Problem 108
Question
Given the standard reduction potentials \(\mathrm{Zn}^{21} / \mathrm{Zn}=\) \(-0.74 \mathrm{~V}, \mathrm{Cl}_{2} / \mathrm{Cl}^{-}=1.36 \mathrm{~V}, \mathrm{H}^{\prime} / 1 / 2 \mathrm{H}_{2}=0 \mathrm{~V}\) and \(\mathrm{Fe}^{21} / \mathrm{Fe}^{3}\) \(=0.77 \mathrm{~V} .\) The order of increasing strength as reducing agent is (a) \(\mathrm{Zn}, \mathrm{H}_{2}, \mathrm{Fe}^{2+}, \mathrm{Cl}^{-}\) (b) \(\mathrm{H}_{2}, \mathrm{Zn}, \mathrm{Fe}^{2}, \mathrm{Cl}\) (c) \(\mathrm{Cl}, \mathrm{Fe}^{2+}, \mathrm{Zn}, \mathrm{H}_{2}\) (d) \(\mathrm{Cl}^{-}, \mathrm{Fe}^{2+}, \mathrm{H}_{2}, \mathrm{Zn}\)
Step-by-Step Solution
Verified Answer
The correct order is (a): \(\text{Zn}, \text{H}_2, \text{Fe}^{2+}, \text{Cl}^-\).
1Step 1: Understanding Reduction Potentials
Reduction potentials indicate the tendency of a chemical species to be reduced. The more positive the reduction potential, the greater the species' tendency to gain electrons and act as an oxidizing agent. Conversely, the more negative the reduction potential, the greater the species' tendency to lose electrons and act as a reducing agent.
2Step 2: List Given Reduction Potentials
Identify the reduction potentials provided and their respective reactions:- \( ext{Zn}^{2+} / ext{Zn} = -0.74 ext{ V}\) - \( ext{Cl}_2 / ext{Cl}^- = 1.36 ext{ V}\)- \( ext{H}^+ / rac{1}{2} ext{H}_2 = 0 ext{ V}\)- \( ext{Fe}^{2+} / ext{Fe}^{3+} = 0.77 ext{ V}\) Note: For the purposes of reducing agent strength comparison, examine only the free forms (e.g. \( ext{Zn}, ext{H}_2\)) of reactions.
3Step 3: Determine Reducing Agent Order from Reduction Potentials
The reducing agent strength is the inverse of the reduction potential order. The more negative or the smaller the reduction potential, the stronger the reducing agent. Arrange the species based on increasing reduction potential:- \( ext{Zn} (-0.74)\)- \( ext{H}_2 (0.0)\)- \( ext{Fe}^{2+} (0.77)\)- \( ext{Cl}^- (1.36)\)Thus, the order of increasing strength as reducing agents is the reverse of the reduction potentials order.
4Step 4: Match to Provided Options
Match the determined order \( ext{Zn}, ext{H}_2, ext{Fe}^{2+}, ext{Cl}^-\) to the given options. The correct answer is option (a): \( ext{Zn}, ext{H}_2, ext{Fe}^{2+}, ext{Cl}^-\).
Key Concepts
Reducing AgentsOxidizing AgentsElectrochemical Series
Reducing Agents
Reducing agents play a crucial role in chemical reactions by donating electrons to other substances. This donation of electrons leads to a reduction in the oxidation state of another chemical species. Essentially, a good reducing agent is characterized by a high propensity to lose electrons.
When assessing reducing agents using standard reduction potentials, the key point to remember is that the more negative the standard reduction potential (E°), the stronger the reducing agent. This is because such a species has a lower affinity for electrons and readily gives them up. Metals like zinc (\( \text{Zn} \)), which have negative standard reduction potentials, are commonly known as strong reducing agents.
Strong reducing agents are important in various practical applications, from industrial chemical processes to biological systems. In such contexts, they are involved in important reactions like metal extraction and biological energy conversion.
When assessing reducing agents using standard reduction potentials, the key point to remember is that the more negative the standard reduction potential (E°), the stronger the reducing agent. This is because such a species has a lower affinity for electrons and readily gives them up. Metals like zinc (\( \text{Zn} \)), which have negative standard reduction potentials, are commonly known as strong reducing agents.
Strong reducing agents are important in various practical applications, from industrial chemical processes to biological systems. In such contexts, they are involved in important reactions like metal extraction and biological energy conversion.
Oxidizing Agents
Oxidizing agents are substances that gain electrons and, in the process, oxidize another species. This means they facilitate the removal of electrons from other substances. The inherent property of oxidizing agents is their ability to accept electrons readily.
In the context of standard reduction potentials, a good oxidizing agent is identified by a more positive potential. A positive potential implies a strong tendency to be reduced, therefore acting effectively as an oxidizing agent. For example, chlorine (\( \text{Cl}_2 \)) with a high reduction potential is known to be a strong oxidizing agent.
Oxidizing agents are vital not only in chemical synthesis and industry but also in biological systems where they drive essential reactions, such as cellular respiration. Their ability to gain electrons allows for various chemical transformations necessary for life and industrial applications alike.
In the context of standard reduction potentials, a good oxidizing agent is identified by a more positive potential. A positive potential implies a strong tendency to be reduced, therefore acting effectively as an oxidizing agent. For example, chlorine (\( \text{Cl}_2 \)) with a high reduction potential is known to be a strong oxidizing agent.
Oxidizing agents are vital not only in chemical synthesis and industry but also in biological systems where they drive essential reactions, such as cellular respiration. Their ability to gain electrons allows for various chemical transformations necessary for life and industrial applications alike.
Electrochemical Series
The electrochemical series is a comprehensive list of elements and their ions arranged in order of their standard reduction potentials. This important list allows us to predict how species will behave in redox reactions.
In this series, elements are arranged from the most positive to the most negative standard reduction potentials. The more positive potential indicates a species that is likely to gain electrons (thus serve as an oxidizing agent), whereas a more negative potential highlights a species that tends to lose electrons (acting as a reducing agent).
The electrochemical series serves as a valuable tool for chemists and industry professionals as it helps predict the direction of redox reactions, determines the feasibility of constructing electrochemical cells, and aids in assessing the strength of oxidizing and reducing agents. By understanding this series, we can better grasp the relative reactivity and tendencies of different chemical species in oxidation-reduction processes.
In this series, elements are arranged from the most positive to the most negative standard reduction potentials. The more positive potential indicates a species that is likely to gain electrons (thus serve as an oxidizing agent), whereas a more negative potential highlights a species that tends to lose electrons (acting as a reducing agent).
The electrochemical series serves as a valuable tool for chemists and industry professionals as it helps predict the direction of redox reactions, determines the feasibility of constructing electrochemical cells, and aids in assessing the strength of oxidizing and reducing agents. By understanding this series, we can better grasp the relative reactivity and tendencies of different chemical species in oxidation-reduction processes.
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