The standard hydrogen electrode (SHE) is a cornerstone in the realm of electrochemistry. Acting as a universal reference point, it facilitates the measurement and comparison of electrode potentials, ensuring consistency and standardisation across various experiments and studies.
Construction and Use of the Standard Hydrogen Electrode
Components and Assembly
- Platinum Wire and Plate: A platinum wire, connected to a platinum plate, is submerged into an acidic solution. Platinum's inert nature ensures it doesn't interfere with the reactions, serving merely as a conduit for electron flow.
- Hydrogen Gas: Hydrogen gas, maintained at a pressure of 1 atm, is continuously bubbled through the acidic solution. This action ensures a consistent concentration of hydrogen ions in the solution, providing a stable environment for reactions.
- Acidic Solution: A 1M solution of a strong acid, typically hydrochloric acid (HCl), is used. This solution offers a rich source of hydrogen ions (H+), essential for the half-reaction at the electrode.
Functioning and Role
When connected to another electrode in an electrochemical cell, the SHE plays a pivotal role:
1. Oxidation of Hydrogen: At the platinum surface, hydrogen gas undergoes oxidation, releasing electrons: H2(g) → 2H+(aq) + 2e-. This reaction is fundamental to the SHE's operation. Understanding the balance of redox reactions is crucial in this context, and further explanation can be found on balancing redox reactions.
2. Electron Flow: The electrons released from the oxidation of hydrogen travel through the external circuit, producing an electric current. This flow is what's measured to determine the potential difference between the SHE and the connected electrode.
3. Reference Point: Given its consistent behaviour and defined potential of 0 volts, the SHE serves as a universal reference, allowing for the measurement of other electrode potentials. This is particularly important when exploring galvanic cells and electrolytic cells, where the SHE provides a baseline for potential difference.
Measuring Electrode Potentials
Procedure
1. Setup: The SHE is meticulously connected to the electrode whose potential is under scrutiny. A salt bridge, facilitating ion movement, and an external circuit, allowing for electron flow, link the two electrodes. Understanding the role of the SHE in voltaic cells can provide deeper insights into its setup and function.
2. Measurement: A voltmeter, a precise instrument, measures the potential difference between the SHE and the test electrode. This measurement is crucial for determining the electrode's potential.
3. Determination: Since the SHE's potential is a defined 0 volts, the measured potential difference directly equates to the electrode potential of the test electrode. This direct correlation simplifies the process, eliminating the need for complex calculations. For those studying pH and its calculations, the SHE's role in determining electrode potentials is similarly foundational, as detailed on calculating pH.
Significance
The SHE's role in measuring electrode potentials cannot be overstated. By providing a consistent and universally accepted reference, it ensures that measurements are standardised across different laboratories and studies. This standardisation is vital for the scientific community, ensuring that results are comparable and universally understood.
Importance in Establishing the Electrochemical Series
Definition
The electrochemical series, a vital tool in electrochemistry, is an ordered list of elements based on their standard electrode potentials. This series offers invaluable insights into elemental reactivity and the potential direction of redox reactions.
Role of SHE
- Benchmarking: The SHE's potential, set at 0 volts, serves as the foundational benchmark against which all other electrode potentials are gauged and compared.
- Predictive Power: The electrochemical series, with its ordered list of elements, allows scientists to predict the direction of redox reactions. Elements positioned higher in the series have a natural tendency to lose electrons (undergo oxidation) to elements situated lower in the series.
- Reactivity Insights: Beyond predictions, the series offers insights into elemental reactivity. Metals with more negative electrode potentials are typically more reactive than those with positive potentials. This information is invaluable for industries and researchers working with metals and their compounds.
- Applications in Industry: The electrochemical series, underpinned by measurements using the SHE, has practical applications. It aids in the selection of metals for specific industrial applications, especially where corrosion resistance is crucial.
FAQ
The potential of the standard hydrogen electrode (SHE) is defined, rather than measured, to be 0 volts. This definition was established to provide a consistent and universal reference point in electrochemistry. By setting the SHE's potential at 0 volts, it allows for the direct measurement of other electrode potentials against this standard. When another electrode is connected to the SHE in an electrochemical cell, the potential difference measured is essentially the potential of the test electrode, simplifying comparisons and ensuring standardisation across various studies.
Yes, the SHE can be used to measure the electrode potentials of alkaline or basic solutions. However, it's important to note that while the SHE itself contains an acidic solution, the electrode potential it measures is a property of the test electrode and is independent of the pH of the SHE. When measuring the potential of an electrode in a basic solution, the SHE and the test electrode are connected via a salt bridge, which allows ion movement without mixing the two solutions. This setup ensures accurate measurements regardless of the pH of the test solution.
Maintaining a pressure of 1 atm for the hydrogen gas in the SHE is crucial for standardisation. The electrode potential of any half-cell can be influenced by the concentration of the involved species, and in the case of gases, this concentration is directly related to pressure. By keeping the hydrogen gas pressure at a consistent 1 atm, it ensures that the SHE's behaviour remains consistent across different experiments and setups. This consistency is vital for ensuring that electrode potential measurements using the SHE are comparable and universally accepted.
If the hydrogen gas pressure in the SHE deviates from the standard 1 atm, it could lead to a change in the electrode potential of the SHE. According to the Nernst equation, electrode potential is influenced by the concentration (or in the case of gases, the partial pressure) of the reacting species. A deviation from the standard pressure would mean that the SHE is no longer operating under standard conditions. This could lead to inconsistencies in measurements and comparisons, making it crucial to maintain the hydrogen gas pressure at 1 atm to ensure the reliability and standardisation of the SHE in electrochemical studies.
Platinum is chosen for the construction of the standard hydrogen electrode (SHE) due to its unique properties. Firstly, platinum is chemically inert, meaning it doesn't react with the acidic solution or hydrogen gas, ensuring that it doesn't interfere with the reactions taking place. Secondly, platinum has excellent conductivity, facilitating efficient electron transfer. Lastly, its surface readily adsorbs hydrogen gas, promoting the oxidation half-reaction essential for the SHE's operation. These combined properties make platinum the ideal choice, ensuring consistent and reliable measurements in electrochemistry.
Practice Questions
The standard hydrogen electrode (SHE) holds paramount importance in electrochemistry as it serves as a universal reference point for measuring and comparing electrode potentials. Its consistent behaviour and defined potential of 0 volts ensure that measurements across different experiments and studies are standardised. The basic construction of the SHE involves a platinum wire connected to a platinum plate submerged in an acidic solution, typically a 1M solution of hydrochloric acid (HCl). Hydrogen gas, maintained at a pressure of 1 atm, is continuously bubbled through this solution, ensuring a consistent concentration of hydrogen ions, which are essential for the half-reaction at the electrode.
The standard hydrogen electrode (SHE), with its potential set at 0 volts, acts as the foundational benchmark against which all other electrode potentials are gauged and compared. This consistent and universally accepted reference allows for the creation of the electrochemical series, an ordered list of elements based on their standard electrode potentials. The significance of the electrochemical series lies in its predictive power. By referring to this series, scientists can predict the direction of redox reactions. Elements positioned higher in the series tend to lose electrons (undergo oxidation) to elements situated lower in the series. This ordered arrangement offers invaluable insights into elemental reactivity and potential redox reactions, making it a vital tool in electrochemistry.
