Question

Hydrogen peroxide, H₂O₂, can act as both an oxidising agent or a reducing agent according to the following half reactions:

Oxidising agent: H₂O₂(aq) + 2H⁺(aq) +2e^– → 2H₂O(l)
Reducing agent: H₂O₂(aq) → O₂(g) + 2H⁺(aq) 2e^–

What simple visual cue would indicate a reaction where H₂O₂ is acting as a reducing agent?

		formation of water
		increase in pH
		appearance of electrons
		bubbles of gas

Answer 1

When H₂O₂ is acting as a reducing agent, i.e. H₂O₂ itself is undergoing oxidation, exactly saying, the oxidation state of oxygen is converting from -1 (in H₂O₂) to 0 (in O₂).

i.e. The increase in oxidation state/oxidation no. of oxygen occurs.

The balanced reaction is given as: H₂O₂(aq) → O₂(g) + 2H⁺(aq) + 2e^–

Here, the simple visual clue in the reaction, where H₂O₂ is acting as a reducing agent can be an appearance of electrons. (One of the definitions of oxidation says that the loss of electrons takes place during the oxidation reaction.)