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ICSE Class 9 Chemistry Question 5 of 18

Chemical Changes & Reactions — Question 13

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Question 13

Define a displacement reaction with a suitable example. State how it is represented. Give a reason why zinc displaces hydrogen from dilute sulphuric acid but copper does not.

Answer

A chemical reaction which takes place when an element [or radical] has replaced another element in a compound is known as Displacement reaction

It is represented as :

X + YZ ⟶ Y + XZ

e.g.,

Magnesium + Copper [II] sulphate ⟶ Magnesium sulphate + Copper

Mg + CuSO4 ⟶ MgSO4 + Cu

As a more electropositive metal displaces a less electropositive metal from it's aq. soln. therefore, zinc being more electropositive is placed above [H] in activity series and displaces hydrogen from dilute sulphuric acid whereas copper being less electropositive is placed below [H] in electrochemical series and cannot displace hydrogen from sulphuric acid.