Problem 68 - A Complete Resource Book in Chemistry for JEE Main

Question

Zinc-copper couple that can be used as a reducing agent is obtained by (a) zinc coated with copper (b) zinc and copper wires welded together (c) mixing zinc dust and copper gauze (d) copper coated with zinc

Step-by-Step Solution

Answer

The answer is (d) copper coated with zinc.

Step 1: Understanding the Question

The problem asks us to identify how a zinc-copper couple, which serves as a reducing agent, is formed among the options given. We must consider how each option facilitates the creation of a useful reducing agent.

Step 2: Examining Option A: Zinc Coated with Copper

Consider a scenario where zinc is covered with copper. This option may not allow effective interaction as the copper coat can reduce zinc's surface available for reaction, potentially inhibiting its reducing ability.

Step 3: Examining Option B: Zinc and Copper Wires Welded Together

This configuration would involve physically joining two metals, which theoretically could work, but might not maximize the area where the metals interact, which is crucial for reduction reactions.

Step 4: Examining Option C: Mixing Zinc Dust and Copper Gauze

In this option, zinc and copper are in forms that maximize their surface areas (zinc dust and copper gauze). This creates a large number of contact points for interactions, enhancing the reducing capability.

Step 5: Examining Option D: Copper Coated with Zinc

Here, the outer zinc layer can engage directly in reactions as a reducing agent, with copper potentially facilitating electron transfer. This setup can indeed form a zinc-copper couple known for its reducing properties.

Step 6: Selecting the Best Option

After examining all options, Option D (Copper coated with zinc) is most known for effectively creating a zinc-copper couple, as zinc's high reactivity is harnessed on the outer surface of the coating.

Key Concepts

Reducing Agents

Reducing agents play a significant role in chemical reactions by donating electrons to other substances. This donation process reduces the other substance, meaning it gains electrons and often decreases in oxidation state. Reducing agents themselves become oxidized in the process. In other words, they lose electrons.

A good reducing agent is one that easily gives up electrons. Some factors to consider are:

• Electron Availability: Metals that are electropositive, like zinc, readily give electrons.
• Surface Area: Greater surface area allows more interactions, enhancing reducing efficiency.
• Reactivity: Highly reactive metals often serve as more effective reducing agents.

Using zinc and copper together, specifically in a zinc-coated format, creates an effective reducing environment as zinc loses electrons readily to facilitate reduction.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, also known as redox reactions, involve the transfer of electrons between entities. They play a crucial role in both chemistry and biology.

In a redox reaction:

• Oxidation is the process where a substance loses electrons, resulting in an increase in oxidation state.
• Reduction is the gain of electrons by a substance, resulting in a decrease in oxidation state.

The zinc-copper couple engages in redox reactions by facilitating the electron transfer from zinc to copper. Here, zinc serves as an excellent reducing agent due to its natural tendency to donate electrons, while copper often assists in the electron transfer process. This interaction effectively drives many industrial and organic reactions.

Metal Surface Interactions

The interaction between different metal surfaces can significantly impact the efficiency of chemical processes like reducing reactions.

When metals such as zinc and copper are in contact, their surface interaction is key to the reaction's success. Here are some considerations of how surface interactions aid reactions:

• Surface Contact Points: Increased contact points between metals allow more opportunities for electron exchange.
• Coating Effects: Coating one metal with another, for instance layering copper over zinc, helps create a specialized surface that is more interactive.
• Particle Size: Smaller particles, such as zinc dust, have a higher surface area, enabling more thorough chemical interactions.

The strategic interaction of metal surfaces enhances the role of reducing agents like a zinc-copper couple, providing a controlled environment for efficient reduction reactions.