13.7.6 Carboxylic Acids

This topic explains carboxylic acids — organic compounds containing the carboxyl group (–COOH).

Definition

The functional group of organic acids is called the carboxyl group.

Simple explanation: Carboxylic acids are organic acids that contain the –COOH group.

Main Idea

• Functional group: –COOH (carboxyl group)
• General formula: R–COOH (where R = H or an alkyl group)
• The carboxyl group is a combination of a carbonyl group (C=O) and a hydroxyl group (–OH).

Simple explanation: Carboxylic acids have a –COOH group at the end of a carbon chain.

Core Concept

The Carboxyl Group

–COOH

or

–C(=O)OH

• Carbonyl group (C=O) + Hydroxyl group (–OH)
• This combination gives carboxylic acids their acidic properties.

Simple explanation: The carboxyl group is what makes these compounds acidic.

General Formula

R–COOH

• **R** = H or an alkyl group
• –COOH = carboxyl group

Simple explanation: R–COOH is the general formula for carboxylic acids.

Examples from the Book

Simple explanation: Methanoic acid is the simplest carboxylic acid; ethanoic acid is the main component of vinegar.

The Book's Question

The book asks:

> "What is the difference between a carbonyl group and a carboxyl group?"

• Carbonyl group: C=O (just carbon double-bonded to oxygen)
• Carboxyl group: –COOH (carbonyl group + hydroxyl group)

Simple explanation: A carboxyl group contains a carbonyl group plus an –OH group.

Detailed Explanation

What Makes a Compound a Carboxylic Acid?

• A carbon chain (or H).
• A –COOH group attached.

Examples:

Simple explanation: If it has a –COOH group, it's a carboxylic acid.

Naming Carboxylic Acids

• The alkane name (with -e changed to -oic acid).
• The word "acid" at the end.

Examples:

Simple explanation: Carboxylic acids end in -oic acid.

Homologous Series of Carboxylic Acids

Carboxylic acids form a homologous series with the general formula:

C_nH_2n+1COOH

Simple explanation: Carboxylic acids form a homologous series — each member differs by –CH₂–.

Physical Properties of Carboxylic Acids

Simple explanation: Carboxylic acids have higher boiling points than alcohols because they form stronger hydrogen bonds.

Chemical Properties of Carboxylic Acids

1. Acidic properties: - Carboxylic acids are weak acids. - They ionize in water to produce H⁺ ions: CH₃COOH ⇌ H⁺ + CH₃COO^-

2. Reaction with bases (neutralization): CH₃COOH + NaOH → CH₃COONa + H₂O

3. Reaction with carbonates: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

4. Esterification: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O

Simple explanation: Carboxylic acids behave like acids — they react with bases, carbonates, and alcohols.

Uses of Carboxylic Acids

Simple explanation: Carboxylic acids are used in food, preservation, and industry.

Importance of Ethanoic Acid

• Main component of vinegar (5–8% solution).
• Used to flavour food.
• Used to make polyvinyl acetate (a polymer used in paints and adhesives).
• Used in the production of cellulose acetate (for textiles).

Simple explanation: Ethanoic acid is the acid in vinegar — it has many uses.

Intermediate Level

Structure of Carboxylic Acids

The carboxyl group has:

–C(=O)OH

• A **carbonyl group (C=O)**
• A hydroxyl group (–OH)
• Both attached to the same carbon.

Simple explanation: The carboxyl group is a carbonyl + hydroxyl on the same carbon.

Why Carboxylic Acids Are Acidic

• The –OH in the carboxyl group can lose an H⁺ ion.
• The resulting carboxylate ion (RCOO⁻) is stabilized by resonance.
• This makes carboxylic acids more acidic than alcohols.
• But they are still weak acids (they do not ionize completely).

Simple explanation: Carboxylic acids lose H⁺ easily because the resulting ion is stable.

Comparison with Other Organic Compounds

Simple explanation: Carboxylic acids are the only common organic compounds that react with NaOH and Na₂CO₃.

Reactions of Carboxylic Acids

Simple explanation: Carboxylic acids react with bases, carbonates, and alcohols.

Uses of Carboxylic Acids

Important Points

• - Carboxylic acids: organic compounds containing the carboxyl group (–COOH).
• - Functional group: –COOH.
• - General formula: R–COOH (R = H or alkyl group).
• - Examples:
• - Methanoic acid (formic acid): HCOOH
• - Ethanoic acid (acetic acid): CH₃COOH
• - Naming: ends in -oic acid.
• - Homologous series: CₙH₂ₙ₊₁COOH.
• - Acidity: weak acids — they ionize partially in water.
• - Reactions: with bases, carbonates, and alcohols (esterification).
• - Uses: vinegar, preservatives, plastics, flavorings.

Remember

• - Carboxylic acid = –COOH group.
• - General formula: R–COOH.
• - Naming: ends in -oic acid.
• - Examples:
• - Methanoic acid: HCOOH
• - Ethanoic acid: CH₃COOH (vinegar)
• - Weak acids — ionize partially.
• - React with NaOH, Na₂CO₃, and alcohols.
• - Uses: vinegar, preservatives, plastics, flavorings.

Common Mistakes

• 1. Confusing carboxylic acids with alcohols. Alcohols have –OH; carboxylic acids have –COOH.
• 2. Confusing carboxylic acids with aldehydes. Aldehydes have –CHO; carboxylic acids have –COOH.
• 3. Thinking carboxylic acids are strong acids. They are weak acids.
• 4. Forgetting the carboxyl group contains both C=O and –OH. The carboxyl group is –COOH.
• 5. Thinking carboxylic acids don't react with carbonates. They do react with carbonates, producing CO₂.
• 6. Confusing the naming. Carboxylic acids end in -oic acid (e.g., ethanoic acid).

Quick Revision

• Carboxylic acids: organic compounds containing the carboxyl group (–COOH).
• Functional group: –COOH (carboxyl group).
• General formula: R–COOH (where R = H or alkyl group).
• Examples:
• Methanoic acid (formic acid): HCOOH
• Ethanoic acid (acetic acid): CH₃COOH
• Naming: ends in -oic acid (e.g., methanoic acid, ethanoic acid).
• Homologous series: CₙH₂ₙ₊₁COOH.
• Acidity: weak acids — they ionize partially in water:
• CH₃COOH ⇌ H⁺ + CH₃COO⁻
• Reactions:
• With NaOH → salt + water
• With Na₂CO₃ → salt + water + CO₂
• With alcohols → esters (esterification)
• Uses: vinegar, food flavoring, preservatives, production of plastics.

60-Second Revision

• Carboxylic acid = –COOH group.
• General formula: R–COOH.
• Examples: HCOOH (methanoic acid), CH₃COOH (ethanoic acid).
• Naming: ends in -oic acid.
• Weak acids — react with NaOH and Na₂CO₃.
• Warning: the carboxyl group (–COOH) contains both a carbonyl (C=O) and a hydroxyl (–OH).