Question

(a) \(\mathrm{Al}\) is oxidized and loses 3 electrons. \(\mathrm{H}\) is reduced and gains 1 electron. \(\mathrm{Al}\) is the reducing agent and \(\mathrm{HNO}_{3}\) is the oxidizing agent. (b) Ni is oxidized and loses 2 electrons. Cu is reduced and gains 2 electrons. \(\mathrm{Ni}\) is the reducing agent and \(\mathrm{CuSO}_{4}\) is the axidioing agent. (c) C is oxidized and loses 1 electron. \(O\) is reduced and gains 2 electrons. \(\mathrm{C}_{2} \mathrm{H}_{6}\) is the reducing agent and \(\mathrm{O}_{2}\) is the oxidizing agent.

Short answer

Al is oxidized losing 3e-, reducing agent; HNO3 oxidizing with H gaining 1e-. Ni oxidized losing 2e-, reducing agent; CuSO4 oxidizing with Cu gaining 2e-. C in C2H6 oxidized losing 1e-, reducing agent; O2 oxidizing with O gaining 2e-.

Step-by-step solution

Identify the Oxidation States of Aluminum and Hydrogen

In the given chemical reaction, Aluminum (Al) changes its oxidation state from 0 in its elemental form to +3 when it loses 3 electrons. Hydrogen (H), typically in compounds like HNO3, has an oxidation state of +1. When it gains 1 electron, it is reduced to its elemental form (H2), where its oxidation state is 0.

Determine the Reducing and Oxidizing Agents

Since Al loses 3 electrons, it is oxidized, making it the reducing agent as it causes another species to be reduced. HNO3 contains the hydrogen that is reduced, and thus, HNO3 is the oxidizing agent because it contains the element that accepts electrons.

Identify the Oxidation States of Nickel and Copper

Nickel (Ni) starts in its elemental form with an oxidation state of 0 and is oxidized to an oxidation state of +2 when it loses 2 electrons. Copper (Cu) in CuSO4 has an oxidation state of +2 and is reduced when it gains 2 electrons, leading to elemental copper with an oxidation state of 0.

Establish the Reducing and Oxidizing Agents for Nickel and Copper

Since Ni loses 2 electrons, it is oxidized and serves as the reducing agent. CuSO4 contains the copper that is reduced, therefore, CuSO4 is the oxidizing agent.

Identify the Oxidation States of Carbon and Oxygen

In C2H6, the carbon (C) typically has an oxidation state of -3. When oxidized, carbon loses electrons, which would increase its oxidation state. Oxygen (O), in O2, has an oxidation state of 0 and when it gains 2 electrons (per O atom), it is reduced, leading to an oxidation state of -2.

Identify the Reducing and Oxidizing Agents for Carbon and Oxygen

C2H6 acts as the reducing agent because the carbon in it is oxidized and loses electrons. O2 is the oxidizing agent because the oxygen in it is reduced and gains electrons.

Key concepts

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are fundamental chemical processes where electrons are transferred between two species. This electron transfer brings about a change in the oxidation states of the atoms involved. In a redox reaction, one substance gets oxidized by losing electrons, while another gets reduced by gaining electrons.
When looking at an example involving aluminum (Al) and hydrogen (H) in the presence of nitric acid (HNO3), we can observe that Al loses three electrons and is therefore oxidized. In this same reaction, H gains one electron and is consequently reduced. These changes in electron numbers correlate directly to the change in oxidation states. For instance, Al goes from an oxidation state of 0 to +3, indicative of its loss of electrons, while H goes from +1 to 0.
Understanding the flow of electrons helps students to visualize the overall process and the subsequent energy changes that accompany it. Redox reactions are omnipresent in both biological systems and industrial processes, making their understanding critical for a variety of scientific disciplines.

Oxidizing and Reducing Agents

In every redox reaction, there are two key players: the oxidizing agent and the reducing agent. The oxidizing agent, or oxidant, facilitates oxidation by gaining electrons and is itself reduced. Conversely, the reducing agent, or reductant, induces reduction by losing electrons and is itself oxidized. For instance, in the oxidation of nickel (Ni) to Ni^2+, Ni is the reducing agent because it loses two electrons. At the same time, the copper sulfate (CuSO4), which contains copper (Cu^2+) that gains these electrons, acts as the oxidizing agent.

Characteristics of Oxidizing and Reducing Agents

• Oxidizing agents are substances that have a strong affinity for electrons and can effectively remove them from other compounds.
• Reducing agents are species with a tendency to donate electrons.

Agents can be identified by looking at the direction of electron flow and the changes in oxidation states of the involved species. Substances like HNO3 which contain elements that accept electrons (e.g., hydrogen that goes from +1 to 0 in the reaction) are oxidizing agents, while substances like elemental Al, Ni, or organic compounds such as C2H6 that lose electrons are reducing agents. These agents are pivotal in various applications, including batteries, metallurgy, and biological systems.

Oxidation States

Oxidation states, also known as oxidation numbers, provide insight into the electron distribution within compounds. They are assigned as a theoretical charge that an atom would have if all the bonding were ionic with complete transfer of electrons. By convention, the oxidation state of an element in its standard state is zero. During a chemical reaction, the change in oxidation state tells us how many electrons are lost or gained by an atom.

Assigning Oxidation States:

• The oxidation state of pure elements is always zero.
• For a molecule like H2, each hydrogen also has an oxidation state of zero.
• In ionic compounds, such as NaCl, the Na has an oxidation state of +1, and Cl has -1, reflecting the charges in the ionic bond.

For example, in the given exercise where carbon (C) in C2H6 is oxidized, its oxidation state increases as it loses electrons. On the other hand, the oxygen (O) in O2 gains electrons and its oxidation state decreases. These state changes are integral to identifying how reactions progress, predicting the types of reactions that substances may undergo and balancing redox reactions. Mastery of the concept of oxidation states not only aids in understanding redox reactions but also enriches one's comprehension of chemical bonding and molecular structure.