Problem 39 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following metal does not react with the solution of copper sulphate? (a) \(\mathrm{Fe}\) (b) \(\mathrm{Zn}\) (c) \(\mathrm{Ag}\) (d) \(\mathrm{Mg}\)

Step-by-Step Solution

Answer

Silver ( ext{Ag}) does not react with copper sulphate.

Step 1: Identify the Reaction

Copper sulphate ( ext{CuSO}_4) can react with metals through a single displacement reaction if the metal is more reactive than copper. In such reactions, the more reactive metal displaces copper from copper sulphate solution.

Step 2: Activity Series Consultation

Refer to the activity series of metals, which is a list of metals ranked according to their reactivity. In this series, a metal can displace another metal from a compound only if it is placed higher in the series.

Step 3: Locate Metals on the Activity Series

Check the position of iron ( ext{Fe}), zinc ( ext{Zn}), silver ( ext{Ag}), and magnesium ( ext{Mg}) relative to copper ( ext{Cu}) in the activity series. Iron, zinc, and magnesium are placed above copper, indicating they are more reactive than copper.

Step 4: Identify the Metal Below Copper

Silver ( ext{Ag}) is below copper in the activity series, indicating it is less reactive and cannot displace copper from copper sulphate. Consequently, it will not react.

Step 5: Select Non-Reactive Metal

Determine which metal from the list (a) ext{Fe}, (b) ext{Zn}, (c) ext{Ag}, (d) ext{Mg} does not react with ext{CuSO}_4 based on its position in the activity series. From previous analysis, silver ( ext{Ag}) does not react.

Key Concepts

Single Displacement Reaction

A single displacement reaction is a type of chemical reaction where a more reactive metal displaces a less reactive metal in a compound. These reactions are pretty straightforward to recognize and follow a simple pattern: \( A + BC \rightarrow AC + B \). Here, \( A \) is the more reactive metal and \( BC \) is a compound containing a less reactive metal, \( B \). As a result, \( A \) replaces \( B \) forming a new compound, \( AC \), while \( B \) is released as a free element.

For a displacement to occur, the metal attempting to displace another must be higher in the reactivity series. If it is not, no reaction will take place. This type of reaction not only highlights differences in metal reactivities but also is pivotal in industries such as metallurgy, where they are used to extract metals from their ores.

To quickly identify whether a single displacement reaction can occur, always refer to the metal reactivity series—a handy chart listing metals by their reaction tendencies.

Copper Sulphate Reaction

Copper sulfate, with the chemical formula \( \mathrm{CuSO}_4 \), is often involved in single displacement reactions. When reacting with a more reactive metal, the copper ions are reduced and precipitate as metallic copper, while the other metal ions go into solution.

Consider \( \mathrm{CuSO}_4 \) reacting with zinc, \( \mathrm{Zn} \): the chemical equation can be written as

\[ \mathrm{Zn} + \mathrm{CuSO}_4 \rightarrow \mathrm{ZnSO}_4 + \mathrm{Cu} \]

Here, zinc displaces copper from its sulfate compound, forming \( \mathrm{ZnSO}_4 \), while copper is deposited as a solid. This process results in the distinctive blue color of the copper sulfate solution fading as copper exits the solution, signaling that a reaction has occurred.

When you conduct such a reaction in a lab setting, it is easily observable due to the solid copper forming. This experiment is not only fascinating visually but is also perfect for understanding the principles of reactivity.

Metal Reactivity Series

The metal reactivity series is a germane tool in chemistry that ranks metals by their reactivity from highest to lowest. Metals higher up can displace those lower in the series from their compounds. This list becomes a guide to predict the outcomes of reactions between metals and compounds.

For example, when considering reaction possibilities with copper sulfate (\( \mathrm{CuSO}_4 \)), one would look at the metals iron (\( \mathrm{Fe} \)), zinc (\( \mathrm{Zn} \)), silver (\( \mathrm{Ag} \)), and magnesium (\( \mathrm{Mg} \)). In the metal reactivity series:

• Iron, zinc, and magnesium are above copper.
• Silver is below copper.

This tells us that iron, zinc, and magnesium are reactive enough to displace copper from its compound, but silver is not. Such insights allow chemists to predict and confirm reactions, ensuring that experimental outcomes in labs and industries wrap in alignment with theoretical predictions.