Question

Based on the following information arrange four metals, \(A, B, C\) and \(D\) in order of increasing ability to act as reducing agents : (I) Only \(C\) react with \(1 M \mathrm{HCl}\) to give \(\mathrm{H}_{2}(g)\) (II) When \(A\) is added to solution of the other metal ions, metallic \(D\) is formed but not \(B\) or \(C\) (a) \(D

Short answer

The correct order of increasing ability to act as reducing agents is: (a) D<A<C<B.

Step-by-step solution

Examining Reactivity with HCl

The ability of a metal to act as a reducing agent can be determined by its reactivity with acids. Since only 'C' reacts with 1 M HCl to give hydrogen gas, it suggests that metal 'C' is reactive enough to displace hydrogen from the acid, implying it is a relatively good reducing agent.

Analyzing A's Reaction with Metal Ions

When metal 'A' is added to the solutions of the other metal ions, metallic 'D' is formed, while 'B' and 'C' are not. This indicates that 'A' can reduce the ions of 'D' back to metallic 'D', therefore 'A' must be a better reducing agent than 'D'. Because no reaction takes place with 'B' or 'C', 'A' must be a less effective reducing agent than 'B' and 'C'.

Determining the Order

Based on the information given, 'C' can act as a reducing agent with HCl, and 'A' can reduce 'D' but not 'B' or 'C'. This implies that 'C' is a better reducing agent than 'A', which is in turn a better reducing agent than 'D'. Metal 'B' does not react, thus it's either the least reactive or most reactive. Since 'C' is known to react with HCl and 'A' does not produce metallic 'B', it is inferred that 'B' is the least reactive and worst reducing agent, giving us the final order: 'D < A < C < B'.

Key concepts

Reducing Agents

Reducing agents are substances that donate electrons to other materials during chemical reactions, effectively reducing them. The 'reduction' here refers to the decrease in oxidation state by gaining electrons. In the context of our metals exercise, when we refer to a metal acting as a reducing agent, we're focusing on its ability to transfer electrons to hydrogen ions from the acid to form hydrogen gas.

From our step by step solution, we know that metal 'C' was able to react with hydrochloric acid to produce hydrogen gas, which means that 'C' successfully donated electrons and acted as a reducing agent. The ease with which a metal can donate electrons (and thus act as a reducing agent) is greatly influenced by its position in the electrochemical series. Metals that are higher in the series, such as alkali metals, are more likely to act as strong reducing agents. Understanding how to identify a good reducing agent is key to solving problems involving redox reactions and predicting the outcome of chemical reactions.

Chemical Reactivity

Chemical reactivity, in general, is the ability of a substance to undergo chemical changes or reactions. For metals, this often means losing electrons to form ions. This concept is directly related to the behavior of reducing agents, as more reactive metals will more readily lose electrons and act as better reducing agents.

The exercise showed us that some metals react differently when placed in various environments. For instance, Metal 'C' reacted with \(1 M \mathrm{HCl}\) to produce \(\mathrm{H}_{2}(g)\), indicating a higher chemical reactivity relative to the other metals in question. Metal 'A', while capable of reducing metal 'D' to its elemental form, could not do the same with 'B' or 'C', which tells us about the reactivity hierarchy among these metals. Determining chemical reactivity is essential when predicting reaction outcomes, understanding the feasibility of certain reactions, and even in practical applications like corrosion prevention.

Metal Reactivity Order

The concept of metal reactivity order is fundamental to understanding how various metals will behave in a chemical reaction. This order is usually determined by looking at the activity series of metals, which ranks them based on their ability to displace hydrogen from acids or to displace other metals from solutions.

In the given exercise, we are tasked to order metals based on their ability to act as reducing agents. The reactivity series implies that the most reactive metal will react with a wide range of substances, including dilute acids, to form a corresponding salt and hydrogen. As we concluded from our solution, the order of metal reactivity as reducing agents for 'A', 'B', 'C', and 'D', is 'D < A < C < B', which means 'B' is the least reactive as a reducing agent and 'C' being the most reactive. Students should remember that the metal reactivity order can be counterintuitive; it is not necessarily aligned with intuition but is based on empirical observations and the activity series.