Question

Identify the oxidized reactant, the reduced reactant, the oxidizing agent, and the reducing agent in the following reactions: (a) \(\mathrm{Fe}(s)+\mathrm{Cu}^{2+}(a q) \longrightarrow \mathrm{Fe}^{2+}(a q)+\mathrm{Cu}(s)\) (b) \(\mathrm{Mg}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{MgCl}_{2}(s)\) (c) \(2 \mathrm{Al}(s)+\mathrm{Cr}_{2} \mathrm{O}_{3}(s) \longrightarrow 2 \mathrm{Cr}(s)+\mathrm{Al}_{2} \mathrm{O}_{3}(s)\)

Short answer

(a) Oxidized: Fe, Reduced: Cu²⁺, Oxidizing agent: Cu²⁺, Reducing agent: Fe. (b) Oxidized: Mg, Reduced: Cl₂, Oxidizing agent: Cl₂, Reducing agent: Mg. (c) Oxidized: Al, Reduced: Cr₂O₃, Oxidizing agent: Cr₂O₃, Reducing agent: Al.

Step-by-step solution

Determine oxidation states for Reaction (a)

In reaction (a), \(\mathrm{Fe}(s) + \mathrm{Cu}^{2+}(aq) \rightarrow \mathrm{Fe}^{2+}(aq) + \mathrm{Cu}(s)\): - Solid iron \((\mathrm{Fe})\) has an oxidation state of 0.- Copper \((\mathrm{Cu}^{2+})\) has an oxidation state of +2.- \(\mathrm{Fe}^{2+}\) becomes +2, meaning it has lost 2 electrons (oxidized).- \(\mathrm{Cu}\) goes from +2 in \(\mathrm{Cu}^{2+}\) to 0, meaning it gains 2 electrons (reduced).

Identify components for Reaction (a)

In reaction (a): - **Oxidized reactant** is \(\mathrm{Fe}\) because its oxidation state increases from 0 to +2.- **Reduced reactant** is \(\mathrm{Cu}^{2+}\) because its oxidation state decreases from +2 to 0.- **Oxidizing agent** is \(\mathrm{Cu}^{2+}\) as it gains electrons.- **Reducing agent** is \(\mathrm{Fe}\) as it loses electrons.

Determine oxidation states for Reaction (b)

In reaction (b), \(\mathrm{Mg}(s) + \mathrm{Cl_2}(g) \rightarrow \mathrm{MgCl_2}(s)\): - Magnesium \((\mathrm{Mg})\) has an oxidation state of 0.- Chlorine \((\mathrm{Cl_2})\) has an oxidation state of 0.- In \(\mathrm{MgCl_2}\), \(\mathrm{Mg}\) becomes +2 and each \(\mathrm{Cl}\) becomes -1.- \(\mathrm{Mg}\) loses 2 electrons and \(\mathrm{Cl_2}\) gains electrons.

Identify components for Reaction (b)

In reaction (b):- **Oxidized reactant** is \(\mathrm{Mg}\) because its oxidation state increases from 0 to +2.- **Reduced reactant** is \(\mathrm{Cl_2}\) because its oxidation state decreases from 0 to -1.- **Oxidizing agent** is \(\mathrm{Cl_2}\) as it gains electrons.- **Reducing agent** is \(\mathrm{Mg}\) as it loses electrons.

Determine oxidation states for Reaction (c)

In reaction (c), \(2 \mathrm{Al}(s) + \mathrm{Cr_2 O_3}(s) \rightarrow 2 \mathrm{Cr}(s) + \mathrm{Al_2 O_3}(s)\): - Aluminum \((\mathrm{Al})\) has an oxidation state of 0.- Chromium \((\mathrm{Cr})\) in \(\mathrm{Cr_2O_3}\) is +3 and the oxide ion \((\mathrm{O})\) is -2.- In \(\mathrm{Al_2O_3}\), \(\mathrm{Al}\) is +3.- \(\mathrm{Cr}\) in \(\mathrm{Cr_2O_3}\) becomes 0 in \(\mathrm{Cr}\).

Identify components for Reaction (c)

In reaction (c):- **Oxidized reactant** is \(\mathrm{Al}\) because its oxidation state increases from 0 to +3.- **Reduced reactant** is \(\mathrm{Cr_2O_3}\) because \(\mathrm{Cr}\) reduces from +3 to 0.- **Oxidizing agent** is \(\mathrm{Cr_2O_3}\) as it gains electrons.- **Reducing agent** is \(\mathrm{Al}\) as it loses electrons.

Key concepts

Oxidation States

Oxidation states, also known as oxidation numbers, are theoretical charges assigned to atoms within a molecule to indicate the degree of oxidation or reduction. They provide a way to keep track of electrons during chemical reactions. By determining the oxidation states of atoms in both the reactants and products, one can identify which atoms have gained or lost electrons. This helps to clarify the changes occurring in redox reactions.

• Oxidation refers to an increase in oxidation state, which corresponds to the loss of electrons.
• Reduction refers to a decrease in oxidation state, indicating the gain of electrons.

Understanding oxidation states is crucial for correctly identifying the processes and agents in redox reactions.

Oxidizing Agent

An oxidizing agent is a substance that promotes the oxidation of another species during a chemical reaction by gaining electrons itself. In doing so, it undergoes reduction.
In redox reactions, identifying the oxidizing agent involves finding the molecule or ion that has gained electrons and, therefore, experienced a reduction in its oxidation state.

• Example: In reaction (a), \({\text{Cu}^{2+}}\) serves as the oxidizing agent because it gains 2 electrons, reducing its oxidation state from +2 to 0.

The ability to identify the oxidizing agent is essential for understanding how electron transfer manifests in chemical processes.

Reducing Agent

A reducing agent, or reductant, is the opposite of the oxidizing agent. It donates electrons to another species, facilitating reduction, while itself undergoing oxidation.
In redox reactions, the reducing agent can be recognized as the species whose oxidation state increases, as it loses electrons.

• For example, in reaction (b), magnesium (Mg) acts as the reducing agent since it loses 2 electrons, increasing its oxidation state from 0 to +2.

Identifying the reducing agent helps to comprehend which components are donating electrons and undergoing oxidation within a reaction.

Electron Transfer

Electron transfer is at the heart of redox reactions. It involves the movement of electrons from one atom or molecule to another, leading to changes in oxidation states and the reconfiguration of bonds.

• An oxidation process involves the loss of electrons by a species, increasing its oxidation state.
• A reduction process, on the other hand, involves the gain of electrons, decreasing its oxidation state.

For instance, during the electron transfer in reaction (c), aluminum (Al) loses electrons, while chromium (Cr) gains electrons. This transfer forms the basis of identifying oxidized and reduced species, as well as oxidizing and reducing agents.

Chemical Reactions

Chemical reactions involve the rearrangement of atoms and bonds to form new substances. Redox reactions, a specific type of chemical reaction, focus on the exchange of electrons between reactants.

• These reactions are essential in processes such as combustion, corrosion, and energy production.
• Balancing redox reactions includes ensuring that the number of electrons lost equals the number of electrons gained, maintaining charge balance.

Understanding the fundamental principles of chemical reactions, like balancing and electron transfer, offers insights into how substances interact and transform.