Displacement And Double Displacement Reaction

DISPLACEMENT REACTION

• Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions.
• A more reactive element displaces a less reactive element from its compound.                                                                                       

• EXAMPLE –Iron has displaced or removed another element, copper, from copper sulphate solution.

• Zinc and lead are more reactive elements than copper.

• lead and zinc displace copper from its compounds.                                                                                                                                                                                                                                                                                                                         

ACTIVITY 1.9 

Experiment to show Displacement of copper using iron

• Apparatus– 
  • 3 iron nails, 2 test tubes, copper sulphate solution
• Procedure
  • Take about 10 ml copper sulphate solution in two test tubes.
  • Tie two iron nails with a thread and immerse them carefully in the copper sulphate solution in test tube B for about 20 minutes.
  • Keep one iron nail aside for comparison. 
  • After 20 minutes, take out the iron nails from the copper sulphate solution.
    

• Compare the intensity of the blue color of copper sulphate solutions in test tube (A) and (B).
• Also, compare the color of the iron nails dipped in the copper sulphate solution with the one kept aside.

Observation–The iron nail becomes brownish in color and the blue color of copper sulfate solution fade.

• Reason- iron has displaced or removed another element of copper, from copper sulphate solution.                                      

DOUBLE DISPLACEMENT REACTION

• The reactions in which there is an exchange of ions between the reactants are called double displacement reactions.
• A double displacement reaction usually occurs in solution and one of the products, being insoluble, precipitates out (separates as a solid).

• EXAMPLE: 1 AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)             

 The white precipitate of AgCl is formed by the reaction of Cl- and Ag+

• Example: 2

• NOTE – Any reaction that produces a precipitate can be called a precipitation reaction.
• AgNO3(aqueous) + KCl(aqueous) —–AgCl(precipitate) + KNO3(aqueous)
• AgNO3(aqueous) + NaCl(aqueous) —- AgCl↓ + NaNO3 (aqueous)     

        ACTIVITY  1.10 

Experiment- Double displacement reaction

• Take about 3 ml of sodium sulfate solution in a test tube.
• In another test tube, take about 3 ml of barium chloride solution.
•  Mix the two solutions
• What do you observe?
• a white substance, which is insoluble in water, is formed. 
• The white precipitate of BaSO4 is formed by the reaction of  SO4²- and Ba2+.
• Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)       

IMPORTANT QUESTIONS AND ANSWERS:

• displacement and double displacement                                                                                                   1.  Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions.        
  Answer.
  
• A displacement reaction is a reaction in which more reactive metal can displace less reactive metal from its salt solution.
• Double displacement reaction are those reactions in which compounds exchange their ions to form two new compounds
•  (i) Double displacement reaction, (ii) Displacement reaction. 

2.Express the following facts in the form of a balanced chemical equation :
“When a strip of copper metal is placed in a solution of silver nitrate, metallic silver is precipitated and a solution containing copper nitrate is formed”. 

ANS:The silver nitrate reacts with copper to form hair like crystals of silver metal and a blue solution of copper nitrate:

2 AgNO₃ + Cu → Cu(NO₃)₂ + 2 Ag.