Question

What do you observe on adding zinc granules to freshly prepared ferrous sulphate solution?

Answer 1

- Hint: As we all know zinc is more reactive than ferrous. So, when we add less reactive compound in more reactive compound, then a displacement reaction takes place. As the word displacement means displacing something, here also the same phenomenon occurs.

Complete step by step answer: -
-As we all know, that zinc (Zn) is more reactive than ferrous (Fe) because zinc is a more electropositive element than ferrous. Zinc has a bigger atomic size than iron this it has more no. of electrons and zinc is also a higher transition element (atomic no. 30) than ferrous (atomic no.26) which means reactivity of zinc is more than ferrous.
 - So, when we added zinc to the solution of ferrous sulphate, the colour of ferrous sulphate solution changes because zinc is more reactive than ferrous, therefore when we add zinc granules in ferrous sulphate solution, it displaces ferrous sulphate solution and forms zinc sulphate solution.
 - When zinc sulphate displaces ferrous sulphate from its solution a grey coloured precipitate of ferrous and then a colourless solution of zinc sulphate is formed.
- So, in this whole process lead formation of zinc sulphate and ferrous is produced.
$Zn+FeS{{O}_{4}}\xrightarrow{{}}Fe+ZnS{{O}_{4}}$
- Another thing is why we use freshly prepared ferrous sulphate solution because on exposure to the atmosphere, it is oxidized to ferric sulphate which will not give brown ring.
 [brown ring:- A brown ring will from at the junction of the two layers indicating the presence of nitrate ion and freshly prepares ferrous sulphate is used in brown ring because is ferrous sulphate is stored or it is the old one then it reacts with atmospheric and get oxidized to from corrosive brown yellow coating of basic ferric sulphate, which is an adduct of ferric oxide and ferric sulphate.]

Note: -
-Displacement reaction is basically a chemical reaction in which a more reactive element displaces a less reactive element from its compound and forms a completely new compound. (Both metal or nonmetal).
-You must know the relative reactivity of one element with respect to the other.
-After swapping the displacing elements try righting the correct chemical formulae by keeping the ionic configuration in mind.