Question 21 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+PbNO3⟶PbI+KNO3KI + PbNO_3 \longrightarrow PbI + KNO_3
(b)2KI+Pb(NO3)2⟶PbI2+2KNO32KI + Pb(NO_3)_2 \longrightarrow PbI_2 + 2KNO_3
(c)KI+Pb(NO3)2⟶PbI+KNO3KI + Pb(NO_3)_2 \longrightarrow PbI + KNO_3
(d)KI+PbNO3⟶PbI2+KNO3KI + PbNO_3 \longrightarrow PbI_2 + KNO_3

Official answer

The correct chemical equation is 2KI+Pb(NO3)2⟶PbI2+2KNO32KI + Pb(NO_3)_2 \longrightarrow PbI_2 + 2KNO_3.

Answer keywords:Lead nitratePotassium iodideLead iodideBalanced equationPb(NO3)2Pb(NO_3)_2KIKIPbI2PbI_2

Marking scheme

  1. 1.1 Mark for selecting the correct option (b) with the balanced chemical equation.

Hint

Recall the valency of Lead (Pb2+Pb^{2+}) and Nitrate (NO3−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.

Common mistakes

  1. 1.Writing the chemical formula of lead nitrate as PbNO3PbNO_3 instead of Pb(NO3)2Pb(NO_3)_2.
  2. 2.Forgetting to balance the potassium and iodide ions on both sides of the equation.

Analysis and explanation

In Activity 1.2, lead nitrate solution reacts with potassium iodide solution. Lead nitrate has the chemical formula Pb(NO3)2Pb(NO_3)_2 (since lead has a valency of +2+2 and nitrate has a valency of −1-1) and potassium iodide has the formula KIKI. When mixed, they undergo a double displacement reaction to form lead iodide (PbI2PbI_2), which is an insoluble yellow precipitate, and potassium nitrate (KNO3KNO_3). Balancing the chemical equation to satisfy the law of conservation of mass gives: 2KI(aq)+Pb(NO3)2(aq)⟶PbI2(s)+2KNO3(aq)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 PbNO3PbNO_3 for lead nitrate.
  • Option (c) is incorrect because it is unbalanced and uses the incorrect formula PbIPbI for lead iodide.

Interesting facts

The insoluble lead iodide (PbI2PbI_2) formed in this reaction is a bright yellow solid, often referred to as 'Golden Rain' when crystallized from hot water.

Question details

Q2 of 39 questions

Board
CBSE
Class
Class 10
Subject
Science
Year
2023
Section
Section A
Marks
1
Type
MCQ
Chapter
Chemical Reactions and Equations
Topic
Writing a Chemical Equation
Bloom's level
Applying
Syllabus topic
Chemical equations, balanced chemical equations, implications of a balanced chemical equation

Spotted a mistake or something unclear?

Tell us and we will fix it.

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.