Which ions are reduced when hydrogen gas is bubbled into a solution containing both Fe(II) and Fe(III) ions?

When hydrogen gas is introduced into a solution containing both Fe(II) and Fe(III) ions, the relevant reduction process involves the conversion of higher oxidation state ions into lower oxidation state ions. In this case, Fe(III) ions (Fe³⁺) are more oxidized compared to Fe(II) ions (Fe²⁺). The reduction involves the gaining of electrons, and since hydrogen gas can serve as a reducing agent, the Fe(III) ions are reduced to Fe(II).

In electrochemical terms, the reduction half-reaction for iron could be represented as:

Fe³⁺ + e⁻ → Fe²⁺

This process shows that Fe(III) ions are the species that gain electrons, transitioning from a higher oxidation state to a lower one, which is indicative of reduction. Therefore, when hydrogen gas is bubbled into the solution, it facilitates this reduction process by donating electrons to the more oxidized Fe(III) ions.

While H⁺ ions could theoretically be reduced in the presence of another reducing agent, in this specific scenario with Fe ions present, the reduction of Fe³⁺ to Fe²⁺ takes precedence due to the lower potential required for its reduction compared to that