Question

why does blue solution of copper sulphate changes to Green when a piece of iron is added to the solution?

Answer 1

Hey there !

Solution:

This reaction is called Displacement Reaction.

When a metal of higher reactivity is dipped in a low reactive metal's salt solution, the higher reactive metal displaces the less reactive metal from it's salt solution. Hence we can that there is an exchange of ions in the reaction.

General Form of Reaction:

• A + BC => B + AC

Here A is the higher reactive metal, BC is the salt solution.

Now let us write the equation for Copper Sulphate reacting with Iron.

CuSO₄ + Fe => FeSO₄ + Cu

This is of the form : BC + A => AC + B

Hence we can say that this is a displacement reaction.

Reason for colour change is that, Copper sulphate in hydrated form is Blue in colour whereas Iron in hydrated form is green in colour. Hence when there is an exchange in the ions, the iron displaces Copper from it's salt solution. Due to this colour also fades away. Since Iron takes place as the new salt solution, we can see a green coloured solution.

Hence when an iron piece is added to Copper we get a green colour solution of FeSO₄.

Hope my answer helped !