What NEET Asks
- Questions on calculating standard electrode potentials using SHE as a reference.
- Conceptual understanding of SHE's definition, construction, and its role in the electrochemical series.
- Problems involving the Nernst equation where SHE is one of the half-cells under non-standard conditions.
Key Points
- The Standard Hydrogen Electrode (SHE) is the primary reference electrode, assigned an arbitrary standard electrode potential of exactly 0.00 V.
- Standard conditions for SHE are: 1 M H solution, 1 atm H gas pressure, and 298 K (25°C).
- It consists of a platinum electrode (inert) immersed in an acidic solution, with hydrogen gas bubbled over it.
- SHE can act as both an anode (oxidation: H → 2H + 2e) or a cathode (reduction: 2H + 2e → H), depending on the other half-cell.
- It enables the determination of unknown standard electrode potentials of other electrodes by forming a galvanic cell.
Must-Know Formula / Reaction
- SHE Half-Reaction (Reduction): 2H(aq, 1 M) + 2e → H(g, 1 atm); E° = 0.00 V
- SHE Half-Reaction (Oxidation): H(g, 1 atm) → 2H(aq, 1 M) + 2e ; E° = 0.00 V
- E°cell = E°cathode - E°anode: Used to calculate the standard potential of another electrode by connecting it with SHE.
Common Mistakes
- Students often forget the specific standard conditions (1 M H, 1 atm H, 298 K) for SHE's 0.00 V potential.
- Don't confuse the defined standard potential of SHE (0.00 V) with its potential under non-standard conditions (which is calculated using the Nernst equation).
- Misidentifying SHE's role (anode or cathode) in a galvanic cell, which depends on the relative reactivity of the other electrode.
Rapid Revision
SHE is the electrochemical reference point, defined as 0.00 V under standard conditions (1 M H, 1 atm H, 298 K). It uses an inert platinum electrode for the H/H equilibrium. Critical for measuring other standard electrode potentials by forming a cell where SHE's role (anode/cathode) depends on the partner electrode.