Problem 12 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

What will occur if a block of copper metal is dropped into a beaker containing a solution of \(1 \mathrm{M} \mathrm{ZnSO}_{4}\) ? [Main Online April 9, 2016] (a) The copper metal will dissolve with evolution of oxygen gas (b) The copper metal will dissolve with evolution of hydrogen gas (c) No reaction will occur (d) The copper metal will dissolve and zinc metal will be deposited.

Step-by-Step Solution

Answer

(c) No reaction will occur.

Step 1: Identify Metal Activity Series

In the electrochemical series (or activity series of metals), the ability of a metal to displace another from a solution is determined by their relative reactivities. Zinc is more reactive than copper, meaning zinc can displace copper from its compound, but not vice versa.

Step 2: Analyze the Reaction Possibility

Since copper is less reactive than zinc, it cannot displace zinc ions from the solution. Therefore, no redox reaction will occur between copper and the zinc sulfate solution.

Step 3: Conclusion and Answer Selection

Given that copper cannot displace zinc, option (c) "No reaction will occur" is the most accurate description of what will happen when copper is placed in a zinc sulfate solution.

Key Concepts

Copper and Zinc Reaction

When we explore the reaction possibilities between copper and zinc, it's essential to consider their reactivities. Suppose you have a scenario where a copper block is introduced into a zinc sulfate solution. You might wonder if they will chemically react. This setup is a classic example to discuss because copper and zinc frequently interact in various metallurgical processes.

Copper, being less reactive than zinc, does not have the ability to displace zinc from its zinc sulfate compound. In simple terms, copper can't push away zinc ions from the solution to form copper sulfate. This is a fundamental principle observed in displacement reactions where only the more reactive metal can replace the less reactive metal from its compound. Thus, in this case, copper will not react with zinc sulfate, and no observable changes or chemical reactions will occur. It's straightforward: since copper lacks the necessary reactivity compared to zinc, it simply stays unchanged in the solution.

Electrochemical Series

The Electrochemical Series is a list of elements ordered by their standard electrode potentials. This sequence helps us understand which metals can displace others in a solution, providing a clear map of metal reactivity. Within this series, zinc is placed ahead of copper, indicating its higher reactivity.

Standard electrode potentials, which are measured under standard conditions, reveal a metal's tendency to lose electrons (oxidation) or gain electrons (reduction). More reactive metals appear at the top with higher oxidation tendencies, and less reactive metals like copper are found towards the bottom.

In our scenario, the Electrochemical Series tells us that zinc, which comes with a more negative electrode potential, can easily lose electrons compared to copper. Thus, if you try to drop a copper block in a zinc sulfate solution, no displacement reaction occurs, because copper can't reduce zinc ions due to its lower position on the series.

Redox Reaction Analysis

Redox reactions, short for reduction-oxidation reactions, involve the transfer of electrons between two substances. These reactions are pivotal because they encompass processes where one element is oxidized and another is reduced. However, not every combination of metals and solutions will result in a redox reaction.

In the case of copper and zinc sulfate solution, we analyze whether a redox reaction is feasible. A redox reaction occurs if the metal in the solution can be displaced by a more reactive metal. Since copper cannot donate electrons to zinc ions in the solution, no transfer of electrons occurs. Thus, no redox reaction takes place.

This analysis emphasizes the rule that for a redox reaction to occur, a more reactive metal must be present to initiate electron transfer. Without this necessary reactivity, as shown in the copper and zinc sulfate example, the substances remain unchanged, and no redox transformation is observed.