Question

For each of the following reactions, identify the oxidizing agent and the reducing agent: a. \(\mathrm{C}_{2} \mathrm{H}_{2}+\mathrm{H}_{2} \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}\) b. \(\mathrm{H}_{2} \mathrm{CO}+\mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow \mathrm{H}_{2} \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\) c. \(\mathrm{Fe}_{2} \mathrm{O}_{3}+3 \mathrm{CO} \longrightarrow 2 \mathrm{Fe}+3 \mathrm{CO}_{2}\)

Short answer

a. Oxidizing agent: \(\mathrm{C}_2\mathrm{H}_2\), Reducing agent: \(\mathrm{H}_2\). b. Oxidizing agent: \(\mathrm{H}_2\mathrm{O}_2\), Reducing agent: \(\mathrm{H}_2\mathrm{CO}\). c. Oxidizing agent: \(\mathrm{Fe}_2\mathrm{O}_3\), Reducing agent: \(\mathrm{CO}\).

Step-by-step solution

- Understand Oxidation and Reduction

Understand that oxidation is the loss of electrons, resulting in an increase in oxidation state. Reduction is the gain of electrons, resulting in a decrease in the oxidation state. An oxidizing agent is a substance that oxidizes another substance by accepting electrons, therefore it is reduced. A reducing agent is a substance that reduces another substance by donating electrons, therefore it is oxidized.

- Analyze Reaction a

Write down the oxidation states for atoms in \(\mathrm{C}_2\mathrm{H}_2\) and \(\mathrm{C}_2\mathrm{H}_4\). Carbon in \(\mathrm{C}_2\mathrm{H}_2\) goes from an oxidation state of -1 to -2 in \(\mathrm{C}_2\mathrm{H}_4\), thus getting reduced and hydrogen goes from 0 in \(\mathrm{H}_2\) to -1 in \(\mathrm{C}_2\mathrm{H}_4\), thus getting oxidized. Hence, \(\mathrm{C}_2\mathrm{H}_2\) is the oxidizing agent and \(\mathrm{H}_2\) is the reducing agent.

- Analyze Reaction b

Assign oxidation states to the atoms in \(\mathrm{H}_2\mathrm{CO}\) and \(\mathrm{H}_2\mathrm{CO}_2\). The carbon atom in \(\mathrm{H}_2\mathrm{CO}\) goes from an oxidation state of +1 to +4 in \(\mathrm{H}_2\mathrm{CO}_2\). Since the carbon in the formaldehyde (\(\mathrm{H}_2\mathrm{CO}\)) is oxidized, \(\mathrm{H}_2\mathrm{CO}\) is the reducing agent. Oxygen in \(\mathrm{H}_2\mathrm{O}_2\) goes from -1 to -2 in \(\mathrm{H}_2\mathrm{O}\), thus it is reduced and \(\mathrm{H}_2\mathrm{O}_2\) is the oxidizing agent.

- Analyze Reaction c

Determine the oxidation states of iron and carbon in the reactants and products. The iron in \(\mathrm{Fe}_2\mathrm{O}_3\) goes from +3 to 0, which means it is reduced, making \(\mathrm{Fe}_2\mathrm{O}_3\) the oxidizing agent. Carbon in \(\mathrm{CO}\) goes from +2 to +4 in \(\mathrm{CO}_2\), meaning it is oxidized, so \(\mathrm{CO}\) is the reducing agent.

Key concepts

Oxidizing and Reducing Agents

Understanding the roles of oxidizing and reducing agents is crucial in determining the direction of a chemical reaction. An oxidizing agent, often referred to as the electron acceptor, is responsible for the oxidation of another substance and itself gets reduced. Conversely, a reducing agent donates electrons to another compound, causing itself to be oxidized in the process.

In the analysis of the given reactions, for instance in reaction a, \(\mathrm{C}_2\mathrm{H}_2\) serves as an oxidizing agent by accepting electrons during the reaction, thus getting reduced. On the other hand, \(\mathrm{H}_2\) acts as the reducing agent because it donates electrons and is oxidized. Identifying these agents helps in predicting the outcome of the reaction and in understanding the movement of electrons during the process.

It's useful to remember that oxidizing agents often contain elements in high oxidation states, like oxygen or halogens, or noble metals that can take on a higher positive charge, while reducing agents typically include metals in low oxidation states or hydrides.

Assigning Oxidation States

The proper assignment of oxidation states to atoms within a molecule is key to understanding redox reactions. Oxidation state, or oxidation number, is a theoretical charge that an atom would have if electrons were distributed according to a set of rules. These rules include assigning an oxidation state of zero to elements in their natural state, negative values to more electronegative atoms in compounds, and specific values to atoms in common groups, like +1 for hydrogen and -2 for oxygen, with some exceptions.

As an example, in reaction b, assigning the oxidation states allows us to see that carbon in \(\mathrm{H}_2\mathrm{CO}\) increases its oxidation state from +1 to +4 when going to \(\mathrm{H}_2\mathrm{CO}_2\), indicating it is being oxidized. Following these guidelines consistently is vital for correctly identifying the changes in oxidation that accompany chemical transformations.

Redox Reactions Analysis

The analysis of redox reactions involves scrutinizing the changes in oxidation states and identifying which substances are oxidized and reduced. Redox reactions are the backbone of many chemical processes, including combustion, corrosion, and energy production in batteries.

For instance, in reaction c, one can observe that iron in \(\mathrm{Fe}_2\mathrm{O}_3\) is reduced as its oxidation state decreases from +3 to 0 upon forming metallic iron (Fe). In contrast, carbon monoxide (CO) is oxidized to carbon dioxide (CO2), evidenced by an increase in its carbon's oxidation state from +2 to +4. This analysis not only explains what happens at a molecular level but also helps predict the amounts of substances produced or required in a given reaction, which is an essential aspect of stoichiometry and practical chemistry.