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Tests for Acids, Esters and Amides

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Estimated time: 5 minutes
CBSE: Class 12

Key Points: Tests for Acids, Esters, and Amides

Tests for Acids (Carboxylic acids):

 
Test Observation Inference
NaHCO₃ test Brisk CO₂ effervescence Presence of –COOH (acid)
Fluorescein reaction Heated with conc. H₂SO₄ + Resorcinol → red solution with intense green fluorescence Dicarboxylic acid
Anhydride formation White shiny needles on sides of inverted funnel Dicarboxylic acid

Distinction: Alcohol vs Phenol vs Carboxylic Acid:

  • Alcohol: reacts with Na → H₂ gas; does NOT react with NaOH or NaHCO₃
  • Phenol: reacts with Na + NaOH → H₂; does NOT react with NaHCO₃
  • Carboxylic acid: reacts with Na, NaOH, and NaHCO₃ (gives CO₂)

Tests for Esters:

  • \[ \mathrm{RCOOR}' + \mathrm{NaOH} + \text{Phenolphthalein (Pink)} \xrightarrow{\Delta} \mathrm{RCOOH} + \mathrm{R}'\mathrm{OH} \text{ (Colorless solution)} \]
  • Esters have sweet/fruity smell

Test for Acid amide:

Acid amides (1°) give smell of ammonia when with alkali.

\[ \mathrm{R} - \overset{\displaystyle \mathrm{O}}{\overset{||}{\mathrm{C}}} - \mathrm{NH}_2 \xrightarrow[\Delta]{\mathrm{NaOH}} \mathrm{R} - \overset{\displaystyle \mathrm{O}}{\overset{||}{\mathrm{C}}} - \mathrm{ONa} + \mathrm{NH}_3 \]

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