Problem 15 - Chemistry: The Central Science in SI Units, Global Edition

Question

Indicate whether each of the following statements is true or false: (a) If something is oxidized, it is formally losing electrons. (b) For the reaction \(\mathrm{Fe}^{3+}(a q)+\mathrm{Co}^{2+}(a q) \longrightarrow \mathrm{Fe}^{2+}(a q)+\) \(\mathrm{Co}^{3+}(a q), \mathrm{Fe}^{3+}(a q)\) is the reducing agent and \(\mathrm{Co}^{2+}(a q)\) is the oxidizing agent. (c) If there are no changes in the oxidation state of the reactants or products of a particular reaction, that reaction is not a redox reaction.

Step-by-Step Solution

Answer

Short Answer: Statement (a): True Statement (b): False Statement (c): True

Step 1: Statement (a) Analysis: If something is oxidized, it is formally losing electrons.

Recall the concept of oxidation and reduction in redox reactions: - Oxidation refers to the loss of electrons. - Reduction refers to the gain of electrons. Since the statement says that if something is oxidized, it is formally losing electrons, the statement is correct. Thus, the answer is: Statement (a): True

Step 2: Statement (b) Analysis: Reducing and Oxidizing Agents in the Reaction of \(\mathrm{Fe}^{3+}\) and \(\mathrm{Co}^{2+}\)

In the given reaction: \(\mathrm{Fe}^{3+}(a q)+\mathrm{Co}^{2+}(a q) \longrightarrow \mathrm{Fe}^{2+}(a q)+\mathrm{Co}^{3+}(a q)\) We need to find the change in oxidation state of \(\mathrm{Fe}\) and \(\mathrm{Co}\) : - \(\mathrm{Fe}\): \(\mathrm{Fe}^{3+}(aq)\) has an oxidation state of +3 and \(\mathrm{Fe}^{2+}(aq)\) has an oxidation state of +2, so the change is (-1), which means reduction has occurred. - \(\mathrm{Co}\): \(\mathrm{Co}^{2+}(aq)\) has an oxidation state of +2 and \(\mathrm{Co}^{3+}(aq)\) has an oxidation state of +3, so the change is (+1), which means oxidation has occurred. Now, we can identify the reducing and oxidizing agents: - Reducing agent: The substance that reduces another substance by losing electrons (undergoes oxidation). In this case, it is \(\mathrm{Co}^{2+}(aq)\). - Oxidizing agent: The substance that oxidizes another substance by gaining electrons (undergoes reduction). In this case, it is \(\mathrm{Fe}^{3+}(aq)\). Therefore, the claim that \(\mathrm{Fe}^{3+}(a q)\) is the reducing agent and \(\mathrm{Co}^{2+}(a q)\) is the oxidizing agent is incorrect. Thus, the answer is: Statement (b): False

Step 3: Statement (c) Analysis: No Change in Oxidation State for Reactants or Products

The statement claims that if there are no changes in the oxidation state of the reactants or products in a reaction, it is not a redox reaction. Remember that redox reactions involve oxidation and reduction processes, where one substance loses electrons and another gains electrons. Therefore, if no changes in oxidation state occur, then neither oxidation nor reduction has taken place, and the reaction is not a redox reaction. Thus, the answer is: Statement (c): True

Key Concepts

Oxidation

Oxidation is a core concept in redox reactions, often remembered as the process where a substance loses electrons. This can be understood through the acronym OIL, which stands for "Oxidation Is Loss." When a chemical species loses electrons during a chemical reaction, its oxidation state increases. For example, in the reaction involving ```\(\mathrm{Fe}^{3+}(aq)+\mathrm{Co}^{2+}(aq)\rightarrow \mathrm{Fe}^{2+}(aq)+\mathrm{Co}^{3+}(aq)\) ```the cobalt ion, \(\mathrm{Co}^{2+}\), undergoes oxidation by losing an electron to become \(\mathrm{Co}^{3+}\). This loss of electrons is what defines oxidation in any redox reaction.

Reduction

Reduction is the counter-process to oxidation in redox reactions. It occurs when a substance gains electrons, which results in a decrease in its oxidation state. Remember RIG, which stands for "Reduction Is Gain," to help associate this process with the gaining of electrons. In the earlier example of the reaction between iron and cobalt ions, ```\(\mathrm{Fe}^{3+}\) gains an electron to become \(\mathrm{Fe}^{2+}\)```. This gain of an electron means that iron is reduced in the reaction. Reduction is always paired with oxidation because electrons lost by one species are gained by another.

Oxidizing Agent

An oxidizing agent is a crucial player in redox reactions. It is the substance that oxidizes another by accepting its electrons. In simple terms, the oxidizing agent gets reduced in the reaction. For instance, in the given chemical reaction: ```\(\mathrm{Fe}^{3+}(aq) + \mathrm{Co}^{2+}(aq) \rightarrow \mathrm{Fe}^{2+}(aq) + \mathrm{Co}^{3+}(aq)\) ```\(\mathrm{Fe}^{3+}\) acts as the oxidizing agent because it accepts an electron from \(\mathrm{Co}^{2+}\) and gets reduced to \(\mathrm{Fe}^{2+}\). Thus, identifying the oxidizing agent is crucial as it highlights the electron transfer process.

Reducing Agent

The reducing agent is the opposite counterpart to the oxidizing agent in a redox reaction. It donates electrons to another substance, thereby reducing the other substance and itself getting oxidized in the process. In our example reaction: ```\(\mathrm{Fe}^{3+}(aq) + \mathrm{Co}^{2+}(aq) \rightarrow \mathrm{Fe}^{2+}(aq) + \mathrm{Co}^{3+}(aq)\)```\(\mathrm{Co}^{2+}\) acts as the reducing agent as it donates an electron to \(\mathrm{Fe}^{3+}\) and gets oxidized to \(\mathrm{Co}^{3+}\). Recognizing the reducing agent helps in understanding which substances are undergoing oxidation and reduction.