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)