Problem 84 - Chemistry and Chemical Reactivity

Question

Four metals, \(A, B, C,\) and \(D,\) exhibit the following properties: (a) Only A and C react with 1.0 M hydrochloric acid to give \(\mathrm{H}_{2}(\mathrm{g})\) (b) When \(\mathrm{C}\) is added to solutions of the ions of the other metals, metallic \(\mathbf{B}, \mathbf{D},\) and \(\mathbf{A}\) are formed. (c) 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 of increasing reducing ability is B, D, A, C.

Step 1: Understand Reactivity with HCl

Since only metals A and C react with 1.0 M HCl to release \( \mathrm{H}_{2}(\mathrm{g}) \), they are more reactive than hydrogen. B and D do not react with HCl, indicating they are less reactive than hydrogen.

Step 2: Analyze Reaction with Metal Ions

When C is added to solutions of the ions of other metals, it forms metallic A, B, and D. This indicates that C is more reactive than A, B, and D as it can displace the ions of all three metals from the solution.

Step 3: Examine Reduction Reaction of Metal D

Metal D reduces \( B^{n+} \) to metallic B and forms \( D^{n+} \). This implies D is a stronger reducing agent than B, as it can donate electrons to the \( B^{n+} \) ion, causing its reduction.

Step 4: Arrange the Metals Based on Reducing Ability

Considering all reactions, the order from least to greatest reducing ability is: B < D < A < C. B is the weakest reducing agent since D can reduce its ions, while C is the strongest as it displaces A, B, and D ions.

Key Concepts

Reducing Agents

Reducing agents are substances that donate electrons to other substances during chemical reactions. They help reduce the other substances by causing them to gain electrons. In other words, reducing agents become oxidized themselves.

• Consider the metal D in our example: it can reduce \( B^{n+} \) ions to metallic B by donating electrons. This makes D a reducing agent.
• The capability of a substance to act as a reducing agent depends on its tendency to donate electrons readily.
• Metals that more easily lose electrons, thereby oxidizing themselves while reducing other substances, are stronger reducing agents.

Different reducing agents have varying strengths based on their willingness to donate electrons. The stronger the tendency, the better the reducing agent. In the problem, metal C is the strongest because it can displace other metals from their ionic state.

Chemical Reactions

Chemical reactions involve rearrangements of atoms or ions to form different substances. When metals react with acids, such as hydrochloric acid, a typical displacement reaction may occur.

• For instance, when metals A and C react with hydrochloric acid, hydrogen gas is produced. This indicates that these metals are more reactive than hydrogen itself.
• Chemical reactions involving the donation of electrons often result in reduction and oxidation (redox reactions), such as when D reduces \( B^{n+} \) ions.
• Understanding which metals react in certain conditions helps categorize them in terms of reactivity.

These reactions are vital for identifying the order of reactivity and potential reducing strength of metals based on their interaction with other substances.

Metal Reactivity

Metal reactivity refers to the tendency of metals to participate in chemical reactions, often through losing electrons, which classifies them as reactive or less reactive. The series is based on their ability to displace hydrogen from acids or other metals from solutions.

• In the exercise, A and C show higher reactivity by reacting with hydrochloric acid, unlike B and D.
• C, being able to displace ions of A, B, and D when added to their solutions, showcases heightened reactivity compared to the others.
• The reactivity series helps predict which metals can replace others in chemical reactions.

Understanding metal reactivity is crucial for navigating displacement reactions and effectively organizing metals based on their reactivity levels.

Displacement Reactions

Displacement reactions are a type of chemical reaction where a more reactive metal can displace a less reactive one from its compound. These reactions highlight the competitive nature of metals.

• For example, metal C can displace A, B, and D from their ions, proving it as the most reactive among the four metals.
• These reactions provide insight into how easy it is for a metal to "win over" another's position in a compound.
• Using displacement reactions, it's possible to determine the order of reactivity and thereby arrange metals by their reducing power.

By observing which metals can displace others, predictions about their reactivity and placement within the reactivity series are made, aiding in understanding chemical behaviors.