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 (Ag) does not react with copper sulphate solution.

Step 1: Understanding the Reaction

When a metal is placed in a solution of another metal cation, a reaction will occur if the displacing metal is more reactive (higher in the reactivity series) than the metal ion dissolved in the solution. The more reactive metal will displace the less reactive one from the solution.

Step 2: Identify the Reactivity Series

The reactivity series lists metals in order of decreasing reactivity. Important positions include: magnesium (Mg), zinc (Zn), iron (Fe) above copper (Cu), and silver (Ag) below copper. This order helps predict reaction outcomes.

Step 3: Analyzing Each Metal

Let's consider each option: - (a) Fe: Iron is above copper in the reactivity series, so it will displace copper from copper sulphate. - (b) Zn: Zinc is also above copper, thus can displace copper. - (c) Ag: Silver is below copper and cannot displace copper from copper sulphate. - (d) Mg: Magnesium is above copper, so it can displace copper.

Step 4: Selecting the Correct Answer

Since silver (Ag) is below copper in the reactivity series, it does not have the ability to displace copper from the copper sulphate solution.

Key Concepts

Displacement Reactions

Displacement reactions are fascinating chemical processes where a more reactive metal displaces a less reactive metal from its compound. Imagine it like a dance where a stronger partner cuts in and takes over. In displacement reactions, the strength or reactivity of the metals determines the outcome. These reactions typically involve metals and their solutions. When a single element replaces another in a compound, it’s due to its position in the reactivity series. In simpler terms, if the metal is higher up in the reactivity series, it can "push" out a metal that is lower in the series from its compound. For example:

• If you place zinc in a copper sulphate solution, zinc will displace copper, forming zinc sulfate and freeing copper.
• Reactivity order is key: the more reactive metal pushes out the less reactive one.

Understanding these processes is essential for predicting how different metals will behave in a reaction.

Copper Sulfate Reactions

Copper sulfate reactions are a great way to observe displacement reactions. Copper sulfate (\( ext{CuSO}_4 \)) is a blue solution that can visually show these chemical changes.When a metal more reactive than copper comes into contact with copper sulfate:

• The solution might change color, indicating a chemical change.
• The metal often gets covered with a layer of copper, showing copper being displaced.

These visible changes make \( ext{CuSO}_4 \) reactions fantastic for experiments and learning. Watching these transformations helps understand which metals are more reactive and why positioning in the reactivity series matters.

Reactivity of Metals

The reactivity of metals is an important concept in chemistry that ranks metals based on their ability to displace others in compounds. This "ranking" is called the reactivity series, and it explains why certain metals are more likely to engage in displacement reactions. Here's how it works:

• Metals such as magnesium (Mg), zinc (Zn), and iron (Fe) are highly reactive and can displace copper (Cu) from its solutions.
• Metals like silver (Ag), which are lower in the reactivity series than copper, cannot displace it.

The position in the reactivity series provides a quick snapshot of a metal's displacement power. This hierarchy helps predict outcomes when metals encounter solutions of different metallic ions in various chemical mixes.