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Part of OC-10 — Practical Organic Chemistry

Fill in the Blanks — Active Recall Practice

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  1. In Lassaigne's test, when both nitrogen and sulfur are present, the compound ______ (NaSCN / NaCN) is formed, and FeCl3 gives ______ (blood-red / Prussian blue) color.

  2. AgCl is ______ (white/yellow) in color and is ______ (soluble/insoluble) in dilute NH3.

  3. AgI is ______ (white/yellow) in color and is ______ (soluble/insoluble) in NH3 at any concentration.

  4. The KMnO4/oxalic acid titration is ______ (self-indicating / requires methyl orange) and is performed at ______ (25 °C / 60–70 °C).

  5. The iodoform test is positive for ______ (all ketones / methyl ketones only), giving ______ (yellow / white) crystals of CHI3.

  6. Tollens' reagent gives a ______ (silver mirror / red precipitate) with aldehydes, but ______ (positive / negative) result with ketones.

  7. 2,4-DNP test gives an orange precipitate with ______ (aldehydes only / both aldehydes and ketones).

  8. Before testing for halogens in Lassaigne's extract when nitrogen is present, the extract must first be boiled with ______ (HNO3 / HCl) to destroy ______.

  9. Carbylamine test: CHCl3 + KOH gives foul-smelling ______ (isocyanide / amide) with ______ (primary / secondary) amines.

  10. The brown ring test detects ______ (NO3- / SO42-). The ring forms due to formation of ______ complex.

Answers:

  1. NaSCN; blood-red
  2. White; soluble
  3. Yellow; insoluble
  4. Self-indicating; 60–70 °C
  5. Methyl ketones only; yellow
  6. Silver mirror; negative
  7. Both aldehydes and ketones
  8. HNO3; NaCN (and Na2S)
  9. Isocyanide; primary
  10. NO3-; [Fe(H2O)5(NO)]2+ (brown ring complex)

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