Displacement Reaction
These notes are based on the chapter Chemical Reactions and Equations from NCERT book based on CBSE syllabus.
When a salt solution of a less reactive metal reacts with a more reactive metal then the more reactive metal displaces the less reactive metal to form a new salt. This reaction is called displacement reaction.
Reactions in which atoms or ions move from one compound to other to form new compound are known as DISPLACEMENT REACTION. Displacement reaction is also known as Substitution Reaction or Single displacement /Replacement Reaction.
A general displacement reaction can be represented using chemical equation as follows:
A + BC → AC + B
In this imaginary reaction, A and B are metals and BC is a compound of metal B. Since A is more reactive than B so it displaces B to make a new compound AC.
Displacement reaction takes place only when A is more reactive than B. If B is more reactive than A, then A will not displace B from BC and reaction will not be taken place.
Activity
Fig Ref: NCERT Text Book
For this activity, you need copper sulphate solution, iron nail and a two test tubes.
- Take 10 mL of copper sulphate solution in two test tubes. Copper sulphate solution is of blue colour.
- Dip an iron nail in one of the test tubes. The second test tube is used as control. This is used to show what happens when no reaction takes place.
- Leave the set up for some time.
- You will notice that the blue colour of the liquid in the test tube disappears and is replaced by light green colour. This happens because of reaction between iron and copper sulphate.
When iron nail is dipped in copper sulphate solution then blue colour of copper sulphate solution changes to light green because of formation of ferrous sulphate. Copper is obtained as brown deposit on the iron nail.
CuSO4(aq) + Fe(s) →FeSO4(aq) + Cu(s)
More Examles of Displacement Reaction
Reaction between copper sulphate and zinc
CuSO4(aq) + Zn(s) → ZnSO4 (aq) + Cu(s)
In this reaction, when zinc granules are kept in copper sulphate solution, the blue colour of solution disappears and solution becomes colourless. This happens because of formation of zinc sulphate which is a colourless substance. In this reaction, zinc displaces copper from copper sulphate because zinc is more reactive than copper.
Reaction between copper sulphate and lead
CuSO4(aq)+ Pb(s)→ PbSO4(aq) + Cu(s)
In this reaction, when lead is put in copper sulphate solution, the blue colour of solution disappears and the solution becomes white because of formation of precipitate of lead sulphate. Lead being more reactive than copper, displaces copper from copper sulphate solution.
Reaction between hydrochloric acid and zinc
When zinc reacts with hydrochloric acid, it gives hydrogen gas and zinc chloride.
In this reaction, zinc displaces hydrogen from hydrochloric acid because zinc is more reactive than hydrogen. This is the reason, zinc displaces hydrogen even from sulphuric acid to form zinc sulphate.
Zn + 2HCl → ZnCl2 + H2
Reaction between copper nitrate and silver
When silver metal is dipped in copper nitrate, no reaction takes place because silver metal is less reactive than copper.
Ag + Cu(NO3 )2 → No reaction takes place
What happens when copper is put in iron sulphate solution? No reaction happens because copper is less reactive than iron. So, copper cannot displace iron from iron sulphate solution.
What happens when copper is put in zinc sulphate solution? No reaction happens because copper is less reactive than zinc. So, copper cannot displace zinc from zinc sulphate solution.