Question

I have read in textbooks and websites that hydrogen gas needs to be bubbled into the SHE (Standard Hydrogen Electrode). I understand why for oxidation of the half cell - the gas is oxidised into H+ (aq) and the electrons move into the other half cell. Anions from the salt bridge then move to maintain cell neutrality.

However, I fail to understand why hydrogen gas needs to be bubbled into the cell during reduction, as hydrogen intake is not needed. As H+ (aq) gets reduced into gas, it will just bubble out whereever it is formed, not necessarily through the tube. Cations from the salt bridge move to maintain neutrality.

I suspect that it is something to do to maintain stability/neutrality. Can anyone please help?

Answer 1

Bubbling hydrogen gas into the SHE during reduction maintains the standard conditions of 1 atm pressure and a constant concentration of H+ ions at 1 M, ensuring accurate potential measurements by providing a consistent reaction interface.

Step-by-step explanation:

The need to bubble hydrogen gas into the Standard Hydrogen Electrode (SHE) during reduction is due to the necessity of maintaining a constant pressure of hydrogen gas at 1 atm and providing a consistent surface area for the reaction to occur. The interfaces at which these reactions take place are important for accurate, reproducible measurements.

In the case of the SHE, the platinum surface acts as a catalyst and also provides a surface where the equilibrium between H2 and H+ ions can be established. This consistency is very important for maintaining the standard conditions under which the potential is defined to be 0 V.

Additionally, having a constant flow of hydrogen gas ensures the concentration of H+ ions remains at 1 M due to the equilibrium, which is crucial for accurately comparing half-reaction potentials in electrochemistry.