Problem 108 - Chemistry and Chemical Reactivity

Question

A Four metals, \(A, B, C,\) and \(D\), exhibit the following properties: (a) Only A and C react with L.O M hydrochloric acid to give \(\mathrm{H}_{2}(\mathrm{g})\) (b) When \(C\) is added to solutions of the ions of the other metals, metallic \(\mathrm{B}, \mathrm{D},\) and \(\mathrm{A}\) are formed. (c) Metal D reduces \(\mathrm{B}^{n+}\) to give metallic \(\mathrm{B}\) and \(\mathbf{D}^{n+1}\) 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: Analyze Reactivity with Hydrochloric Acid

Metal A and C react with hydrochloric acid, indicating that both have the capability to reduce hydrogen ions to hydrogen gas. Metals B and D do not react with hydrochloric acid, making them weaker reducing agents than A and C in this context.

Step 2: Determine Reactivity of Metal C with Other Metal Ions

Metal C can displace metals B, D, and A from their ionic solutions, suggesting that C is a better reducing agent than B, D, and A. This means C must be lower on the reducing agent scale compared to A, since C can displace A.

Step 3: Examine Metal D's Reaction with Metal B

Metal D can reduce B ions to metallic B, showing that D is a stronger reducing agent than B. However, Metal D cannot displace Metal C from its compounds since there's no reaction stated that involves D displacing C.

Step 4: Arrange the Metals by Reducing Ability

Since C can react with ions of all the other metals, it is the strongest reducing agent. Since D can reduce B ions to metallic B but not displace C, D is the next strongest reducing agent. Finally, since A reacts with hydrochloric acid while B does not, A is a stronger reducing agent than B. Therefore, the order from weakest to strongest reducing agent is B, A, D, C.

Key Concepts

Metals Reactivity

When we talk about metals reactivity, we are discussing how metals interact with other substances, particularly how they engage in reactions. A metal's reactivity can be gauged by its ability to lose electrons, which allows it to form positive ions. This capability often determines whether a metal can react with common substances like water or acids. Some metals react vigorously, while others do not react at all.

Consider metals reacting with hydrochloric acid—a commonly used acid in chemistry. More reactive metals will easily lose electrons to reduce hydrogen ions, resulting in the formation of hydrogen gas. Less reactive metals either react slowly or not at all. Metals like potassium and sodium reach the top of the reactivity series due to their eagerness to part with their electrons.

Reducing Agents

Reducing agents are substances that donate electrons during a chemical reaction. In doing so, they cause the reduction of another substance while they themselves become oxidized. Metals often act as reducing agents because of their tendency to lose electrons.

The strength of a reducing agent is determined by its ability to give away electrons. Metals that easily lose electrons and oxidize readily make strong reducing agents. For instance, in the exercise, when metal C displaces other metals from their solutions, it exhibits strong reducing properties by readily donating electrons. On the other hand, a metal that doesn’t easily relinquish its electrons, like metal B in the provided example, would be a weaker reducing agent.

Hydrochloric Acid Reaction

The hydrochloric acid reaction with metals is a classic example used to teach basic chemistry concepts. When a metal reacts with hydrochloric acid (HCl), it can produce hydrogen gas if the metal is reactive enough. This indicates that the metal is capable of reducing the hydrogen ions from the acid.

For example, if metal A reacts with dilute hydrochloric acid and produces hydrogen gas, it confirms the metal's reactivity and its ability to serve as a reducing agent to some degree. Hence, metals A and C, which reacted with HCl in the exercise, have stronger reducing tendencies compared to metals B and D, which did not react.

Displacement Reaction

A displacement reaction occurs when a more reactive element displaces a less reactive element from its compound. In metals, this often involves a more reactive metal displacing a less reactive metal from a solution of its ions.

In the exercise's context, metal C displaces metals B, D, and A from their ionic solutions. This confirms that metal C is more reactive than the others and a strong reducing agent. Displacement reactions not only highlight differences in reactivity among metals but also offer insight into their positions in the reactivity series. The element that can displace another from its compound is always the one higher up in this series.