Problem 98 - Chemistry The Science in Context

Question

Electron gain is associated with _______ half-reactions, and electron loss is associated with ______ half-reactions.

Step-by-Step Solution

Answer

Answer: Electron gain is associated with reduction half-reactions, and electron loss is associated with oxidation half-reactions.

Step 1: STEP 1: Identify the process associated with electron gain.

Electron gain occurs in reduction half-reactions. During a reduction process, the species involved gains electrons, which causes its oxidation state to decrease.

Step 2: STEP 2: Identify the process associated with electron loss.

Electron loss occurs in oxidation half-reactions. During an oxidation process, the species involved loses electrons, which causes its oxidation state to increase.

Step 3: STEP 3: Provide the answer to the exercise.

Electron gain is associated with reduction half-reactions, and electron loss is associated with oxidation half-reactions.

Key Concepts

Oxidation

Oxidation is a fundamental part of redox reactions where a chemical species loses electrons. This loss of electrons results in an increase in the oxidation state of the element. Simply put, as a molecule, atom, or ion sheds electrons, it is said to undergo oxidation.

• When a substance gives away electrons, its charge becomes more positive.
• Oxidation does not necessarily involve oxygen, though traditionally it was associated with combining with oxygen.

This can seem counterintuitive because oxidation originally referred to reactions with oxygen. However, in modern chemistry, it has broadened to mean the loss of electrons, regardless of the involvement of oxygen. Suppose we have a reaction where iron atoms lose electrons to form iron ions: Fe → Fe³⁺ + 3e⁻. In this example, iron is oxidized.
A mnemonic to remember this process is "OIL RIG," which stands for "Oxidation Is Loss" of electrons.

Reduction

Reduction is the opposite process of oxidation in redox reactions. Here, a chemical species gains electrons, leading to a decrease in its oxidation state.

• This gain of electrons makes the charge more negative.
• For instance, in the reduction of copper ions to copper metal, Cu²⁺ + 2e⁻ → Cu, copper ions gain electrons to form copper atoms.

The term reduction can be remembered by considering that gaining electrons causes a "reduction" in positive charge. Just as with oxidation, the changes in electron count directly correspond to changes in oxidation states. Reduction can sometimes be less intuitive, but remembering that it involves the gain of electrons helps simplify understanding.
It is the "RIG" part of the mnemonic "OIL RIG," meaning "Reduction Is Gain" of electrons.

Half-reactions

Half-reactions are used to break down redox reactions into their individual oxidation and reduction components. This allows for a clearer understanding of how electrons are transferred between chemical species during a reaction.

• An oxidation half-reaction shows the loss of electrons from a species.
• A reduction half-reaction displays the gain of electrons by a species.

For example, in the complete redox reaction of zinc and copper sulfate Zn + CuSO₄ → ZnSO₄ + Cu, the half-reactions are: - Oxidation: Zn → Zn²⁺ + 2e⁻ - Reduction: Cu²⁺ + 2e⁻ → Cu Breaking these reactions down emphasizes the transfer of electrons between reacting species.
Half-reactions are a powerful tool for balancing redox equations, as they provide a visual and mathematical way to ensure that the number of electrons lost equals the number of electrons gained.