|
A substitution or displacement reaction is a chemical change in which atoms of one element replace the atoms of another element from the molecules of a compound. Elements which are higher in the Activity Series displace those elements which are placed below them. More electro positive elements displace lesser electro positive elements. Conversely, higher electro negative elements will displace lesser electro negative elements. For e.g.,
- When an iron knife is dipped in an aqueous solution of copper sulphate, a layer of reddish brown precipitate is formed on the iron knife. The iron from the knife being more reactive than copper, displaces it from the copper sulphate solution. The copper so separated gets collected on the surface of iron knife.
- When small clean pieces of magnesium are added into dilute sulphuric acid, magnesium sulphate and hydrogen are formed. Atoms of magnesium displace the atoms of hydrogen from sulphuric acid.
- When a colourless solution of potassium iodide is passed through a colourless solution of chloroform, the chloroform layer becomes purple. Chlorine being more electro-negative than iodine, displaces iodine from potassium iodide.
The iodine so liberated, dissolves in the chloroform, giving it a purple colour.
| 
