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Types of Chemical Change or Chemical Reaction - Double Displacement Reaction

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Topics

  • Introduction
  • Experiment

Introduction:

A double displacement reaction, also known as a double replacement reaction, occurs when the cations and anions of two aqueous ionic compounds exchange places, resulting in the formation of two new compounds.

AB + CD → AD + CB

Here, A and C represent positively charged cations, while B and D are negatively charged anions. These reactions typically occur in aqueous solutions, and at least one of the products is usually a solid precipitate, a gas, or a molecular compound such as water, making the reaction proceed.

For example, when potassium nitrate (KNO₃) reacts with aluminium chloride (AlCl₃), they exchange ions to produce aluminium nitrate [Al(NO₃)₃] and potassium chloride (KCl):

KNO₃ + AlCl₃ ⇌ Al(NO₃)₃ + KCl

Experiment

1. Aim: To observe a double displacement reaction where two aqueous ionic compounds exchange ions, leading to the formation of an insoluble precipitate.

2. Requirements

  • Apparatus: test tubes, beaker, dropper, stirring rod.
  • Chemicals: Potassium iodide (KI) solution, lead(II) nitrate [Pb(NO₃)₂] solution.

3. Procedure

  • Take potassium iodide (KI) solution in a test tube.
  • Add lead(II) nitrate [Pb(NO₃)₂] solution slowly while stirring.
  • Observe the formation of a yellow precipitate of lead(II) iodide (PbI₂), indicating a chemical reaction.

2KI(aq) + Pb(NO₃)₂(aq) → 2KNO₃(aq) + PbI₂(s)

4. Conclusion: A double displacement reaction occurs when the cations and anions of two ionic compounds exchange places, forming two new compounds. In this reaction, the insoluble lead(II) iodide (PbI₂) precipitate confirms the formation of a new substance, demonstrating the concept of precipitation reactions in aqueous solutions.

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