Question

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

Short answer

(a) Order: A > B > C > D. (b) Neither reaction will occur.

Step-by-step solution

Analyze the Reactions for Element A

The first reaction is \( \mathrm{A} + \mathrm{B}^{+} \rightarrow \mathrm{A}^{+} + \mathrm{B} \). This implies that \( \mathrm{A} \) can reduce \( \mathrm{B}^{+} \) to \( \mathrm{B} \), meaning \( \mathrm{A} \) is a stronger reducing agent than \( \mathrm{B} \). So, \( \mathrm{A} > \mathrm{B} \) in reducing ability.

Establish Relationship Between B, C, and D

The reaction \( \mathrm{B} + \mathrm{D}^{+} \rightarrow \mathrm{B}^{+} + \mathrm{D} \) shows \( \mathrm{B} \) can reduce \( \mathrm{D}^{+} \). Another reaction, \( \mathrm{B} + \mathrm{C}^{+} \rightarrow \mathrm{B}^{+} + \mathrm{C} \), shows \( \mathrm{B} \) can also reduce \( \mathrm{C}^{+} \). Therefore, \( \mathrm{B} > \mathrm{D} \) and \( \mathrm{B} > \mathrm{C} \) in reducing ability.

Analyze the Absence of Reaction for D

The reaction \( \mathrm{C}^{+} + \mathrm{D} \rightarrow \text{no reaction} \) shows \( \mathrm{D} \) cannot reduce \( \mathrm{C}^{+} \). Hence, \( \mathrm{D} \) is a weaker reducing agent than \( \mathrm{C} \), i.e., \( \mathrm{D} < \mathrm{C} \).

Deduce the Overall Reducing Ability Order

From the analysis in previous steps, we can order the reducing capability as \( \mathrm{A} > \mathrm{B} > \mathrm{C} > \mathrm{D} \).

Predict Reaction (a) Outcome

The reaction \( \mathrm{A}^{+} + \mathrm{C} \rightarrow \mathrm{A} + \mathrm{C}^{+} \) can occur if \( \mathrm{C} \) is a stronger reducing agent than \( \mathrm{A} \). However, since \( \mathrm{A} > \mathrm{C} \), this reaction will not occur.

Predict Reaction (b) Outcome

The reaction \( \mathrm{A}^{+} + \mathrm{D} \rightarrow \mathrm{A} + \mathrm{D}^{+} \) can occur if \( \mathrm{D} \) can reduce \( \mathrm{A}^{+} \). Since \( \mathrm{A} > \mathrm{D} \), this reaction will also not occur.

Key concepts

Activity Series

The activity series is a useful tool for predicting whether certain chemical reactions will occur. It is essentially a list of elements organized by their ability to displace another element in a compound. The element higher on the list is a better reducing agent and more likely to lose electrons—making it more reactive. When determining the activity series for elements, we examine their reactions with each other. For example, if element A can displace element B from a compound, then A is higher on the activity series than B. This order helps in identifying which elements will react together and which will not. Understanding the activity series allows chemists to predict the outcome of chemical reactions, especially in redox processes where oxidation and reduction take place. It provides insight into the reactivity of metals, helping students and scientists make predictions without needing to conduct costly experiments.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, involve the transfer of electrons between two substances. In these reactions, one species undergoes oxidation (loses electrons), and another undergoes reduction (gains electrons). An easy way to remember this is through the acronym OIL RIG: Oxidation Is Loss, Reduction Is Gain. In the context of the given equation, where A, B, C, and D are considered: - A reducing agent is something that donates electrons. - It helps another substance gain electrons and become reduced. - Simultaneously, the reducing agent itself becomes oxidized. The strength of reducing agents can be evaluated through experimental observation of their behavior in reactions—exactly what was done in the reactions discussed earlier. This forms the basis for establishing an activity series ranking among the elements.

Chemical Reactivity

Chemical reactivity refers to how readily a substance undergoes a chemical change. It is influenced by both the nature of the substance and what it interacts with. Highly reactive substances tend to form new bonds quickly and release more energy during a reaction. In the context of metal reactivity, those that are higher on the activity series are more reactive. Reactivity is important across chemistry because it determines the conditions under which reactions occur and the products formed: - Metals high on the activity series displace those lower on the list in compounds. - This ability is rooted in their electron configuration and the ease with which they donate electrons. By mastering the concept of chemical reactivity, students can better understand and predict how various chemicals will behave when mixed. This is important for both laboratory scenarios and industrial applications.

Reaction Prediction

Predicting chemical reactions involves determining whether a reaction will take place based on known principles, such as the activity series or the reactivity of the elements involved. To predict a reaction, you typically need to:- Analyze the potential reactants and products.- Use the activity series to compare the reducing ability of metals involved.- Assess the likelihood of one substance displacing another.In the exercise, predictions were made about the reactions like \( A^{+} + C \rightarrow A + C^{+} \) based on the established activity series \( \text{A} > \text{B} > \text{C} > \text{D} \). Since A is a stronger reducing agent compared to C, the forward reaction will not occur.By integrating these concepts, students can predict whether a reaction will proceed and verify their predictions experientially or through theoretical understanding.