Question

Which one of the following reactions does NOT belong to “Lassaigne's test”?

• A. $2Na + S$ \(\xrightarrow{\Delta}\) $Na_2S$
• B. $Na + X$ \(\xrightarrow{\Delta}\) $NaX$
• C. $2CuO + C$ \(\xrightarrow{\Delta}\) $2Cu + CO_2$
• D. $Na + C + N$ \(\xrightarrow{\Delta}\) $NaCN$

Hint:

Lassaigne’s test involves converting N, S, and halogens into ionic compounds using sodium for easy detection. Redox reactions like CuO + C are not included.

Answer 1

The Correct Option is C

Lassaigne's test identifies extra elements (nitrogen, sulfur, halogens) in organic compounds. Organic compounds are heated with sodium, converting these elements into ionic forms for detection.

- Nitrogen is converted to NaCN.
- Sulfur is converted to Na₂S.
- Halogens are converted to NaX (e.g., NaCl, NaBr, NaI).

Evaluation of reactions:

- Option (1): Formation of Na₂S is used for sulfur detection, a component of Lassaigne's test.
- Option (2): Formation of NaX (halide salts) is used for halogen detection, a component of Lassaigne's test.
- Option (3): This reaction involves the reduction of CuO by carbon and is unrelated to organic elemental analysis or Lassaigne's test.
- Option (4): Formation of NaCN is used for nitrogen detection, a component of Lassaigne's test.

Consequently, only option (3) is not part of Lassaigne's test.