In Lassaigne's test, organic elements are converted to ionic forms by fusion with sodium metal: N → NaCN, S → Na2S, halogen → NaX.

When both nitrogen AND sulfur are present together, NaSCN (sodium thiocyanate) is formed instead of separate NaCN and Na2S.

FeCl3 gives Prussian blue only when nitrogen alone is present (as NaCN); with both N and S (as NaSCN), it gives blood-red Fe(SCN)3.

Before the AgNO3 halogen test, the Lassaigne extract must be boiled with dilute HNO3 to destroy NaCN and Na2S which would otherwise cause interference.

AgCl is white and soluble in dilute NH3; AgBr is pale yellow and partially soluble in concentrated NH3; AgI is yellow and insoluble in NH3 at any concentration.

The 2,4-DNP test detects any carbonyl (C=O) group but cannot distinguish aldehydes from ketones; Tollens' test is needed for that distinction.

The iodoform test (I2/NaOH → yellow CHI3) is specific for methyl ketones (CH3CO-R) and does not work with non-methyl ketones like 3-pentanone.

The KMnO4/oxalic acid titration is self-indicating (no external indicator needed), requires 60–70 °C, and the balanced equation is 5C2O42- + 2MnO4- + 16H+ → 10CO2 + 2Mn2+ + 8H2O.

Acetanilide is prepared by acetylation of aniline with acetic anhydride and is used as a protected amino compound for selective para-nitration in synthesis.

The carbylamine test (CHCl3 + KOH → foul isocyanide) is specific for primary amines (-NH2) only; secondary and tertiary amines give negative results.