Knowledge Organiser: Carboxylic Acids
Key Terms
- Functional group — -COOH (carboxyl)
- Weak acid — partially dissociates
- General formula — CₙH₂ₙ₊₁COOH
- Formation — oxidise alcohols
First Four Acids
- Methanoic acid — HCOOH (ants)
- Ethanoic acid — CH₃COOH (vinegar)
- Propanoic acid — C₂H₅COOH
- Butanoic acid — C₃H₇COOH (butter)
Key Reactions
- + Metal → salt + H₂
- + Carbonate → salt + H₂O + CO₂ (test!)
- + Alkali → salt + H₂O
- + Alcohol → ester + H₂O (reversible)
Exam Checklist
- Weak acid = partial dissociation, ⇌ symbol
- Carbonate test: fizzing → CO₂ → milky limewater
- Ester formation uses ⇌ (reversible)
- Naming: -anoic acid suffix
Key Equations
- CH₃COOH ⇌ CH₃COO⁻ + H⁺ (ethanoic acid dissociation — weak/partial)
- 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
- CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (esterification)
Common Mistakes
- Saying carboxylic acids are strong acids: They are WEAK acids — they only partially dissociate in water; use ⇌ not → in the dissociation equation
- Forgetting esterification is reversible: Carboxylic acid + alcohol ⇌ ester + water — the ⇌ symbol must be used; writing → loses marks
- Confusing the -COOH and -OH functional groups: Carboxylic acids have -COOH; alcohols have -OH — they are different functional groups with different properties
- Saying no gas is produced with carbonates: Carboxylic acids DO react with carbonates to produce CO₂ (fizzing) — this is the test for carboxylic acids vs alcohols
Memory Aid
- Functional group = -COOH (carboxyl group)
- Naming = same prefix as alkane + "-anoic acid" ending