Class 12 Chemistry Chapter 8: Aldehydes Ketones and Carboxylic Acids Notes for NEET & JEE (PDF + MCQs)
Class 12 Chemistry Chapter 8: Aldehydes, Ketones and Carboxylic Acids | Complete Notes for NEET & JEE
Introduction
Aldehydes, Ketones, and Carboxylic Acids are among the most important oxygen-containing organic compounds studied in Class 12 Chemistry. These compounds are widely used in pharmaceuticals, perfumes, food industries, polymers, dyes, and biological systems.
This chapter introduces the structure, nomenclature, preparation methods, physical properties, chemical reactions, and important named reactions of aldehydes, ketones, and carboxylic acids. It is one of the highest-weightage chapters in Organic Chemistry for NEET, JEE Main, JEE Advanced, and Board Examinations.
Why is This Chapter Important for NEET & JEE?
✅ High-weightage Organic Chemistry chapter
✅ Frequently asked in NEET and JEE
✅ Important named reactions
✅ Conversion-based questions
✅ Direct NCERT questions
✅ Essential for Board Examinations
Download Study Material
📘 Complete Aldehydes, Ketones and Carboxylic Acids Notes PDF
Aldehydes
Aldehydes are organic compounds containing the functional group –CHO.
General Formula
R – CHO
Examples
Methanal (HCHO)
Ethanal (CH₃CHO)
Benzaldehyde (C₆H₅CHO)
Ketones
Ketones contain the carbonyl group (>C=O) bonded to two carbon atoms.
General Formula
R – CO – R'
Examples
Propanone (Acetone)
Butanone
Carboxylic Acids
Carboxylic acids contain the carboxyl functional group (-COOH).
General Formula
R – COOH
Examples
Methanoic Acid (HCOOH)
Ethanoic Acid (CH₃COOH)
Benzoic Acid (C₆H₅COOH)
Nomenclature
Aldehydes
Suffix: -al
Examples:
HCHO → Methanal
CH₃CHO → Ethanal
Ketones
Suffix: -one
Examples:
CH₃COCH₃ → Propanone
CH₃COCH₂CH₃ → Butan-2-one
Carboxylic Acids
Suffix: -oic acid
Examples:
HCOOH → Methanoic Acid
CH₃COOH → Ethanoic Acid
Daily Practice Problems (DPP)
📝 Download Aldehydes, Ketones and Carboxylic Acids DPP
Preparation of Aldehydes
From Primary Alcohols
Controlled oxidation of primary alcohols produces aldehydes.
Example:
Ethanol → Ethanal
Rosenmund Reduction
Acid chlorides are reduced to aldehydes using hydrogen gas and palladium catalyst.
Stephen Reaction
Nitriles are reduced to aldehydes using stannous chloride and hydrochloric acid.
Preparation of Ketones
From Secondary Alcohols
Oxidation of secondary alcohols gives ketones.
Example:
Propan-2-ol → Propanone
Friedel-Crafts Acylation
Benzene reacts with acid chlorides in the presence of AlCl₃.
Preparation of Carboxylic Acids
Oxidation of Primary Alcohols
Primary alcohols are oxidized to carboxylic acids.
Example:
Ethanol → Ethanoic Acid
Oxidation of Aldehydes
Aldehydes are easily oxidized to acids.
Example:
Ethanal → Ethanoic Acid
Physical Properties
Aldehydes and Ketones
✔ Polar molecules
✔ Higher boiling points than hydrocarbons
✔ Lower boiling points than alcohols
✔ Lower members are soluble in water
Carboxylic Acids
✔ Strong intermolecular hydrogen bonding
✔ Higher boiling points
✔ Lower members are soluble in water
Chemical Reactions of Aldehydes and Ketones
Nucleophilic Addition Reactions
Carbonyl carbon is electrophilic and undergoes nucleophilic attack.
Reaction with HCN
Forms cyanohydrins.
Reaction with NaHSO₃
Forms bisulphite addition compounds.
Reaction with Grignard Reagent
Produces alcohols after hydrolysis.
Oxidation Reactions
Aldehydes
Aldehydes are easily oxidized to carboxylic acids.
Ketones
Ketones resist oxidation under mild conditions.
Important Tests
Tollens' Test
Aldehydes give silver mirror.
Observation:
Silver mirror formed.
Fehling's Test
Aliphatic aldehydes produce red precipitate.
Schiff's Test
Aldehydes restore pink colour.
Reduction Reactions
Aldehydes
Reduced to primary alcohols.
Ketones
Reduced to secondary alcohols.
Named Reactions
Aldol Condensation
Aldehydes and ketones containing α-hydrogen undergo condensation.
Cannizzaro Reaction
Aldehydes without α-hydrogen undergo self oxidation-reduction.
Examples:
Formaldehyde
Benzaldehyde
Clemmensen Reduction
Carbonyl group converted into methylene group using Zn-Hg and HCl.
Wolff-Kishner Reduction
Carbonyl group reduced using hydrazine and strong base.
Chemical Reactions of Carboxylic Acids
Acidic Nature
Carboxylic acids are acidic because they release H⁺ ions.
Reaction with Metals
Produces hydrogen gas.
Example:
CH₃COOH + Na → Sodium Acetate + H₂
Esterification
Carboxylic acid reacts with alcohol.
Example:
CH₃COOH + C₂H₅OH → Ethyl Acetate + Water
Catalyst:
Concentrated H₂SO₄
Decarboxylation
Removal of CO₂ from carboxylic acids.
Important Uses
Aldehydes
Preservatives
Perfumes
Resins
Ketones
Solvents
Pharmaceuticals
Carboxylic Acids
Food industry
Vinegar production
Polymer manufacture
Practice Exercises & Assignments
📖 Download Aldehydes, Ketones and Carboxylic Acids Practice Questions
Important Points for Quick Revision
✔ Aldehydes contain -CHO group.
✔ Ketones contain >C=O group.
✔ Carboxylic acids contain -COOH group.
✔ Aldehydes are more reactive than ketones.
✔ Tollens' test gives silver mirror.
✔ Fehling's test identifies aliphatic aldehydes.
✔ Cannizzaro reaction occurs in aldehydes without α-hydrogen.
✔ Aldol condensation requires α-hydrogen.
NEET & JEE Quick Revision
✔ HCHO = Methanal
✔ CH₃CHO = Ethanal
✔ CH₃COCH₃ = Propanone
✔ CH₃COOH = Ethanoic Acid
✔ Tollens' reagent gives silver mirror.
✔ Fehling's solution gives red precipitate.
✔ Cannizzaro reaction occurs without α-hydrogen.
✔ Aldol reaction requires α-hydrogen.
Frequently Asked Questions (FAQs)
Q1. Why are aldehydes more reactive than ketones?
Because aldehydes have less steric hindrance and a greater positive charge on the carbonyl carbon.
Q2. Which tests identify aldehydes?
Tollens' Test
Fehling's Test
Schiff's Test
Q3. Which named reactions are important?
Aldol Condensation
Cannizzaro Reaction
Clemmensen Reduction
Wolff-Kishner Reduction
Q4. Which topics are most important for NEET and JEE?
Carbonyl reactions
Named reactions
Aldehyde tests
Carboxylic acid reactions
Conclusion
Aldehydes, Ketones and Carboxylic Acids form one of the most important chapters in Organic Chemistry. Understanding their preparation, properties, reactions, and named reactions is essential for success in NEET, JEE Main, JEE Advanced, and Board Examinations.
Regular practice of conversion-based questions, reaction mechanisms, and NCERT examples will significantly improve performance in competitive examinations.
Stay connected with Chemistry Achievers Academy for free notes, DPPs, MCQs, PYQs, formula sheets, and chapter-wise study materials for NEET, JEE, CSIR NET, TN SET, and PG TRB examinations.
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