Assertion (A): The colour of aqueous solution of copper sulphate turns colourless when a piece of lead is added to it.

Reason (R): Lead is more reactive than copper, and hence displaces copper from its salt solution.

Chemical Reactions and Equations

Displacement Reaction

Options

(a)Both (A) and (R) are true and (R) is the correct explanation of (A).

(b)Both (A) and (R) are true, but (R) is not the correct explanation of (A).

(c)(A) is true, but (R) is false.

(d)(A) is false, but (R) is true.

Official Answer

The correct option is (a). Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).

displacement reactionreactivity seriescopper sulphatelead sulphatecolourless

Marking Scheme

11 Mark: Correct option (a) selected with accurate explanation of the displacement reaction and reactivity.

Hint

Think about the reactivity series. Is lead ( $Pb$ ) placed above or below copper ( $Cu$ )? What happens to the blue copper sulphate solution when a more reactive metal displaces copper?

Quick Oral Answer

Lead is more reactive than copper, so it displaces copper from copper sulphate solution to form lead sulphate and copper. Since lead sulphate is insoluble and white, the blue colour of the solution disappears.

Analysis & Explanation

Assertion (A) states that the blue colour of an aqueous solution of copper sulphate turns colourless when a piece of lead is added to it. This is true because lead ( $Pb$ ) is more reactive than copper ( $Cu$ ). When lead is added to a copper sulphate ( $CuSO_4$ ) solution, it displaces copper to form lead sulphate ( $PbSO_4$ ) and copper metal:

$Pb(s) + CuSO_4(aq) \rightarrow PbSO_4(s) + Cu(s)$

Since lead sulphate ( $PbSO_4$ ) is an insoluble white precipitate, the blue colour of the copper sulphate solution fades away, leaving a colourless supernatant liquid.

Reason (R) states that lead is more reactive than copper and hence displaces copper from its salt solution. This is also true and directly explains why the displacement reaction occurs, causing the blue copper sulphate solution to lose its colour. Therefore, (R) is the correct explanation of (A).

Common Mistakes

1Thinking that lead is less reactive than copper because it is a heavy metal.
2Not realizing that lead sulphate is insoluble and forms a white precipitate, which makes the solution lose its blue colour and become colourless.

Interesting Facts

Lead is placed above hydrogen and copper in the reactivity series, making it reactive enough to displace copper from its salt solutions, even though it reacts very slowly with acids due to the formation of protective insoluble coatings.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2023?

This question carries 1 mark in the CBSE Class 10 Science 2023 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 2023 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2023 paper.