The compound formed in the positive test for nitrogen with the Lassaigne solution of an organic compound is(a) Fe₄[Fe(CN)₆]₃ (b) Na₃[Fe(CN)₆(c) Fe(CN)₃ (d) Na₄[Fe(CN)₅NOS]
Answers
Lassaigne’s solution (also known as the sodium fusion test) is performed by mixing a bit of the compound of interest with sodium metal and then heating it up (past melting and then for a bit) and then dumping the result into water and dissolving the solid material. This pretty much removes any organic material and converts things like halogens and nitrogen into anions. Halogens are converted in to the sodium halides (e.g., NaCl, NaBr), sulfur to the sulfide (Na2S), and nitrogen into sodium cyanide (NaCN, with the C coming from the original compound). So, the answer to the question is NaCN. The ‘positive’ test is conducted by taking an aliquot of the resulting solution (after plunging into water) and treating it with FeSO4. The cyanide reacts with the FeSO4 to form sodium ferrous cyanide (Na4[Fe(CN)6].