Na + S → Na2S (in fusion)

Test 1 — Sodium nitroprusside: Na2S + Na2[Fe(CN)5NO] → Na4[Fe(CN)5NOS] → purple/violet color The S2- ion replaces one coordination position, changing the color of the complex. This is extremely sensitive — even traces of S2- give a noticeable purple.

Test 2 — Lead acetate: Na2S + Pb(CH3COO)2 → PbS (black precipitate) + 2CH3COONa PbS is one of the most insoluble salts — extremely reliable test.

Test 3 — Acidify and check for H2S: Na2S + HCl → 2NaCl + H2S (rotten egg smell, turns lead acetate paper black)

When both N and S are present: The primary product of fusion is NaCNS (sodium thiocyanate) rather than separate NaCN and Na2S. Test with FeCl3 gives blood-red Fe(SCN)3 instead of Prussian blue. Solution: use excess sodium in the fusion to ensure: Na + C + N → NaCN and Na + S → Na2S (both formed separately).