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Double Displacement Reaction

A double displacement reaction is a reaction in which two compounds exchange ions to form two new compounds.

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Student-friendly explanation

This reaction usually happens in aqueous solution. The ions swap partners, and sometimes one product is an insoluble solid. That is why many precipitation reactions are double displacement reactions.

How to write this in exams

  1. 1

    Start with the exact idea

    A double displacement reaction is a reaction in which two compounds exchange ions to form two new compounds.

  2. 2

    Then show how to use it

    1. Check whether both reactants are compounds. 2. See whether ions exchange partners. 3. If yes, name it double displacement.

  3. 3

    Add one concrete example

    Sodium sulphate solution and barium chloride solution form barium sulphate and sodium chloride.

  4. 4

    Avoid this incomplete answer

    Calling it displacement because a new solid appears. That is wrong because displacement changes one element, while double displacement swaps ions.

Definition

A double displacement reaction is a reaction in which two compounds exchange ions to form two new compounds.

Example

Sodium sulphate solution and barium chloride solution form barium sulphate and sodium chloride.

Rule to remember

General pattern: AB + CD → AD + CB.

Memory hook

Two compounds swap partners.

Examples and method

Worked example

Na2SO4 + BaCl2 → BaSO4 + 2NaCl. The ions exchange partners, so the reaction is double displacement.

Method to apply

1. Check whether both reactants are compounds. 2. See whether ions exchange partners. 3. If yes, name it double displacement.

Diagram support

Draw two aqueous reactants on the left and two new products on the right, marking any solid formed.

How CBSE asks it

You may be asked to identify the reaction from a salt-solution mix or from a written equation.

Avoid common mistakes

Common confusion

Students may think only one substance changes. In fact, both compounds exchange ions.

Common wrong answer

Calling it displacement because a new solid appears. That is wrong because displacement changes one element, while double displacement swaps ions.

Exam tip

If two solutions are mixed and ions swap partners, check whether a precipitate forms.

Quick check

When sodium sulphate and barium chloride solutions are mixed and a white solid forms, what reaction is this?

It is a double displacement reaction because the two compounds exchange ions and a new insoluble product forms.

Answer writing and exam use

1-mark answer

A double displacement reaction is a reaction in which two compounds exchange ions to form two new compounds.

2-mark answer

A double displacement reaction is a reaction in which two compounds exchange ions to form two new compounds. General pattern: AB + CD → AD + CB. Sodium sulphate solution and barium chloride solution form barium sulphate and sodium chloride.

3-mark answer

This reaction usually happens in aqueous solution. The ions swap partners, and sometimes one product is an insoluble solid. That is why many precipitation reactions are double displacement reactions. General pattern: AB + CD → AD + CB. Na2SO4 + BaCl2 → BaSO4 + 2NaCl. The ions exchange partners, so the reaction is double displacement. You may be asked to identify the reaction from a salt-solution mix or from a written equation. Calling it displacement because a new solid appears. That is wrong because displacement changes one element, while double displacement swaps ions.
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