Double Displacement Reaction - Teachoo.jpg

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-

Formation of Barium Sulphate-Teachoo-01.jpg

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

DOUBLE DISPLACEMENT REACTION TAKES PLACE BETWEEN LEAD NITRATE AND POTASSIUM IODIDE TO FORM POTASSIUM NITRATE AND YELLOW PRECIPITATE OF LEAD IODIDE - Teachoo.jpg

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)

           

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo