1 markMCQSection A

When aqueous solutions of potassium iodide and lead nitrate are mixed, an insoluble substance separates out. The chemical equation for the reaction involved is :

Chemical Reactions and Equations

Writing a Chemical Equation

Options

(a)

KI + PbNO_3 \longrightarrow PbI + KNO_3

(b)

2KI + Pb(NO_3)_2 \longrightarrow PbI_2 + 2KNO_3

(c)

KI + Pb(NO_3)_2 \longrightarrow PbI + KNO_3

(d)

KI + PbNO_3 \longrightarrow PbI_2 + KNO_3

Official Answer

The correct chemical equation is $2KI + Pb(NO_3)_2 \longrightarrow PbI_2 + 2KNO_3$ .

Lead nitratePotassium iodideLead iodideBalanced equation

Pb(NO_3)_2

KI

PbI_2

Marking Scheme

11 Mark for selecting the correct option (b) with the balanced chemical equation.

Hint

Recall the valency of Lead ( $Pb^{2+}$ ) and Nitrate ( $NO_3^-$ ) to write the correct formula for lead nitrate, and then balance the atoms on both sides.

Quick Oral Answer

When potassium iodide reacts with lead nitrate, a yellow precipitate of lead iodide is formed along with potassium nitrate solution.

Analysis & Explanation

In Activity 1.2, lead nitrate solution reacts with potassium iodide solution. Lead nitrate has the chemical formula $Pb(NO_3)_2$ (since lead has a valency of $+2$ and nitrate has a valency of $-1$ ) and potassium iodide has the formula $KI$ . When mixed, they undergo a double displacement reaction to form lead iodide ( $PbI_2$ ), which is an insoluble yellow precipitate, and potassium nitrate ( $KNO_3$ ). Balancing the chemical equation to satisfy the law of conservation of mass gives: $2KI(aq) + Pb(NO_3)_2(aq) \longrightarrow PbI_2(s) + 2KNO_3(aq)$ .

Option (a) and (d) are incorrect because they use the incorrect chemical formula $PbNO_3$ for lead nitrate.
Option (c) is incorrect because it is unbalanced and uses the incorrect formula $PbI$ for lead iodide.

Common Mistakes

1Writing the chemical formula of lead nitrate as $PbNO_3$ instead of $Pb(NO_3)_2$ .
2Forgetting to balance the potassium and iodide ions on both sides of the equation.

Interesting Facts

The insoluble lead iodide ( $PbI_2$ ) formed in this reaction is a bright yellow solid, often referred to as 'Golden Rain' when crystallized from hot water.

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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 "Writing a Chemical Equation" 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.