Q6
3 marksShort AnswerSection C

2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction.

Chemical Reactions and Equations
Types of Chemical Reactions
Official Answer

(a) Zinc reacting with silver nitrate:

  • Type of Reaction: Displacement Reaction (Zinc is more reactive than silver and displaces silver from its nitrate solution).
  • Balanced Chemical Equation:

Zn(s)+2AgNO3(aq)Zn(NO3)2(aq)+2Ag(s)Zn(s) + 2AgNO_3(aq) \rightarrow Zn(NO_3)_2(aq) + 2Ag(s)


(b) Potassium iodide reacting with lead nitrate:

  • Type of Reaction: Double Displacement Reaction (or Precipitation Reaction, as a yellow precipitate of lead iodide is formed by the exchange of ions).
  • Balanced Chemical Equation:

Pb(NO3)2(aq)+2KI(aq)PbI2(s)+2KNO3(aq)Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) + 2KNO_3(aq)

displacement reactiondouble displacementprecipitationZn + 2AgNO3Pb(NO3)2 + 2KI

Marking Scheme

  • 1Identify (a) as a displacement reaction (0.5 marks)
  • 2Write balanced equation for (a): Zn(s)+2AgNO3(aq)Zn(NO3)2(aq)+2Ag(s)Zn(s) + 2AgNO_3(aq) \rightarrow Zn(NO_3)_2(aq) + 2Ag(s) (1 mark)
  • 3Identify (b) as a double displacement / precipitation reaction (0.5 marks)
  • 4Write balanced equation for (b): Pb(NO3)2(aq)+2KI(aq)PbI2(s)+2KNO3(aq)Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) + 2KNO_3(aq) (1 mark)

Hint

For (a), compare the reactivity of zinc and silver. For (b), think about the exchange of ions between lead nitrate and potassium iodide as seen in Activity 1.2.

Quick Oral Answer

Zinc displaces silver because it is more reactive, representing a displacement reaction. Lead nitrate and potassium iodide exchange ions to form a yellow precipitate of lead iodide, representing a double displacement reaction.

Analysis & Explanation

In part (a), zinc (ZnZn) is placed higher in the reactivity series than silver (AgAg). Thus, it displaces silver from silver nitrate (AgNO3AgNO_3) to form zinc nitrate (Zn(NO3)2Zn(NO_3)_2) and metallic silver. This is a single displacement reaction.

In part (b), which corresponds to Activity 1.2 in the NCERT textbook, lead nitrate (Pb(NO3)2Pb(NO_3)_2) and potassium iodide (KIKI) exchange their ionic partners (Pb2+Pb^{2+} with II^- and K+K^+ with NO3NO_3^-) to form a yellow precipitate of lead iodide (PbI2PbI_2) and soluble potassium nitrate (KNO3KNO_3). This mutual exchange of ions makes it a double displacement reaction.

Common Mistakes

  1. 1Writing incorrect chemical formulae such as ZnNO3ZnNO_3 instead of Zn(NO3)2Zn(NO_3)_2 or PbIPbI instead of PbI2PbI_2.
  2. 2Forgetting to balance the equations.

Interesting Facts

The yellow precipitate of lead iodide (PbI2PbI_2) formed in the second reaction is often called 'golden rain' when recrystallized from hot water.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2019?

This question carries 3 marks in the CBSE Class 10 Science 2019 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 "Types of Chemical Reactions" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2019 paper?

This is a Short Answer question from Section C in the CBSE Class 10 Science 2019 paper.