When measuring half-cell potentials, the reference electrode commonly used is the standard hydrogen electrode (SHE). This electrode is assigned a half-cell potential of zero volts and serves as the universal reference point for determining the potentials of other electrodes.
4 Key Points Explained: Which Electrode is Used as a Reference for Measuring Half-Cell Potentials?
1. Definition and Role of Reference Electrodes
Reference electrodes are essential components in electrochemical cells. They provide a stable and well-known electrode potential. They are used to measure the potential of the working electrode by maintaining a constant potential, allowing for accurate measurements of half-cell reactions.
2. Standard Hydrogen Electrode (SHE)
The SHE is composed of a platinum electrode immersed in a solution with hydrogen ions at unit activity, with hydrogen gas adsorbed on the platinum. It is assigned an arbitrary half-cell potential of zero volts (E0 = 0.000 V), making it the standard reference for all other electrode potentials. The half-cell reaction for the SHE is:
[ 2H^+(aq) + 2e^- \rightleftharpoons H_2(g) ]
3. Practical Limitations of SHE
The practical application of the SHE is limited due to the challenges in maintaining unit activity for hydrogen ions and hydrogen gas. These limitations make the SHE less convenient for routine use in laboratories, leading to the adoption of alternative reference electrodes.
4. Alternative Reference Electrodes
Saturated Calomel Electrode (SCE)
The SCE is a commonly used secondary reference electrode, known for its stability and ease of use. It consists of mercury in contact with a saturated solution of potassium chloride and mercurous chloride (calomel).
Silver-Silver Chloride Electrode (Ag/AgCl)
This electrode is another popular choice due to its simplicity and stability. It involves a silver wire coated with silver chloride and immersed in a chloride ion solution.
Importance of Reference Electrodes in Electrochemical Measurements
Reference electrodes ensure that the potential of the working electrode can be accurately measured and compared across different experiments. They play a crucial role in the calculation of cell potentials, which are essential for understanding and predicting the behavior of electrochemical systems.
Calculation of Cell Potentials
The cell potential is determined by the difference in electrode potentials between the working electrode and the reference electrode. Accurate measurement of these potentials allows for the prediction of the overall chemical reaction in the cell and the quantification of the voltage generated.
In summary, while the SHE is the theoretical standard for measuring half-cell potentials, practical considerations often lead to the use of secondary reference electrodes like the SCE and Ag/AgCl in laboratory settings. These electrodes provide stable and reproducible potentials, ensuring accurate and reliable electrochemical measurements.
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