Karnataka 2nd PUC Chemistry: Aldehydes, Ketones and Carboxylic Acids 2M, 3M & 5M Questions

Aldehydes, Ketones and Carboxylic Acids is an important chapter in the Karnataka 2nd PUC Chemistry syllabus. It covers the properties and reactions of carbonyl compounds, preparation methods, named reactions and chemical tests used to identify different functional groups.

For exam preparation, students should pay particular attention to named reactions such as Wolff-Kishner reduction, Rosenmund reduction, Aldol condensation, Cannizzaro reaction and the Hell-Volhard-Zelinsky reaction. Organic conversions, reaction mechanisms and differences between aldehydes and ketones are also useful areas to practise.

The following questions and 2nd PUC Chemistry Previous Year Question Paper cover key concepts from the chapter and can help students prepare for 2-mark, 3-mark and 5-mark questions.

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Karnataka 2nd PUC Chemistry: Important 2 Marks Questions

Practise these short-answer questions to revise definitions, reagents, products and basic reaction concepts.

1. What is the Hell-Volhard-Zelinsky (HVZ) reaction? Write its general reaction.

2. What is the Wolff-Kishner reduction?

3. Name the reagent used in the Rosenmund reduction.

4. What happens when an aldehyde reacts with hydroxylamine?

5. What is a cyanohydrin? How is it formed?

6. Why does benzaldehyde not undergo Aldol condensation?

7. Which test is used to distinguish aldehydes from ketones?

8. What happens when a carboxylic acid reacts with PCl₅?

9. What is the product formed when a carbonyl compound reacts with hydrazine?

10. Why do ketones generally not give Tollens' test?

2nd PUC Chemistry Named Reactions You MUST Know

Karnataka 2nd PUC Chemistry: Important 3 Marks Questions

These 2nd PUC Chemistry important questions focus on explaining reactions, writing chemical equations and comparing the behaviour of organic compounds.

1. Explain the Rosenmund reduction with a chemical equation.

2. Explain the Wolff-Kishner reduction with a suitable example.

3. Write the chemical equation for the Gattermann-Koch reaction.

4. Explain the Hell-Volhard-Zelinsky reaction with an example.

5. Differentiate between Aldol condensation and the Cannizzaro reaction based on the presence of alpha-hydrogen.

6. Explain how aldehydes and ketones react with hydroxylamine to form oximes.

7. How can acetaldehyde and acetone be distinguished using Tollens' and Fehling's tests?

8. Explain the reaction of carboxylic acids with PCl₅.

9. How is benzamide prepared from benzoic acid?

10. Explain the formation of cyanohydrins from aldehydes and ketones.

Karnataka 2nd PUC Chemistry: Important 5 Marks Questions

Long-answer questions from this chapter may require students to explain reaction steps, write balanced equations or discuss the chemical behaviour of compounds.

1. Explain Aldol condensation with a suitable example. Write the chemical equation and mention the role of alpha-hydrogen.

2. Explain the Cannizzaro reaction with an example. Why does benzaldehyde undergo this reaction?

3. Describe the Wolff-Kishner reduction and Rosenmund reduction with suitable chemical equations.

4. Explain the Tollens' test and Fehling's test. How are these tests used to distinguish aldehydes from ketones?

5. Explain the Hell-Volhard-Zelinsky reaction and write its general chemical equation.

6. Describe the nucleophilic addition reactions of aldehydes and ketones with HCN and hydroxylamine.

7. Explain the following organic conversions with suitable reagents:

• Benzoic acid to benzamide

• Benzene to benzaldehyde

• Acetyl chloride to acetaldehyde

8. Explain the important reactions of aldehydes and ketones with nitrogen-containing reagents.

Note: These are chapter-based practice questions prepared from the concepts covered below. They are not an officially released or guaranteed examination question list.

Important Named Reactions from Aldehydes, Ketones and Carboxylic Acids

Named reactions are useful for both short-answer and descriptive questions. Students should learn the reaction conditions, reagents and final products rather than memorising only the reaction names.

1. Wolff-Kishner Reduction

In the Wolff-Kishner reduction, aldehydes and ketones are converted into hydrocarbons. The carbonyl compound first reacts with hydrazine (NH₂NH₂) to form a hydrazone. On heating with KOH in a high-boiling solvent such as ethylene glycol, the hydrazone gives a hydrocarbon with the release of nitrogen gas.

General reaction:

R₂C=O → R₂C=NNH₂ → R₂CH₂

2. Rosenmund Reduction

Rosenmund reduction is used to prepare aldehydes from acid chlorides. The acid chloride is hydrogenated using palladium supported on barium sulfate (Pd/BaSO₄), with the catalyst partially poisoned to prevent further reduction.

General reaction:

RCOCl + H₂ → RCHO + HCl

3. Gattermann-Koch Reaction

In the Gattermann-Koch reaction, benzene reacts with carbon monoxide and hydrogen chloride in the presence of anhydrous AlCl₃ and cuprous chloride to form benzaldehyde.

Reagents: CO + HCl, anhydrous AlCl₃ and CuCl.

4. Hell-Volhard-Zelinsky Reaction

Carboxylic acids containing an alpha-hydrogen undergo halogenation at the alpha-carbon when treated with chlorine or bromine in the presence of red phosphorus.

General reaction:

R–CH₂–COOH + X₂ → R–CHX–COOH

Here, X represents chlorine or bromine. The reaction is followed by hydrolysis.

5. Aldol Condensation

Aldehydes and ketones containing at least one alpha-hydrogen undergo Aldol condensation in the presence of dilute alkali. The reaction initially produces a beta-hydroxy aldehyde or ketone. On heating, the product may lose water to form an alpha,beta-unsaturated carbonyl compound.

For example, two molecules of acetaldehyde react in dilute NaOH to form 3-hydroxybutanal, which can dehydrate on heating.

6. Cannizzaro Reaction

Aldehydes that do not contain alpha-hydrogen undergo the Cannizzaro reaction in the presence of concentrated alkali. One molecule of aldehyde is oxidised to a carboxylate salt, while another is reduced to an alcohol.

Benzaldehyde and formaldehyde are common examples of aldehydes that undergo this reaction.

Karnataka 2nd PUC Chemistry Model Paper 2026-27

Aldol Condensation vs Cannizzaro Reaction

The presence or absence of alpha-hydrogen determines whether an aldehyde or ketone can undergo Aldol condensation or the Cannizzaro reaction.

Important exam point: Benzaldehyde does not undergo Aldol condensation because it has no alpha-hydrogen. It undergoes the Cannizzaro reaction in the presence of concentrated alkali.

Important Chemical Tests: Aldehydes vs Ketones

Chemical tests help identify aldehydes and distinguish them from ketones. Students should remember the reagent, observation and inference for each test.

Tollens' Test

Tollens' reagent is ammoniacal silver nitrate. When an aldehyde is warmed with this reagent, silver ions are reduced to metallic silver, producing a silver mirror on the inner surface of the test tube.

Ketones generally do not give this reaction.

Fehling's Test

When an aliphatic aldehyde is heated with Fehling's solution, a brick-red precipitate of cuprous oxide (Cu₂O) is formed. Ketones and aromatic aldehydes generally do not give this test.

Important Organic Conversions to Practise

Organic conversions require students to identify the starting compound, select the correct reagent and write the final product. Practise the following conversions:

Preparation of benzamide from benzoic acid: Benzoic acid reacts with ammonia to form ammonium benzoate. On heating, ammonium benzoate undergoes dehydration to form benzamide.

Preparation Tips for This Chemistry Chapter

A focused revision plan can help students prepare the chapter more effectively:

• Revise named reactions: Learn the reagents, reaction conditions and products of Rosenmund reduction, Wolff-Kishner reduction, Gattermann-Koch reaction and HVZ reaction.

• Practise organic conversions: Write each conversion step by step and check whether the reagents are correct.

• Understand alpha-hydrogen: Revise why compounds such as acetaldehyde undergo Aldol condensation, while benzaldehyde undergoes the Cannizzaro reaction.

• Learn chemical tests: Remember the observations for Tollens' and Fehling's tests.

• Write balanced equations: Include the correct reactants, reagents and products in descriptive answers.

• Practise different question formats: Revise definitions, reaction-based questions, distinctions and longer explanations.

Students should also check the Karnataka 2nd PUC Time Table 2027 to stay updated on subject-wise examination dates, exam schedules, and important instructions for the upcoming Karnataka Class 12 board examinations.