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ChemistryNEET 2025Qualitative and quantitative analysis

Purification and Characterisation of Organic Compounds

Which one of the following reactions does not belong to Lassaigne's test?

  1. A.Na+C+N→ΔNaCN\mathrm{Na + C + N \xrightarrow{\Delta} NaCN}
  2. B.2Na+S→ΔNa2S\mathrm{2Na + S \xrightarrow{\Delta} Na_2S}
  3. C.Na+X→ΔNaX\mathrm{Na + X \xrightarrow{\Delta} NaX}
  4. D.2CuO+C→Δ2Cu+CO2\mathrm{2CuO + C \xrightarrow{\Delta} 2Cu + CO_2}✓

Solution

Fusing sodium with the compound gives NaCN, Na2S\mathrm{Na_2S} and NaX from nitrogen, sulphur and halogen respectively — the basis of Lassaigne's test. Oxidising carbon with CuO to CO2\mathrm{CO_2} is the Liebig combustion method for estimating carbon, not Lassaigne's.

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