Carboxylic Acids – The Sour Compounds

📚 Key Concepts

🔹 Real-Life Example

The sour taste of vinegar comes from acetic acid, the tangy flavor in citrus fruits comes from citric acid, and the pain from ant bites comes from formic acid. All these have the -COOH functional group that makes them acidic in nature.

Carboxylic Acids: Organic compounds containing the carboxyl functional group (-COOH). They are weak acids that partially ionize in aqueous solution to release H⁺ ions.

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🧪 Properties and Behavior

🔸 Physical Properties

  • Acidic nature: Release H⁺ ions in water
  • Higher boiling points: Due to hydrogen bonding
  • Solubility: Lower members soluble in water
  • Smell: Often have distinctive odors

🔸 Chemical Properties

Acidic Behavior: CH₃COOH ⇌ CH₃COO⁻ + H⁺

Reaction with Metals: 2CH₃COOH + Zn → (CH₃COO)₂Zn + H₂↑

Reaction with Bases: CH₃COOH + NaOH → CH₃COONa + H₂O

Reaction with Carbonates: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂↑ + H₂O

🧪 Important Carboxylic Acids

🔸 Formic Acid (HCOOH)

Sources:

  • Ant bites and bee stings
  • Stinging nettle plants

Properties:

  • Simplest carboxylic acid
  • Causes burning sensation
  • Strong reducing agent
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🔸 Acetic Acid (CH₃COOH)

Preparation: Oxidation of ethanol: C₂H₅OH + O₂ → CH₃COOH + H₂O (In presence of bacteria – fermentation)

Properties:

  • 5-8% solution is vinegar
  • Pure form called glacial acetic acid
  • Weak acid (partially ionizes)

Uses:

  • Food preservative (vinegar)
  • Manufacturing acetates
  • Laboratory reagent

🔍 Advanced: Esterification

Carboxylic acids react with alcohols to form esters: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O This reaction is reversible and requires acid catalyst.