Carboxylic Acids

🔹 1. Definition of Carboxylic Acids

• Carboxylic acids are a group of organic compounds that contain the carboxyl functional group: –COOH.
• General formula: C_nH_2n+1COOH
• The carboxyl group is made up of a carbonyl group (C=O) and a hydroxyl group (–OH) attached to the same carbon atom.

Example:

• Methanoic acid: HCOOH
• Ethanoic acid: CH₃COOH

🔹 2. General Properties of Carboxylic Acids

Physical Properties:

• Have sharp, sour smells (like vinegar).
• Soluble in water (small-chain acids), forming acidic solutions.
• Have higher boiling points due to hydrogen bonding between molecules.

Chemical Properties:

• They behave as weak acids.
• They release hydrogen ions (H⁺) in water.
• Show typical acidic reactions, forming salts.

🔹 3. Reactions of Carboxylic Acids

Carboxylic acids react with metals, metal oxides, carbonates, hydrogen carbonates, and alcohols.

🔸 a) With Metals

Reaction Type: Acid + Metal → Salt + Hydrogen gas

Example:
Ethanoic acid + Magnesium → Magnesium ethanoate + Hydrogen
2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂

🔹 Observation: Effervescence (bubbles of hydrogen gas)

🔸 b) With Metal Oxides

Reaction Type: Acid + Metal Oxide → Salt + Water

Example:
Ethanoic acid + Copper(II) oxide → Copper(II) ethanoate + Water
2CH₃COOH + CuO → (CH₃COO)₂Cu + H₂O

🔸 c) With Metal Carbonates

Reaction Type: Acid + Carbonate → Salt + Water + Carbon dioxide

Example:
Ethanoic acid + Calcium carbonate → Calcium ethanoate + Water + CO₂
2CH₃COOH + CaCO₃ → (CH₃COO)₂Ca + H₂O + CO₂

🔹 Observation: Effervescence due to CO₂ gas, turns limewater milky

🔸 d) With Metal Hydrogen Carbonates

Reaction Type: Acid + Hydrogen Carbonate → Salt + Water + CO₂

Example:
Ethanoic acid + Sodium hydrogen carbonate → Sodium ethanoate + Water + CO₂
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

🔸 e) With Alcohols – Esterification Reaction

🔹 4. Detailed: Esterification Reaction

• Carboxylic acid reacts with alcohol in presence of a strong acid catalyst (usually concentrated sulfuric acid) to form an ester and water.

General Equation:
Carboxylic acid + Alcohol ⇌ Ester + Water
(equilibrium reaction)

Example:
Ethanoic acid + Ethanol ⇌ Ethyl ethanoate + Water
CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O

🧪 Conditions:

• Catalyst: Concentrated H₂SO₄
• Heating under reflux

🔹 Esters have sweet, fruity smells.

🔹 5. Uses of Esters

Esters are widely used due to their pleasant smells and chemical properties:

• Perfumes and fragrances
• Food flavourings (like banana essence, pineapple flavour)
• Solvents for paints and nail polish
• Plasticisers in making flexible plastics

📝 Summary Table

>>> Go to the main course

Have Questions? Speak to an Expert: 01817 122800