explain lassaigne's test for the detection of sulphur and halogens(3 marks)
Answers
Test for Sulphur:
If sulphur is present in the organic compound, sodium fusion will convert it into sodium sulphide. Sulphide ions are readily identified using sodium nitroprusside.
Na + S → Na2S
Na2S + Na2[Fe(CN)5NO] → Na4[Fe(CN)5NOS]
Test for Halogen:
Halogens present in an organic compound forms sodium halide on fusion with sodium metal. Sodium halide extracted with water can be easily identified by adding silver nitrate solution after acidifying with dil. HNO3.
If chlorine is present, a white curdy precipitate soluble in ammonium hydroxide solution is formed.
Na + Cl → NaCl
NaCl + AgNO3 → AgCl + NaNO3
If bromine is present, an yellowish white precipitate sparingly soluble in ammonium hydroxide solution is formed.
Na + Br → NaBr
NaBr + AgNO3 → AgBr + NaNO3
If iodine is present, an yellow precipitate insoluble in ammonium hydroxide solution is formed.
Na + I → NaI
NaI + AgNO3 → AgI + NaNO3