ERROR: Concluding Prussian blue in Lassaigne's test when compound contains both N and S. CORRECT: N + S together → NaSCN → FeCl3 gives blood-red, NOT Prussian blue. Prussian blue requires NaCN (only when N is present WITHOUT S).

ERROR: Saying the iodoform test is positive for ALL ketones. CORRECT: Iodoform test is positive ONLY for methyl ketones (CH3CO-R), acetaldehyde, ethanol, and secondary alcohols of the type CH3CHOH-R. 3-Pentanone (no CH3 on C=O) is NEGATIVE.

ERROR: Not boiling Lassaigne's extract with HNO3 before the AgNO3 halogen test when N or S is present. CORRECT: NaCN → AgCN (white ppt, mimics AgCl); Na2S → Ag2S (black ppt). These must be destroyed with HNO3 first.

ERROR: Using an indicator in KMnO4/oxalic acid titration. CORRECT: The titration is self-indicating. KMnO4 itself acts as the indicator. No phenolphthalein, methyl orange, or starch is needed.

ERROR: Performing KMnO4/oxalic acid titration at room temperature. CORRECT: The reaction is too slow at room temperature. The mixture must be heated to 60–70 °C. Using ice bath or room temperature gives inaccurate (often false early endpoint) results.

ERROR: Confusing AgBr (pale yellow) with AgI (yellow) colors. CORRECT: AgBr is pale/cream yellow and partially soluble in concentrated NH3. AgI is distinctly yellow and insoluble in NH3 at any concentration.

ERROR: Thinking HCl can be used instead of HNO3 for acidification before the AgNO3 test. CORRECT: HCl would introduce Cl- ions, giving false positive AgCl precipitate. Only dilute HNO3 must be used because Ag+ does not form insoluble salts with NO3-.

ERROR: Assuming carbylamine test works for secondary and tertiary amines. CORRECT: Carbylamine test (CHCl3 + KOH → foul isocyanide smell) is specific for PRIMARY amines (-NH2) only. Secondary and tertiary amines cannot form isocyanides via this mechanism.