Class 12 Chemistry · 3-Mark PYQ Practice

Attempt any 3–5 of these at a time and time yourself (~5–7 min).

1. Explain Kolbe’s reaction with a suitable example and briefly outline the mechanism.
2. Describe Reimer–Tiemann reaction of phenol with mechanism and give one important application.
3. Arrange the following in increasing order of acidity and explain your answer: water, ethanol and phenol.
4. Explain Williamson ether synthesis. Why are aryl halides generally not suitable substrates in this reaction?
5. Distinguish between primary, secondary and tertiary alcohols using any two chemical tests.
6. Explain the oxidation of alcohols using (i) alkaline KMnO₄ and (ii) acidified K₂Cr₂O₇.
7. Explain the acidic nature of phenol on the basis of resonance. Compare it with alcohols.
8. o-Nitrophenol is more volatile than p-nitrophenol. Explain with reason.
9. Explain Pinacol–Pinacolone rearrangement with mechanism.
10. Convert: (i) Propan-1-ol → Propan-2-ol (ii) Phenol → Salicylic acid (Kolbe reaction).
11. How is phenol prepared from (i) diazonium salts and (ii) cumene (cumin hydroperoxide route)?
12. Explain the cleavage of ethers with conc. HI/HBr. Discuss the products with primary, secondary and tertiary alkyl groups.

Focus on mechanisms + “reasoning” questions (order of reactivity, boiling points, etc.).

1. Explain SN1 and SN2 mechanisms of nucleophilic substitution with suitable examples and energy profile diagrams.
2. Why do aryl halides generally not undergo SN1 and SN2 reactions easily? Explain using resonance and bond character.
3. Describe the free radical mechanism for the chlorination of methane in the presence of sunlight.
4. Explain Wurtz reaction and Finkelstein reaction with proper equations.
5. What are ambident nucleophiles? Explain using nitrite ion (NO₂⁻) as an example and give two products formed.
6. How do electron-withdrawing groups like –NO₂ activate aryl halides towards nucleophilic substitution (SNAr)? Explain.
7. Convert: (i) Ethanol → Bromoethane (ii) Chlorobenzene → Phenol (any synthetic route).
8. Explain the competition between elimination and substitution reactions when haloalkanes react with alcoholic KOH.
9. Compare and explain the boiling points of CH₃Cl, CH₃Br and CH₃I.
10. Explain the preparation of chlorobenzene by (i) Sandmeyer reaction and (ii) Gattermann reaction.

Target nucleophilic addition, name reactions and acidity comparisons.

1. Explain the mechanism of nucleophilic addition to a carbonyl group using the addition of HCN to a carbonyl compound as example.
2. Why are aldehydes generally more reactive than ketones towards nucleophilic addition? Give structural reasons.
3. Explain Cannizzaro reaction with mechanism and give one example of each product formed.
4. Describe aldol condensation reaction and show how the product may further undergo dehydration.
5. How can aldehydes and ketones be distinguished using (i) Tollen’s reagent (ii) Fehling’s solution and (iii) Schiff’s reagent?
6. Explain the acidic strength of carboxylic acids on the basis of resonance stabilization of the carboxylate ion.
7. Formic acid is stronger than acetic acid. Explain on the basis of inductive effect.
8. Write a short note on Hell–Volhard–Zelinsky (HVZ) reaction of carboxylic acids with suitable example.
9. Convert: (i) Ethanal → Ethanoic acid (ii) Acetone → tert-Butyl alcohol (using appropriate reagents).
10. Explain the formation of (i) cyanohydrins and (ii) bisulphite addition compounds of aldehydes and ketones.
11. Explain Clemmensen reduction and Wolff–Kishner reduction of carbonyl compounds with conditions.
12. Describe esterification of carboxylic acids and hydrolysis of esters under acidic and basic conditions.

Revise basicity order, tests, and the three main preparations (Gabriel, Hofmann, nitro reduction).

1. Distinguish between primary, secondary and tertiary amines using Hinsberg’s test. Explain the observations.
2. Explain Gabriel phthalimide synthesis for the preparation of primary amines with mechanism.
3. Explain Hofmann bromamide reaction with mechanism. What type of amine is obtained?
4. Discuss the basicity order of NH₃, RNH₂, R₂NH and R₃N in (i) gas phase and (ii) aqueous solution.
5. Explain the preparation of amines by reduction of (i) nitro compounds and (ii) nitriles.
6. Describe diazotisation of aromatic primary amines. Mention the conditions required for the reaction.
7. Explain coupling reactions of benzene diazonium chloride with phenol and aniline.
8. Convert: (i) Nitrobenzene → Aniline (ii) Aniline → p-Bromoaniline.
9. Why are aryl amines less basic than alkyl amines? Explain using resonance and inductive effects.
10. Write a note on the carbylamine reaction of primary amines with suitable equation.

Concentrate on definitions + 2–3 examples and neat labeled sketches where possible.

1. Distinguish between reducing and non-reducing sugars. Give one example of each.
2. Explain mutarotation of glucose. How does it support the cyclic structure of glucose?
3. Describe the structure of α-D(+)-glucose and β-D(+)-glucose using Haworth projection formulae.
4. Explain denaturation of proteins. What changes occur in their properties on denaturation?
5. Describe the primary, secondary and tertiary structure of proteins.
6. How is a peptide bond formed between amino acids? Explain with example.
7. What are essential and non-essential amino acids? Give two examples of each.
8. Differentiate between oils and fats. Explain iodine value and saponification value briefly.
9. Classify vitamins into fat-soluble and water-soluble types with at least one example of each.
10. Write short notes on (i) nucleosides (ii) nucleotides and (iii) nucleic acids.
11. Explain the zwitterion structure of α-amino acids. How does it affect their physical properties?
12. Describe enzymes as biocatalysts. Mention their specificity and conditions under which they act.