The chemical name for SHE is the Standard Hydrogen Electrode. It serves as the universally recognized reference electrode in electrochemistry, defining the zero point on the electrochemical potential scale.
Understanding the Standard Hydrogen Electrode (SHE)
The Standard Hydrogen Electrode (SHE) is a fundamental component in the study of electrochemistry. It is crucial for determining and comparing the reduction potentials of other half-cells. By convention, the standard electrode potential of the SHE is assigned a value of exactly 0 volts (V) at all temperatures.
Construction and Principles of SHE
The construction of a Standard Hydrogen Electrode involves specific conditions to ensure its standard reference potential:
- Platinum Electrode: A platinum electrode, typically coated with platinum black (a finely divided form of platinum), is used. Platinum is chosen because it is inert and provides a large surface area for the adsorption of hydrogen gas and the electron transfer reaction.
- Hydrogen Gas: Pure hydrogen gas at a standard pressure of 1 atmosphere (atm) or 1 bar is bubbled over the platinum electrode.
- Acid Solution: The electrode is immersed in an acid solution where the molarity of hydrogen ions (H⁺) is precisely 1 mole per cubic decimeter (1 M). This ensures a standard concentration of the reacting species.
- Hydroseal: To maintain the purity of the environment and prevent external contamination, particularly from atmospheric oxygen, a hydroseal is often incorporated into the SHE setup. This feature is vital for the accuracy and stability of the reference potential.
Table: Key Characteristics of SHE
| Characteristic | Description |
|---|---|
| Assigned Potential | 0.00 V (at all temperatures, by convention) |
| Components | Platinum electrode, 1 atm H₂(g), 1 M H⁺(aq) solution, hydroseal |
| Function | Reference point for measuring electrode potentials |
| Reaction | 2H⁺(aq) + 2e⁻ ⇌ H₂(g) |
| Application | Determining standard reduction potentials and calculating cell potentials |
Role in Electrochemistry
The SHE plays a pivotal role in electrochemistry by enabling the measurement of standard electrode potentials (E°) for various half-reactions. Since individual electrode potentials cannot be measured directly, they are always measured relative to a reference. The SHE provides this stable and reproducible reference point.
- Measuring Potentials: When another half-cell (e.g., a zinc electrode in zinc sulfate solution) is connected to the SHE, the measured potential difference across the galvanic cell directly corresponds to the standard potential of the other half-cell.
- Predicting Reactions: These measured standard potentials are then used to predict the spontaneity and direction of redox reactions and to calculate cell potentials for various electrochemical cells.
While the SHE is the theoretical standard, its practical implementation can be complex due to the need for precise control over gas pressure and ion concentration. For routine laboratory work, secondary reference electrodes like the Calomel Electrode or Silver/Silver Chloride Electrode are often used, as they are more convenient and stable, but their potentials are themselves calibrated against the SHE.
