Lassaigne's Test for Nitrogen & Sulphur Together

Formula / Core Reaction:

$$\text{Na} + \text{C} + \text{N} + \text{S} \xrightarrow{\Delta} \text{NaSCN}$$

$$\text{Fe}^{3+} + 3\text{NaSCN} \rightarrow [\text{Fe}(\text{SCN})]_3 \quad \text{or} \quad [\text{Fe}(\text{SCN})]^{2+} + 3\text{Na}^+$$

Concept: When nitrogen and sulfur are simultaneously present in an organic compound without an excess of sodium metal, sodium thiocyanate ($$\text{NaSCN}$$) forms, yielding a blood-red complex upon adding $$\text{Fe}^{3+}$$ ions.

Notation / Key Observation:

• $$\text{NaSCN}$$: Sodium thiocyanate;
• $$[\text{Fe}(\text{SCN})]^{2+}$$: Iron(III) thiocyanate complex (Blood-red coloration);
• Note: If excess $$\text{Na}$$ is used, $$\text{NaSCN}$$ decomposes into $$\text{NaCN}$$ and $$\text{Na}_2\text{S}$$, giving individual tests for nitrogen and sulfur separately.