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Precipitation Reaction

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

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Student-friendly explanation

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.

How to write this in exams

  1. 1

    Start with the exact idea

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

  2. 2

    Then show how to use it

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

  3. 3

    Add one concrete example

    Mixing lead nitrate and potassium iodide gives yellow lead iodide.

  4. 4

    Avoid this incomplete answer

    Saying it is decomposition because a solid appears. That is wrong because the reactants are two solutions, not one compound breaking apart.

Definition

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

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.

Memory hook

Precipitate means solid falls out.

Examples and method

Worked example

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

Method to apply

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

Diagram support

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

How CBSE asks it

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

Avoid common mistakes

Common confusion

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

Common wrong answer

Saying it is decomposition because a solid appears. That is wrong because the reactants are two solutions, not one compound breaking apart.

Exam tip

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

Quick check

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

The solid is called a precipitate, and the reaction is a precipitation reaction.

Answer writing and exam use

1-mark answer

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

2-mark answer

A precipitation reaction is a reaction in which an insoluble solid called a precipitate forms from solutions. A precipitate is an insoluble solid formed when aqueous ions combine to make an insoluble product. Mixing lead nitrate and potassium iodide gives yellow lead iodide.

3-mark answer

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. A precipitate is an insoluble solid formed when aqueous ions combine to make an insoluble product. Pb(NO3)2 + 2KI → PbI2(s) + 2KNO3. PbI2 is insoluble, so it appears as a precipitate. Questions may ask you to identify the precipitate or to state why the mixture becomes cloudy. Saying it is decomposition because a solid appears. That is wrong because the reactants are two solutions, not one compound breaking apart.
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