Problem 15 - Chemistry The Central Science

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

(a) True; (b) False; (c) True.

Step 1: Statement (a)

Is "If something is oxidized, it is formally losing electrons" true or false? In a redox reaction, when a reactant is oxidized, it formally loses electrons as it has an increase in its oxidation state. Therefore, this statement is true.

Step 2: Statement (b)

Is "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" true or false? First, identify which elements are being oxidized and which are being reduced: - \(\mathrm{Fe}^{3+}(a q)\) is reduced to \(\mathrm{Fe}^{2+}(a q)\) because its oxidation state decreases from +3 to +2. - \(\mathrm{Co}^{2+}(a q)\) is oxidized to \(\mathrm{Co}^{3+}(a q)\) because its oxidation state increases from +2 to +3. A reducing agent is a substance that causes the reduction of another substance, meaning it provides electrons to the other species. In this case, \(\mathrm{Fe}^{3+}(a q)\) is the species being reduced, and \(\mathrm{Co}^{2+}(a q)\) is the species that is providing the electrons for this reduction to happen, so \(\mathrm{Co}^{2+}(a q)\) is the reducing agent. An oxidizing agent is a substance that causes the oxidation of another substance, meaning it takes electrons from the other species. In this case, \(\mathrm{Co}^{2+}(a q)\) is the species being oxidized, and \(\mathrm{Fe}^{3+}(a q)\) is the species taking electrons from Cobalt, so \(\mathrm{Fe}^{3+}(a q)\) is the oxidizing agent. Therefore, this statement is false because it incorrectly states the roles of \(\mathrm{Fe}^{3+}(a q)\) and \(\mathrm{Co}^{2+}(a q)\).

Step 3: Statement (c)

Is "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" true or false? In a redox reaction, there is always a change in the oxidation state of at least one element in the reactants and products, since the exchange of electrons is occurring in the reaction. If there are no changes in the oxidation states of the elements in a reaction, then it cannot be a redox reaction. Therefore, this statement is true.

Key Concepts

Oxidizing Agent

In redox reactions, the oxidizing agent plays a crucial role by facilitating the loss of electrons from another substance. Essentially, the oxidizing agent **takes** electrons from another substance, causing that substance to be oxidized. As it takes electrons, the oxidizing agent itself is reduced.
For example, in the discussed reaction where \[\mathrm{Fe}^{3+}(aq) + \mathrm{Co}^{2+}(aq) \longrightarrow \mathrm{Fe}^{2+}(aq) + \mathrm{Co}^{3+}(aq),\]iron ions, \(\mathrm{Fe}^{3+}(aq), \)act as the oxidizing agent. This is because it accepts electrons from cobalt ions, \(\mathrm{Co}^{2+}(aq),\)which leads to the decrease in its oxidation state from +3 to +2.
This acceptance of electrons enables the cobalt ions to be oxidized from a +2 to a +3 oxidation state. Remember, without an oxidizing agent, the oxidation process could not occur. The oxidizing agent essentially drives the electron exchange that defines redox reactions.

Reducing Agent

In a redox reaction, the reducing agent donates electrons to another substance. Through this act of donating electrons, the reducing agent itself undergoes oxidation. This dual activity makes the reducing agent essential in the redox process.
The reducing agent facilitates the reduction of another species by supplying the necessary electrons for the reduction to take place. In the example reaction:\[\mathrm{Fe}^{3+}(aq) + \mathrm{Co}^{2+}(aq) \longrightarrow \mathrm{Fe}^{2+}(aq) + \mathrm{Co}^{3+}(aq),\]\(\mathrm{Co}^{2+}(aq)\)serves as the reducing agent. It provides electrons to \(\mathrm{Fe}^{3+}(aq),\)leading to its reduction to \(\mathrm{Fe}^{2+}(aq).\)
By volunteering its electrons, \(\mathrm{Co}^{2+}(aq)\)transforms into \(\mathrm{Co}^{3+}(aq),\)thereby undergoing oxidation. The reducing agent is integral because it sets the stage for the necessary oxidation-reduction dance, making the exchange of electrons possible.

Oxidation State Changes

A redox reaction is characterized by changes in the oxidation states of the molecules involved. These changes indicate how electrons are distributed among the different species before and after the reaction. Understanding how these changes occur is essential in identifying redox reactions.
To determine if a reaction is a redox reaction, look for a transfer of electrons which is signified by a change in oxidation states. If, during a reaction, at least one species undergoes a change in its oxidation state, where it either loses or gains electrons, this indicates a redox process.
For instance, consider if no changes in oxidation state occur, like in the reaction: - The reactants' oxidation states remain unchanged. If this scenario occurs, it confirms the absence of a redox reaction because no electrons have been exchanged. Such stability in oxidation states confirms the initial proposition, declaring that the presence of electron transfer—as evidenced by changing oxidation states—is vital to identify a true redox reaction.