1 markVery Short AnswerSection A

What changes in the colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes ?

Q: What changes in the colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes ?

When iron nails are kept dipped in a blue copper sulphate ($CuSO_4$) solution for about 30 minutes, the following changes are observed: 1. The blue colour of the copper sulphate solution fades and turns into a light green colour due to the formation of iron(II) sulphate ($FeSO_4$) solution. 2. A brownish coating of copper metal is deposited on the surface of the iron nails. The chemical equation representing this displacement reaction is: $$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$$

Chemical Reactions and Equations

Displacement Reaction

Official Answer

When iron nails are kept dipped in a blue copper sulphate ( $CuSO_4$ ) solution for about 30 minutes, the following changes are observed:

The blue colour of the copper sulphate solution fades and turns into a light green colour due to the formation of iron(II) sulphate ( $FeSO_4$ ) solution.
A brownish coating of copper metal is deposited on the surface of the iron nails.

The chemical equation representing this displacement reaction is:

$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$

blue colour fadeslight greenbrownish depositdisplacement reactionFeSO4Cu

Marking Scheme

10.5 marks for mentioning that the blue colour of the solution fades or turns light green.
20.5 marks for mentioning that a brownish deposit of copper is formed on the iron nails.

Hint

Recall the reactivity series. A more reactive metal displaces a less reactive metal from its salt solution, leading to a change in colour of both the solution and the metal.

Quick Oral Answer

When iron is placed in copper sulphate solution, iron displaces copper because iron is more reactive than copper. The blue copper sulphate solution turns light green due to the formation of ferrous sulphate, and a brown layer of copper is deposited on the iron nail.

Analysis & Explanation

This reaction is a classic example of a displacement reaction. Iron ( $Fe$ ) is more reactive than copper ( $Cu$ ) according to the reactivity series. Therefore, iron displaces copper from its salt solution (copper sulphate). The copper ions ( $Cu^{2+}$ ) in the solution, which give it a characteristic blue colour, are reduced to metallic copper ( $Cu$ ) and deposit on the iron nail as a brown layer. Meanwhile, iron dissolves to form ferrous ions ( $Fe^{2+}$ ), which turn the solution light green.

Common Mistakes

1Writing that the nail turns green instead of the solution.
2Confusing the reaction as a double displacement reaction instead of a single displacement reaction.
3Not mentioning the time frame or the chemical names of the products formed.

Interesting Facts

This reaction is used in hydrometallurgy to extract copper from low-grade ores by displacing it with cheap scrap iron.

The green colour of the resulting ferrous sulphate solution is due to the presence of hydrated $Fe^{2+}$ ions.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2010?

This question carries 1 mark in the CBSE Class 10 Science 2010 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Displacement Reaction" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2010 paper?

This is a Very Short Answer question from Section A in the CBSE Class 10 Science 2010 paper.