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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.

In one line: Two compounds swap partners.

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Understand it

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.

Example

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

Rule to remember

General pattern: AB + CD → AD + CB.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1Na2SO4 + BaCl2 → BaSO4 + 2NaCl.
  2. 2The ions exchange partners, so the reaction is double displacement.

Method you can reuse

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

Sketch it in your answer

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

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

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

Think first, then show answer
It is a double displacement reaction because the two compounds exchange ions and a new insoluble product forms.

Common wrong answer

Calling it displacement because a new solid appears.

Why it loses marks: Displacement changes one element, while double displacement swaps ions.

Don't mix this up

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

Exam tip

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

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

You may be asked to identify the reaction from a salt-solution mix or from a written equation.
  1. 1

    Enough for 1 mark

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

  2. 2

    Add for 2 marks

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

  3. 3

    Add for 3 marks

    This reaction usually happens in aqueous solution.

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