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 is used to detect the presence of extra elements (like nitrogen, sulfur, halogens) in organic compounds. In this test, organic compounds are fused with sodium to convert these elements into their ionic detectable forms:

- Nitrogen → NaCN
- Sulfur → Na₂S
- Halogens → NaX (NaCl, NaBr, NaI)

Now evaluate the reactions:
- Option (1): Formation of Na₂S → Used to test sulfur — part of Lassaigne's test.
- Option (2): Formation of NaX (halide salts) → Used to test halogens — part of Lassaigne's test.
- Option (3): This is a reduction reaction of CuO by carbon — NOT related to detection of any element in organic analysis. Not part of Lassaigne's test.
- Option (4): Formation of NaCN — used for nitrogen detection — is part of Lassaigne's test.

Therefore, only option (3) is unrelated to Lassaigne's test.