Three students, Manish, Ramesh and Rajini were determining the extra elements present in an organic compound given by their teacher. They prepared the Lassaigne's extract (L.E.) independently by the fusion of the compound with sodium metal. Then they added solide `FeSO_(4)` and dilute sulphuric acid to a part of Lassaigne's extract. Manish and Rajni obtained prussian blue colour but Ramesh got red colour.
Ramesh repeated the test with the same Lassaigne's extract, but again got red colour only. They were surprised and went to their teacher and told him about their observation. Teacher asked them to think over the reason for this. Can you help them by giving the reason for this observation. Also, write the chemical equations to explain the formation of compounds of different colour.

Explanation

In the preparation of the Lassaigne's Extract for the organic compound containing N and S, sodium thiocyanate (NaSCN) is formed if sodium metal is not taken in excess.
`ubrace(C+N+S)_("organic compound")+Na overset("Fusion")(rarr) underset("Sod. thiocyanate")(NaSCN)`
In case, sodium metal is taken in excess, then `NaSCN` reacts with the metal to form a mixture of `NaCN` and `Na_(2)S`.
`NaSCN+2Na overset("Fusion")(rarr) underset("Sod. cyanide")(NaCN)+underset("Sod. sulphide")(Na_(2)S)`
In the first case, `NaSCN` reacts with `Fe^(3+)` ions formed by the oxidation of `Fe^(2+)` ions `(FeSO_(4))` to form `Fe(SCN)_(3)` which has a blood red colour.
`Fe^(3+)+3NaSCN rarr underset("(Blood red colour)")((Fe(SCN)_(3)))+3Na^(+)`
In the second case, `NaCN` takes part in the chemical reactions to form `Fe_(4) [Fe(CN)_(6)]_(3)` which has a prussian blue colour.
`2NaCN+FeSO_(4) rarr Fe(CN)_(2)+Na_(2)SO_(4)`
`Fe(CN)_(2)+4NaCN rarr underset("Sod. ferrocyanide")(Na_(4)[Fe(CN)_(6)])`
`3Na_(4)[Fe(CN)_(6)]+4Fe^(3+) rarr Fe_(4)underset(("Ferric ferrocyanide"),("Prussian blue"))([Fe(CN)_(6)]_(3)+12 Na^(+))`
In the light of the above infomration, it seems that both Manish and Rajni used excess of sodium in the preparation of the extract and the product formed was ferric ferrocyanide carrying a prussian blue or deep blue colouration. however, Ramesh used the metal in lesser amount for the preparation of the extract and ended with `Fe(SCN)_(3)` which has blood red colouration.