Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Why Does the Colour of Copper Sulphate Solution Change When an Iron Nail is Dipped in It?


The interaction between copper sulphate solution and an iron nail is a fascinating chemical phenomenon that results in a distinct change in color. Understanding why this occurs requires an exploration of the underlying principles of chemical reactions and electron transfer. In this article, we will delve into the reasons behind the color change and shed light on the intricate chemistry at play.

The Chemistry of Copper Sulphate and Iron

To comprehend why the color of copper sulphate solution changes when an iron nail is dipped in it, we must first examine the nature of copper and iron ions. Copper sulphate, represented by the chemical formula CuSO4, is a compound that dissolves in water to form copper ions (Cu2+) and sulphate ions (SO42-). These ions are responsible for the blue color typically observed in copper sulphate solutions.

On the other hand, iron, represented by the symbol Fe, has the ability to undergo oxidation, a process where it loses electrons. When an iron nail is submerged in the copper sulphate solution, a redox reaction takes place, leading to the color change.

Redox Reaction and Electron Transfer

The color change observed in the copper sulphate solution is a result of a redox reaction, which involves both oxidation and reduction. During this process, electrons are transferred between the iron nail and the copper ions in the solution.

Oxidation of Iron

In the presence of copper sulphate, the iron nail undergoes oxidation. It loses electrons, leading to the formation of iron(II) ions (Fe2+). This oxidation process can be represented by the following equation:

Fe(s) → Fe2+(aq) + 2e-

Reduction of Copper

Simultaneously, the copper ions present in the solution undergo reduction. They gain electrons from the iron nail and are reduced to metallic copper, which has a distinct reddish-brown color. The reduction process can be represented by the equation:

Cu2+(aq) + 2e- → Cu(s)

The formation of metallic copper is responsible for the change in color observed in the solution. The previously blue solution now appears to have a reddish-brown hue due to the presence of finely dispersed copper particles.

Similar Question: An iron nail is dipped in the solution of copper sulphate for about 30 minutes. State the change in colour observed. Give reason for the change.

Frequently Asked Questions (FAQs)

FAQ 1: Why does the copper sulphate solution turn green after some time?

After some time, the copper sulphate solution may turn green due to the formation of basic copper carbonate. This occurs when carbon dioxide from the air reacts with the copper ions, resulting in the precipitation of greenish solid particles.

FAQ 2: Can other metals produce the same color change in copper sulphate solution?

The color change in copper sulphate solution is specific to the interaction with iron. Other metals may not produce the same effect because their chemical properties and reactivity differ from that of iron. The redox reaction and electron transfer that occur with iron are unique in causing the observed color change.

FAQ 3: Can the experiment be reversed by removing the iron nail from the solution?

Yes, the color change can be reversed by removing the iron nail from the copper sulphate solution. Once the iron nail is removed, the copper ions will no longer have a source of electrons for reduction. Over time, the solution will revert to its original blue color as the copper ions remain in their oxidized state.

FAQ 4: What happens if a rusted iron nail is used instead of a clean one?

If a rusted iron nail is used instead of a clean one, the rust will hinder the interaction between the iron and the copper sulphate solution. The rust layer acts as a barrier, preventing direct contact between the iron and the solution. As a result, the color change may not occur or may be less pronounced.

FAQ 5: Is the color change in copper sulphate solution a chemical or physical change?

The color change observed in the copper sulphate solution when an iron nail is dipped in it is a chemical change. It involves the formation of new substances (iron(II) ions and metallic copper) through a redox reaction. The change in color signifies the alteration in the chemical composition and properties of the solution.

FAQ 6: Are there any practical applications of this color change phenomenon?

The color change in copper sulphate solution due to the interaction with iron has practical applications in various fields. It can be used in educational settings to demonstrate redox reactions and electron transfer. Additionally, it serves as a visual indicator in certain chemical processes, helping scientists and researchers monitor the progress of reactions or the presence of specific substances.


The color change observed in copper sulphate solution when an iron nail is dipped in it is a result of a redox reaction between iron and copper ions. The iron nail undergoes oxidation, losing electrons and forming iron(II) ions, while the copper ions undergo reduction, gaining electrons and depositing metallic copper. This chemical transformation leads to the distinctive change in color, from blue to reddish-brown. By understanding the principles of redox reactions and electron transfer, we gain insights into the fascinating world of chemical interactions.

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