nF) × lnQ Assuming the reaction conditions to be standard (1M solution and 298 K temperature), the Nernst equation simplifies to E = E°. Since the standard hydrogen electrode potential is 0.00 V, the cell potential equals the standard electrode potential of the electrode: E° = cell potential Now, you have successfully explained the standard electrode potential and its measurement method.

Key concepts

Electrochemical Cell

An electrochemical cell is a device that converts chemical energy into electrical energy through a spontaneous redox reaction. It consists of two half-cells, each with its own electrode and electrolyte. When these half-cells are connected by a conductive wire and a salt bridge, electrons flow from the anode (where oxidation occurs) to the cathode (where reduction takes place). This flow of electrons through the external circuit is what we harness as electricity.

The power of an electrochemical cell is determined by its electrode potentials, which can be measured against a standard such as the standard hydrogen electrode. Understanding how these cells work is essential for various practical applications, from batteries to corrosion prevention.

Nernst Equation

The Nernst equation is a fundamental formula used in electrochemistry to calculate the actual electrode potential as it changes with conditions such as concentration and temperature. The equation is given by:
\( E = E^° - (RT / nF) \times \ln Q \), where:\( E \) is the electrode potential, \( E^° \) is the standard electrode potential, \( R \) is the gas constant, \( T \) is the temperature in Kelvin, \( n \) is the number of electrons transferred, \( F \) is the Faraday's constant, and \( Q \) is the reaction quotient.

Acknowledging the Nernst equation's role is crucial for students who are exploring electrochemistry, as it provides a bridge between theory and actual experimental conditions. By using this equation, disparities in temperature, pressure, and concentration are accounted for in electrochemical reactions.

Redox Reactions

Redox reactions form the core of electrochemical cells. They involve the transfer of electrons between chemical species, with reduction (gain of electrons) occurring at one electrode and oxidation (loss of electrons) at another.

Accurately comprehending redox processes is essential for working with electrochemistry. They are described by half-reactions, each with an electrode potential. When combined, these potentials can predict the cell potential and the reaction's spontaneity. High standard electrode potentials mean the substance is more likely to be reduced and act as the oxidizing agent, while lower potentials suggest it is more likely to oxidize and behave as the reducing agent.

Standard Hydrogen Electrode

The standard hydrogen electrode (SHE) is the absolute reference used to measure the electrode potentials of other electrodes. It's considered the 'zero point' of the electrochemical scale. The SHE is a platinum wire coated with platinum black, immersed in an acidic solution where hydrogen gas at one atmosphere bubbles around it.

This role of the standard hydrogen electrode in measuring standard electrode potentials cannot be overstated. By comparing an unknown electrode potential to that of the SHE, you can establish a scale to predict the direction of electron flow and understand the behavior of the electrodes in redox reactions.