What Are the Conditions and Uses of Standard Hydrogen Electrode?
Standard Hydrogen Electrode (SHE) is essential in chemistry and helps students understand redox reactions, electrochemical cells, and the measurement of electrode potentials. Mastering this topic simplifies solving problems and builds a strong foundation for advanced electrochemistry concepts.
What is Standard Hydrogen Electrode in Chemistry?
A Standard Hydrogen Electrode (SHE) refers to a primary reference electrode with a defined potential of zero volts. This means all standard electrode potentials for other electrodes are measured against SHE under specific standard conditions. This concept appears in chapters related to electrochemical cells, redox reactions, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The standard hydrogen electrode does not have a traditional molecular formula like a simple compound. It consists of an inert platinum electrode dipped in a 1M strong acid (like HCl) with hydrogen gas bubbling at 1 atm pressure. The platinum is coated with platinum black to increase the surface for the redox reaction. This setup forms a reference system in the class of gas-ion electrodes.
Preparation and Synthesis Methods
To prepare the standard hydrogen electrode in the laboratory:
- Take a clean platinum electrode and coat it with platinum black.
- Immerse the electrode into a beaker of 1M strong acid (like hydrochloric acid).
- Enclose it in a glass jacket to prevent air from entering.
- Pass pure, moist hydrogen gas over the platinum electrode at 1 atmosphere pressure.
- Maintain the temperature at 25°C (298K).
Physical Properties of Standard Hydrogen Electrode
The standard hydrogen electrode includes:
- Platinum wire and foil: inert, stable, and conductive.
- Hydrogen gas: colorless and odorless; supplied at 1 atm.
- Aqueous solution: transparent, usually 1M HCl providing 1M H+ ions.
- Typically maintained at 25°C for standard measurements.
Chemical Properties and Reactions
In the standard hydrogen electrode, the key equilibrium is:
H2 (g, 1 atm) → 2H+ (aq, 1M) + 2e-
This reaction is reversible. When SHE acts as an anode, hydrogen gas is oxidized. When as a cathode, hydrogen ions are reduced to hydrogen gas.
Frequent Related Errors
- Forgetting the standard conditions: 1M H+, 1 atm H2, 25°C.
- Not writing the electrode as Pt | H2(g,1 atm) | H+(aq,1M).
- Assuming platinum participates in the reaction rather than serving as a surface.
- Mixing up SHE and normal hydrogen electrode (NHE) terms.
Uses of Standard Hydrogen Electrode in Real Life
Standard hydrogen electrode is mainly used as a reference to measure the standard electrode potential of other electrodes. It helps in creating the electrochemical series, determining the feasibility of redox reactions, and standardizing measurements in physical chemistry and industrial processes.
Relation with Other Chemistry Concepts
The standard hydrogen electrode connects multiple chemistry topics. It is essential when understanding redox reactions, galvanic cells, and is required for calculations with the Nernst equation. SHE is also the baseline for measuring potentials in electrolysis and laboratory battery cells.
Step-by-Step Reaction Example
- Set up the SHE with platinum wire in 1M HCl and bubble H2 at 1 atm.
SHE (anode): H2(g,1atm) → 2H+(aq,1M) + 2e- - Connect to any other metal half-cell (e.g., copper or zinc with their salt solutions).
Write balanced cell equation depending on direction of electron flow. - Measure cell potential and compare with SHE standard (E0 = 0V for SHE).
Lab or Experimental Tips
Remember, SHE only gives accurate results when conditions are strictly controlled (1M H+, 1 atm H2, clean platinum). Vedantu educators suggest sketching the labelled SHE diagram in your notes for better recall and always mentioning the standard conditions in exam answers.
Try This Yourself
- Write the cell notation for an SHE connected to a copper half-cell.
- Explain why the platinum electrode must be coated with platinum black.
- State the standard conditions and why each is important for SHE.
Final Wrap-Up
We explored Standard Hydrogen Electrode (SHE)—its setup, cell notation, standard potential, and importance as the universal reference in electrochemistry. For more practice and detailed step-by-step lessons, visit Vedantu and discover topic-wise study material curated for every chemistry learner.
FAQs on Standard Hydrogen Electrode: Principle, Construction & Working
1. What is the Standard Hydrogen Electrode (SHE) and why is it important?
The Standard Hydrogen Electrode (SHE) is a universal reference electrode used to measure the standard electrode potentials of other electrodes in electrochemistry. It is important because:
- It has a defined potential of zero volts under standard conditions.
- It provides a reference point for comparing the reduction and oxidation potentials of other half-cells.
- It helps create the electrochemical series for various elements and compounds.
2. Why is the potential of the SHE assigned as zero volts?
The SHE potential is assigned zero volts by international convention because:
- Electrode potentials are always measured relative to some reference.
- Setting SHE at zero allows standardization and easy comparison with other electrodes.
- This assignment is arbitrary, but universally accepted for consistency in electrochemistry.
3. What are the main components and conditions for the Standard Hydrogen Electrode?
SHE consists of:
- A platinum electrode coated with platinum black.
- H2 gas at 1 atmosphere pressure.
- 1 M hydrogen ion (H+) concentration (usually from a strong acid).
- A temperature maintained at 25°C (298 K).
4. What is the standard hydrogen electrode equation and cell notation?
The half-cell reaction for the SHE is:
2H+ (aq, 1 M) + 2e− → H2(g, 1 atm)
Cell notation: Pt(s) | H2(g, 1 atm) | H+(aq, 1 M)
5. How is the SHE constructed and how does it work?
To construct the Standard Hydrogen Electrode (SHE):
- Place a platinum electrode in a solution containing 1 M H+ ions.
- Bubble pure hydrogen gas (H2) at 1 atm pressure over the electrode.
- The platinum surface speeds up the exchange of electrons between H+ and H2 gas.
- The electrode can act as either anode or cathode depending on the cell.
6. What are the main applications and limitations of the Standard Hydrogen Electrode?
Applications of SHE:
- Measuring the standard electrode potentials of other electrodes.
- Serving as a primary reference for electrochemical measurements.
Limitations:
- Hydrogen gas is flammable and requires safety precautions.
- Platinum surface can get contaminated, affecting accuracy.
- Setup is complex and not suitable for everyday laboratory use; secondary reference electrodes are often preferred.
7. Is the SHE always placed on the left side in cell representation?
The SHE is usually placed on the left side in the electrochemical cell notation when it acts as anode (oxidation), but its position depends on the reaction being studied. It can appear on either side based on whether it acts as an anode or cathode in the cell.
8. How does contamination of the platinum electrode affect the SHE?
Contamination of the platinum electrode reduces the effectiveness of the SHE by slowing down the hydrogen electrode reaction. This can lead to inaccurate potential measurements and unreliable results in electrochemical experiments.
9. How is the Standard Hydrogen Electrode replaced in modern laboratory setups?
The SHE is often replaced with secondary reference electrodes such as the calomel electrode or silver/silver chloride electrode. These alternatives are easier to handle, safer, and more convenient for regular laboratory use while maintaining reliable reference potential values.
10. What is the difference between Standard Hydrogen Electrode (SHE) and Normal Hydrogen Electrode (NHE)?
SHE and NHE are often used interchangeably, but technically, the SHE is maintained under exact standard conditions (1 M H+, 1 atm H2, 25°C), while the NHE may refer to a hydrogen electrode under approximate or slightly varied conditions in practical use.
11. Can the SHE be used to measure both oxidation and reduction potentials?
Yes, the SHE can act as both anode or cathode in electrochemical cells, so it is used to measure both oxidation and reduction potentials, depending on the direction of the reaction in the cell setup.
12. What are the safety concerns when handling hydrogen gas in the SHE setup?
Hydrogen gas is highly flammable and can form explosive mixtures with air. Proper ventilation, leak checks, and flame-proof equipment are essential to ensure safety when using hydrogen gas in SHE apparatus.
