Which is not true for a standard hydrogen electrode ?

Q: Which is not true for a standard hydrogen electrode ?

Which is not true for a standard hydrogen electrode ?

Question

Accepted Answer

Explanation:

1. **Option 4: It contains a metallic conductor which does not adsorb hydrogen.**  
   This statement is not true for a standard hydrogen electrode (SHE). In a standard hydrogen electrode, the metallic conductor used is typically platinum. Platinum is chosen because it has excellent catalytic properties and can adsorb hydrogen gas. This adsorption is crucial as it facilitates the establishment of equilibrium between hydrogen ions in solution and hydrogen gas at the electrode surface. Therefore, the statement that the metallic conductor does not adsorb hydrogen is incorrect, making Option 4 the correct choice for what is not true about a standard hydrogen electrode.

2. **Option 1: The hydrogen ion concentration is 1 M.**  
   This statement is true for a standard hydrogen electrode. The SHE is defined under standard conditions, which include a hydrogen ion concentration of 1 M. This concentration ensures that the electrode potential is measured under consistent and reproducible conditions.

3. **Option 2: Temperature is $25^{\circ}C$.**  
   This statement is also true for a standard hydrogen electrode. The standard conditions for electrochemical measurements, including those for the SHE, are set at a temperature of $25^{\circ}C$ (298 K). This standard temperature is used to maintain consistency across different experiments and measurements.

4. **Option 3: Pressure of hydrogen is 1 bar.**  
   This statement is true for a standard hydrogen electrode. The pressure of hydrogen gas in the SHE is maintained at 1 bar (or 1 atmosphere in older conventions) to ensure that the electrode potential is measured under standard conditions. This pressure is crucial for maintaining the equilibrium between the gaseous hydrogen and the hydrogen ions in solution.

In summary, Option 4 is the correct answer because it inaccurately describes the properties of a standard hydrogen electrode, specifically regarding the adsorption of hydrogen by the metallic conductor. The other options correctly describe the standard conditions of a SHE.