Aldehydes, Ketones and Carboxylic Acids

part 1

Aldehydes and Ketones — Preparation

• Nomenclature of aldehydes and ketones
• Preparation from alcohols, alkenes, alkynes
• Preparation using Grignard reagent
• Physical properties

part 2

Reactions of Aldehydes and Ketones

• Nucleophilic addition reactions
• Addition of HCN, NH₂OH, hydrazine, Grignard reagent
• Aldol condensation
• Cannizzaro reaction
• Oxidation and reduction reactions
• Tests to distinguish aldehydes from ketones

part 3

Carboxylic Acids

• Nomenclature and preparation of carboxylic acids
• Physical and chemical properties
• Acidity of carboxylic acids and factors affecting it
• Reactions — with bases, PCl₅, LiAlH₄, decarboxylation
• Uses of carboxylic acids

Aldol condensation

2CH₃CHO → (NaOH) CH₃CH(OH)CH₂CHO → (−H₂O) CH₃CH=CHCHO

★ board favourite

Tollens' test (silver mirror)

RCHO + 2[Ag(NH₃)₂]⁺ → RCOO⁻ + 2Ag↓

★ board favourite

Fehling's test

RCHO + 2Cu²⁺ → RCOO⁻ + Cu₂O↓ (red ppt)

★ board favourite

Iodoform test (methyl ketones)

RCOCH₃ + I₂/NaOH → CHI₃↓ (yellow) + RCOONa

★ board favourite

Nucleophilic addition to C=O

Nu⁻ attacks C of C=O → tetrahedral intermediate → product

★ frequently asked

Cannizzaro reaction (non-enolisable)

2HCHO → (NaOH) CH₃OH + HCOONa

★ frequently asked

Clemmensen reduction

C=O → CH₂ (Zn-Hg/HCl)

★ frequently asked

Wolff-Kishner reduction

C=O → CH₂ (NH₂NH₂/KOH/Δ)

★ frequently asked

Hell-Volhard-Zelinsky (HVZ) reaction

RCOOH + Br₂/(P) → RCH(Br)COOH

★ frequently asked

Give a simple chemical test to distinguish between: (i) acetaldehyde and acetone, (ii) benzaldehyde and acetophenone, (iii) formic acid and acetic acid.

What is the Cannizzaro reaction? Write the reaction of benzaldehyde with concentrated NaOH and name the products formed.

Explain the mechanism of nucleophilic addition of HCN to acetaldehyde. Compare the reactivity of acetaldehyde and acetone towards nucleophilic addition. Give reasons.

Arrange the following in increasing order of acid strength and justify: benzoic acid, 4-nitrobenzoic acid, 4-methoxybenzoic acid, 3,4-dinitrobenzoic acid.

What is aldol condensation? Write the reaction of acetaldehyde undergoing aldol condensation. Under what conditions does cross-aldol condensation occur?

How will you convert: (i) propan-2-ol to propanone, (ii) benzaldehyde to benzoic acid, (iii) acetic acid to acetaldehyde, (iv) toluene to benzaldehyde, (v) ethanal to but-2-enal?

Explain why aldehydes are more reactive than ketones towards nucleophilic addition reactions.

Write the products and name the reaction: (i) benzaldehyde treated with HCHO and NaOH, (ii) acetone treated with dilute Ba(OH)₂, (iii) acetaldehyde treated with Tollens' reagent.

Why is the boiling point of a carboxylic acid higher than that of an alcohol of comparable molecular mass?

(a) Write the mechanism of acid-catalysed nucleophilic addition of an alcohol to acetaldehyde to form an acetal. (b) An organic compound with molecular formula C₃H₆O gives a positive iodoform test but does not reduce Tollens' reagent. Identify the compound and write the reactions.

How many marks is Aldehydes, Ketones and Carboxylic Acids worth in the Class 12 board exam?

Around 8 marks of the 70-mark CBSE Chemistry theory paper, based on the official unit-wise weightage. Aldol condensation, Cannizzaro reaction — name reactions matter.

Is Aldehydes, Ketones and Carboxylic Acids easy or hard?

It's rated hard — one of the tougher chapters in Class 12 Chemistry. Most students need about 5 hours to cover it well.

What are the important topics in Aldehydes, Ketones and Carboxylic Acids?

The chapter covers 14 NCERT topics in 3 areas: Aldehydes and Ketones — Preparation; Reactions of Aldehydes and Ketones; Carboxylic Acids.

What questions come from Aldehydes, Ketones and Carboxylic Acids in board exams?

Between 2018–2024, CBSE board papers asked questions from this chapter on Distinguishing Tests, Cannizzaro Reaction, Nucleophilic Addition, Acidity of Carboxylic Acids — 1- to 5-mark questions.