Answer to Question #182956 in Organic Chemistry for smart ben

Question

Nitrogen in organic compound is tested by the addition of few drops of saturated iron (III) sulphate solution to small portion of sodium fusion filtrate. Diluted hydrogen tetraoxosuphate (VI) is then added to the later solution leading to the formation of Prussian blues colour or ppt. signalling the presence of nitrogen. Show these steps using equations and names your final product.

Answer 1

If nitrogen is present in the compound, the sodium extract would contain sodium cyanide formed during fusion. On adding the required reagents, sodium cyanide reacts to form ferric-ferrocyanide which has prussian blue colour.

• Na + C + N → NaCN
• 2Na + S → Na₂S
• Na + X → NaX ( X= Cl, Br, or I)

1. Fe²⁺ + 6CN^– → [Fe(CN)₆]^4-
2. Fe²⁺ + H⁺→ Fe³⁺ + e^–
3. [Fe(CN)₆]^4- + 4Fe³⁺ → Fe₄[Fe(CN)₆].H₂O

Test for Sulphur

The extract is treated with sodium nitroprusside. The appearance of violet colour indicates the presence of sulphur.

The following reaction occurs:

S^2- + [Fe(CN)₅NO]^2- → [Fe(CN)₅NOS]^4-