Question

Explain why \(\mathrm{SO}_{2}\) can be used as a reducing agent but \(\mathrm{SO}_{3}\) cannot.

Short answer

SO₂ can be used as a reducing agent because it can donate electrons and be oxidized to SO₃, where sulfur has its highest oxidation state of +6. In contrast, SO₃ cannot act as a reducing agent since sulfur is already in its highest oxidation state and cannot be further oxidized or donate electrons.

Step-by-step solution

Understand Reducing Agents

A reducing agent is a substance that can reduce other substances, which means it can donate electrons to other substances during a chemical reaction. Reducing agents themselves are oxidized in the process, meaning they lose electrons. To determine if a molecule can act as a reducing agent, we should examine its ability to donate electrons and its willingness to be oxidized.

Examine Oxidation States and Stability of SO₂

In SO₂, the sulfur atom has an oxidation state of +4. SO₂ is able to be oxidized further to SO₃, in which sulfur has the oxidation state of +6, the highest possible oxidation state for sulfur. In this process, SO₂ donates electrons to other molecules, reducing them and becoming more oxidized itself: SO₂ + ½ O₂ → SO₃ Thus, SO₂ can act as a reducing agent, as it can donate electrons and be oxidized.

Examine Oxidation States and Stability of SO₃

In SO₃, the sulfur atom has the oxidation state of +6. This is the highest possible oxidation state for sulfur, meaning SO₃ cannot be oxidized further. Since it cannot be further oxidized, SO₃ has no electrons to donate and cannot act as a reducing agent.

Compare SO₂ and SO₃

Comparing the oxidation states and stability of SO₂ and SO₃, it is clear that SO₂ can act as a reducing agent because it is capable of donating electrons while being oxidized to SO₃. In contrast, SO₃ is already in its highest oxidation state and cannot be further oxidized, making it unable to act as a reducing agent. Overall: SO₂ can be used as a reducing agent due to its ability to donate electrons and be oxidized to SO₃, while SO₃ cannot be used as a reducing agent because it is already in its highest oxidation state and cannot be further oxidized.