Problem 2 - Chemical Principles in the Laboratory

Question

Substances \(\text{A}_{2}, \text{B}_{2}\), and \(\text{C}_{2}\) can all act as oxidizing agents. In solution, \(\text{A}_{2}\) is green, \(\text{B}_{2}\) is yellow, and \(\text{C}_{2}\) is red. In the reactions in which they participate, they are reduced to \(\text{A} ^{-}\). \(\text{B} ^{-}\), and \(\text{C}^{-}\) ions, all of which are colorless. When a solution of \(\text{C}_{2}\) is mixed with one containing \(\text{A}^{-}\) ions, the color changes from red to green. Which species is oxidized? ____________ Which is reduced? ______________ When a solution of \(C_{2}\) is mixed with one containing \(B^{-}\) ions, the color remains red. Is \(C_{2}\) a better oxidizing agent than \(A_{2} ?\) _______________ Is \(C_{2}\) a better oxidizing agent than \(B_{2} ?\) _______________ Arrange \(\text{A}_{2}, \text{B}_{2},\) and \(\text{C}_{2}\) in order of increasing strength as an oxidizing agent. \(\frac{\underline{\phantom{xx}}}{\text{Weakest oxidizing agent}} < \frac{\underline{\phantom{xx}}}{\quad\quad\quad\quad\quad} < \frac{\underline{\phantom{xx}}}{\text{Strongest oxidizing agent}}\)

Step-by-Step Solution

Answer

C_{2} is reduced; A^{-} is oxidized. No, C_{2} is not better than B_{2}. A_{2} < C_{2} < B_{2}.

Step 1: Identify Oxidation and Reduction in Reaction 1

When \(\text{C}_{2}\) is mixed with \(\text{A}^{-}\) ions and the color changes from red to green, it indicates that a chemical reaction has taken place. The red \(\text{C}_{2}\) is being reduced to colorless \(\text{C}^{-}\), and colorless \(\text{A}^{-}\) is being oxidized to green \(\text{A}_{2}\). Therefore, \(\text{A}^{-}\) is oxidized and \(\text{C}_{2}\) is reduced.

Step 2: Analyze Reaction 2 for Additional Information

When \(\text{C}_{2}\) is mixed with \(\text{B}^{-}\) ions, the solution remains red, indicating no reaction has taken place. This suggests that \(\text{B}^{-}\) is not oxidized, and therefore, \(\text{C}_{2}\) is unable to oxidize \(\text{B}^{-}\) to \(\text{B}_{2}\). Thus, \(\text{C}_{2}\) is not a stronger oxidizing agent than \(\text{B}_{2}\).

Step 3: Compare Oxidizing Strengths

From Step 1, since \(\text{C}_{2}\) can oxidize \(\text{A}^{-}\) to \(\text{A}_{2}\), \(\text{C}_{2}\) is a stronger oxidizing agent than \(\text{A}_{2}\). From Step 2, \(\text{C}_{2}\) is not a stronger oxidizing agent than \(\text{B}_{2}\). Therefore, the order of increasing oxidizing strength is: \(\text{A}_{2} < \text{C}_{2} < \text{B}_{2}\).

Key Concepts

Oxidizing Agents

An oxidizing agent is a substance that can accept electrons from another substance during a chemical reaction. This process causes the oxidizing agent to be reduced while the other substance is oxidized. In simple terms, the oxidizing agent is what gets reduced in the reaction. Oxidizing agents play a crucial role in oxidation-reduction reactions, commonly called redox reactions.

In our exercise,

• Substances \(\text{A}_{2}\), \(\text{B}_{2}\), and \(\text{C}_{2}\) act as oxidizing agents.
• They accept electrons and are reduced to colorless ions \(\text{A}^{-}\), \(\text{B}^{-}\), and \(\text{C}^{-}\) respectively.

The strength of an oxidizing agent can vary. In the given steps, \(\text{C}_{2}\) can oxidize \(\text{A}^{-}\) but not \(\text{B}^{-}\), indicating a hierarchy of oxidizing strength. This shows that not all oxidizing agents have the same capability to drive other species to lose electrons.

Chemical Reactions

Chemical reactions involve the transformation of substances through breaking and forming bonds, resulting in different substances with new properties. Redox reactions are a type of chemical reaction where oxidation states change due to electron transfer between species.

In the given exercise, when \(\text{C}_{2}\) is mixed with \(\text{A}^{-}\) ions, a redox reaction occurs:

• The red \(\text{C}_{2}\) gets reduced to colorless \(\text{C}^{-}\).
• The colorless \(\text{A}^{-}\) ions are oxidized to green \(\text{A}_{2}\).

This change in color indicates that a chemical transformation has taken place. However, when \(\text{C}_{2}\) is mixed with \(\text{B}^{-}\) ions, no reaction occurs, showing that not all combinations of substances will react. The color remaining red indicates that the chemical properties of \(\text{C}_{2}\) and \(\text{B}^{-}\) do not support a redox process under these conditions.

Oxidation States

Oxidation states, or oxidation numbers, are values that help us track the electron transfers in a chemical reaction. An increase in oxidation state indicates oxidation (loss of electrons), while a decrease indicates reduction (gain of electrons). This concept is pivotal in analyzing redox reactions.

In the exercise, the substances' transition from \(\text{C}_{2}\) to \(\text{C}^{-}\) or \(\text{A}^{-}\) to \(\text{A}_{2}\) involves changes in their oxidation states:

• \(\text{C}_{2}\) being reduced to \(\text{C}^{-}\) means its oxidation state decreases as it gains electrons.
• \(\text{A}^{-}\) being oxidized to \(\text{A}_{2}\) means its oxidation state increases as it loses electrons.

Understanding oxidation states allows us to determine which species in a reaction are undergoing oxidation or reduction. It serves as a tool to predict the direction of electron transfer and rank oxidizing agents by their relative strength in a redox reaction.