Problem 96 - Chemistry and Chemical Reactivity

Question

A Four metals, \(A, B, C,\) and \(D,\) exhibit the following properties: (i) Only \(\mathrm{A}\) and \(\mathrm{C}\) react with \(1.0 \mathrm{M}\) hydrochloric acid to give \(\mathrm{H}_{2}(\mathrm{g})\) (ii) When \(\mathrm{C}\) is added to solutions of the ions of the other metals, metallic \(\mathrm{B}, \mathrm{D},\) and \(\mathrm{A}\) are formed. (iii) Metal D reduces \(B^{n+}\) to give metallic \(B\) and \(D^{n+}\) Based on this information, arrange the four metals in order of increasing ability to act as reducing agents.

Step-by-Step Solution

Answer

The order is B, A, D, C.

Step 1: Understanding the Reactivity with Acid

From property (i), only metals A and C react with hydrochloric acid, indicating that these metals can displace hydrogen from the acid. This suggests A and C are more reactive than B and D regarding hydrogen gas evolution.

Step 2: Analyzing the Reaction with Metal Ions

Property (ii) tells us that when C is added to solutions containing ions of other metals, it forms metallic B, D, and A. This means that metal C is more reactive than metals A, B, and D in these displacement reactions.

Step 3: Interpreting Metal D's Reducing Ability

Property (iii) indicates that metal D can reduce B ions to form metallic B while D is oxidized to D ions. This suggests D is a stronger reducing agent than B.

Step 4: Drawing Conclusions Based on All Observations

- From step 1, we know A and C are more reactive than B and D. - From step 2, C is more reactive than A, B, and D. - From step 3, D is a stronger reducing agent than B. - Therefore, the order of increasing ability to act as reducing agents is: B, A, D, C.

Key Concepts

Reducing Agents

Reducing agents are substances that donate electrons in a chemical reaction. They help other substances get reduced by giving away electrons, while themselves becoming oxidized. This concept is crucial in redox reactions (reduction-oxidation reactions). In the exercise, we identify metals that act as reducing agents by looking at how they interact with other metal ions.
In the scenario provided, metal D reduces the ions of metal B, transforming them into metallic B. During this process, D gives away electrons to B, showing its capability as a reducing agent. When D turns into its ionic form ( +), it indicates its involvement in a redox reaction where it donates electrons. By understanding this, we conclude that D acts more strongly as a reducing agent compared to B because it is able to donate electrons more effectively.

Displacement Reactions

Displacement reactions involve a more reactive metal displacing a less reactive metal from its ionic compound. This type of reaction can help us determine the relative reactivity of different metals.
In the problem, when metal C is added to solutions of metal ions of A, B, and D, it results in the formation of metallic A, B, and D. This shows that C is the most reactive among these metals because it can displace other metals from their ionic states. Displacement reactions are a clear way to illustrate metal reactivity. Reactivity series often use such displacement reactions to help predict how metals will behave in chemical reactions, making the prediction and comparison of their reactivity straightforward.

Reactivity with Acids

Reactivity with acids is another important indicator of metal reactivity. When a metal is able to react with an acid like hydrochloric acid (HCl), it usually releases hydrogen gas ( H_2(g)). This property is useful to gauge how reactive a metal is towards acids.
In the exercise, metals A and C can react with 1.0 M hydrochloric acid to release hydrogen gas. This reaction suggests that A and C are more reactive than B and D in terms of acid reactivity. It is a basic principle that only metals more reactive than hydrogen in the reactivity series can displace hydrogen in such reactions. This specific ability to react with acids, by evolution of hydrogen, confirms the relative positions of these metals in terms of their reactivity.