Question

(a) Use the following reactions to arrange the elements \(\mathbf{A}, \mathbf{B}, \mathbf{C}\), and \(\mathbf{D}\) in order of their decreasing ability as reducing agents: \(2 \mathrm{~A}+\mathrm{B}^{2+} \longrightarrow 2 \mathrm{~A}^{+}+\mathrm{B} \quad \mathrm{B}+\mathrm{D}^{2+} \longrightarrow \mathrm{B}^{2+}+\mathrm{D}\) \(\mathrm{A}^{+}+\mathrm{C} \longrightarrow\) no reaction \(2 \mathrm{C}+\mathrm{B}^{2+} \longrightarrow 2 \mathrm{C}^{+}+\mathrm{B}\) (b) Which of the following reactions would you expect to occur according to the activity series you established in part (a)? (1) \(2 \mathrm{~A}^{+}+\mathrm{D} \longrightarrow 2 \mathrm{~A}+\mathrm{D}^{2+}\) (2) \(\mathrm{D}^{2+}+2 \mathrm{C} \longrightarrow \mathrm{D}+2 \mathrm{C}^{+}\)

Short answer

Order: A > C > B > D. Reaction (2) will occur.

Step-by-step solution

Analyzing Reaction 1

The first reaction given is \(2 \mathrm{~A} + \mathrm{B}^{2+} \rightarrow 2 \mathrm{~A}^{+} + \mathrm{B}\). Here, \(\mathrm{A}\) reduces \(\mathrm{B}^{2+}\) to \(\mathrm{B}\), so \(\mathrm{A}\) is a stronger reducing agent than \(\mathrm{B}\).

Analyzing Reaction 2

The second reaction is \(\mathrm{B} + \mathrm{D}^{2+} \rightarrow \mathrm{B}^{2+} + \mathrm{D}\). Here, \(\mathrm{B}\) reduces \(\mathrm{D}^{2+}\) to \(\mathrm{D}\), so \(\mathrm{B}\) is a stronger reducing agent than \(\mathrm{D}\).

Analyzing Reaction 3

The third reaction \(\mathrm{A}^{+} + \mathrm{C} \rightarrow\) no reaction shows that \(\mathrm{C}\) is unable to reduce \(\mathrm{A}^{+}\) to \(\mathrm{A}\), indicating \(\mathrm{C}\) is a weaker reducing agent compared to \(\mathrm{A}\).

Analyzing Reaction 4

The fourth reaction is \(2 \mathrm{C} + \mathrm{B}^{2+} \rightarrow 2 \mathrm{C}^{+} + \mathrm{B}\). Here, \(\mathrm{C}\) reduces \(\mathrm{B}^{2+}\) to \(\mathrm{B}\), so \(\mathrm{C}\) is a stronger reducing agent than \(\mathrm{B}\).

Establishing the Order of Reducing Agents

From the previous steps, we have the following: \(\mathrm{A} > \mathrm{B}\) (from Step 1), \(\mathrm{B} > \mathrm{D}\) (from Step 2), and \(\mathrm{C} > \mathrm{B}\) (from Step 4). Additionally, \(\mathrm{A} > \mathrm{C}\) from Step 3. Combining these, the decreasing order of reducing ability is: \(\mathrm{A} > \mathrm{C} > \mathrm{B} > \mathrm{D}\).

Predicting Reaction Outcomes

With the order of reducing agents \(\mathrm{A} > \mathrm{C} > \mathrm{B} > \mathrm{D}\), let's assess the given reactions:1. \(2 \mathrm{~A}^{+} + \mathrm{D} \rightarrow 2 \mathrm{~A} + \mathrm{D}^{2+}\) - This reaction will not occur because \(\mathrm{D}\) is a weaker reducing agent than \(\mathrm{A}\).2. \(\mathrm{D}^{2+} + 2 \mathrm{C} \rightarrow \mathrm{D} + 2 \mathrm{C}^{+}\) - This reaction will occur because \(\mathrm{C}\) is a stronger reducing agent than \(\mathrm{D}\).

Key concepts

Activity Series

The activity series is a list of elements ranked by their ability to displace other elements in a compound, often observed through oxidation and reduction reactions. This series can be particularly useful in predicting how elements will behave during chemical reactions.

In an activity series, elements that can donate electrons easily and become oxidized are higher up in the series. These elements are considered strong reducing agents because they can reduce other substances by giving away electrons. For example, if we look at an activity series based on the reactions given, we see that element A has the highest reducing ability, meaning it is more easily oxidized than the other elements, which makes it a very strong reducing agent.

Understanding the positioning of elements in the activity series allows for easy prediction of which substances will undergo reactions more readily. In our exercise, we derived the order: A, C, B, D based on their reducing abilities. Such knowledge is instrumental in figuring out what kinds of reactions will occur when certain elements are mixed.

Chemical Reactions

Chemical reactions involve the breaking and forming of chemical bonds, leading to the transformation of substances. They can be of various types, but in the context of the activity series, we primarily look at redox reactions (oxidation-reduction reactions).

In redox reactions, a reducing agent (which loses electrons) transfers electrons to an oxidizing agent (which gains electrons). When element A reacts with B²⁺ to form A⁺ and B, A serves as the reducing agent. This indicates A's ability to supply electrons and thus its placement near the top of our activity series.

All chemical reactions must obey the law of conservation of mass and energy: the total mass and energy must remain constant throughout the reaction. This means that the number of atoms of each element is balanced on both sides of the reaction equation. By observing which elements take part as reducing agents and which are reduced itself, we can draw conclusions as to the relative strength of different reducing agents in the activity series.

Reaction Prediction

Reaction prediction involves determining the likelihood of certain chemical reactions happening based on the properties of the reactants. With the established order in the activity series, one can predict if a given reaction will proceed.

Let's refer to the activity order we established: A > C > B > D. With this ranking, we can anticipate that C can reduce both B²⁺ and D²⁺, while B can only reduce D²⁺, and D won't reduce any of the others effectively. This is because stronger reducing agents can donate their electrons more effectively, driving the reaction forward.

In reaction prediction, understanding the relative strength of reducing agents is key. For example, the reaction 2A⁺ + D will not proceed, as D cannot reduce A⁺ because A is superior in terms of reducing power. Conversely, D²⁺ + 2C proceeds because C is stronger than D as a reducing agent, making the transfer of electrons favorable.