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medium importancemedium difficulty4 min

Precipitation Reaction

A precipitation reaction is a reaction in which an insoluble solid called a precipitate forms from solutions.

In one line: Precipitate means solid falls out.

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Understand it

Precipitation is not a completely separate pattern from double displacement; it is the visible result when one of the new products does not dissolve in water. The solid settles or makes the mixture cloudy.

Example

Mixing lead nitrate and potassium iodide gives yellow lead iodide.

Rule to remember

A precipitate is an insoluble solid formed when aqueous ions combine to make an insoluble product.

See it worked out

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

Worked example

  1. 1Pb(NO3)2 + 2KI → PbI2(s) + 2KNO3.
  2. 2PbI2 is insoluble, so it appears as a precipitate.

Method you can reuse

  1. 1Mix the solutions mentally.
  2. 2Check whether any product is insoluble in water.
  3. 3If a solid forms, call it a precipitate.

Sketch it in your answer

Show two clear solutions becoming cloudy and a solid settling at the bottom.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Two clear salt solutions are mixed and a solid settles at the bottom. What is the solid called?

Think first, then show answer
The solid is called a precipitate, and the reaction is a precipitation reaction.

Common wrong answer

Saying it is decomposition because a solid appears.

Why it loses marks: The reactants are two solutions, not one compound breaking apart.

Don't mix this up

Students may write only the salt exchange and miss the insoluble solid formed in the reaction.

Exam tip

If a question mentions a solid settling down or a cloudy mixture, think precipitate.

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

Questions may ask you to identify the precipitate or to state why the mixture becomes cloudy.
  1. 1

    Enough for 1 mark

    A precipitation reaction is a reaction in which an insoluble solid called a precipitate forms from solutions.

  2. 2

    Add for 2 marks

    Example: Mixing lead nitrate and potassium iodide gives yellow lead iodide.

  3. 3

    Add for 3 marks

    Precipitation is not a completely separate pattern from double displacement; it is the visible result when one of the new products does not dissolve in water.

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