It is a type of chemical reaction in which two compounds react and their positive and negative ions switch places to form 2 new products.

In easy language

In double displacement reaction, there is displacement of 2 substances to form 2 new products

 

Example 1

When Sodium Sulphate solution is mixed with Barium Chloride solution It forms Barium Sulphate and Sodium Chloride solution.

Explanation: The positive and negative ions of Sodium Sulphate (Na 2 SO 4 ) are Na + and (SO 4 ) 2-

The positive and negative ions of Barium Chloride (BaCl 2 ) are Ba 2+ and Cl - .

The positive ions of both the compounds switch places,

Na + combines with Cl - , forming  NaCl

Ba 2+ combines with (SO 4 ) 2- forming BaSO 4

 

In this reaction, white Barium Sulphate is formed as a precipitate

(Insoluble solid is called precipitate)

 

This Barium Sulphate (BaSO 4 ) is formed because of the reaction of positively charged ions of Barium (Ba 2+ ) and negatively charged ions of Sulphate (SO 4 ) 2- .



Note - A reaction in which a precipitate is formed is a precipitate reaction .

 

The above reaction is also an example of precipitate reaction since a precipitate of  BaSO 4 is formed. 

 

Example 2

When Potassium Iodide solution is added to Lead Nitrate solution

A yellow precipitate of Lead Iodide is formed along with Potassium Nitrate solution

 

Explanation

The positive and negative ions of Potassium iodide (KI) are K + and I -

The positive and negative ions of Lead Nitrate (Pb(NO 3 ) 2 ) are Pb 2+ and NO 3 -

 

The positive ions of both the compounds switch places,

K + combines with NO 3 - , forming  KNO 3

Pb 2+ combines with I - forming PbI 2

KI + Pb(NO 3 ) 2 →  KNO 3 + PbI 2

                                                                                                 (Yellow precipitate)

           

  1. Class 10
  2. Chapter 1 Class 10 - Chemical Reactions and Equations (Term 1)

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo