CBSE Class 12 Chemistry Chapter 9 Amines — 20 MCQs with Answers

Amines are classified based on the number of carbon atoms directly bonded to the nitrogen atom. A primary amine has one alkyl or aryl group (RNH₂), a secondary amine has two (R₂NH), and a tertiary amine has three (R₃N). IUPAC names use the suffix '-amine' with the longest carbon chain as the parent. Common names list alkyl groups alphabetically followed by '-amine'. Aromatic amines like aniline, N-methylaniline, and N,N-dimethylaniline are named with 'aniline' as the base. Understanding these distinctions is critical because reactivity (especially towards acylation and sulphonation) varies sharply among the three classes. NCERT Class 12 Chemistry MCQ questions often test your ability to identify the class of an amine from a given structure or IUPAC name.

Amines can be prepared by reduction of nitro compounds, nitriles, and amides, or by nucleophilic substitution (alkylation of ammonia). The Gabriel phthalimide synthesis is a specific and elegant method for preparing pure primary aliphatic amines. In this method, phthalimide reacts with alcoholic KOH to form potassium phthalimide, which then undergoes nucleophilic substitution with an alkyl halide (preferably primary) to give N-alkyl phthalimide. Hydrolysis with aqueous NaOH or hydrazine (Gabriel reaction modification) releases the primary amine. This method avoids over-alkylation and is not suitable for aromatic amines because aryl halides do not undergo nucleophilic substitution under these conditions. CBSE Class 12 Chemistry chapter 9 quiz frequently includes MCQs on the scope and limitations of this synthesis.

Reduction of nitro compounds is a versatile method for preparing both aliphatic and aromatic amines. Aromatic nitro compounds like nitrobenzene are reduced to aniline using Sn/HCl or Fe/HCl followed by neutralisation. Aliphatic nitroalkanes are reduced using LiAlH₄ or catalytic hydrogenation (H₂/Ni). Nitriles (R–C≡N) can be reduced to primary amines using LiAlH₄ or H₂/Ni, yielding an amine with one more carbon atom than the original nitrile. Amides can also be reduced to amines using LiAlH₄, producing amines with the same carbon count as the amide. These methods are staple questions in Class 12 Chemistry Amines multiple choice sets because they test understanding of reagent selection and the relationship between functional groups and product structure.

Amines exhibit hydrogen bonding due to the presence of a lone pair on nitrogen. Primary and secondary amines can form intermolecular H-bonds, resulting in higher boiling points than hydrocarbons of similar molecular mass. Tertiary amines cannot donate a hydrogen for H-bonding, so their boiling points are lower than corresponding 1° or 2° amines. Amines are basic because the lone pair on nitrogen can accept a proton. Aliphatic amines are generally more basic than ammonia due to the +I effect of alkyl groups, which increases electron density on nitrogen. Aromatic amines like aniline are weaker bases than ammonia because the lone pair on nitrogen is delocalised into the benzene ring by resonance, reducing its availability for protonation. NCERT Class 12 Chemistry MCQ questions often compare the basicity order of different amines or ask you to explain trends in boiling points.

The carbylamine test is a qualitative test specific for primary amines. When a primary amine (aliphatic or aromatic) is heated with chloroform (CHCl₃) and alcoholic KOH, it forms an isocyanide (carbylamine) with a characteristic offensive smell. Secondary and tertiary amines do not give this test. The Hinsberg test uses benzenesulphonyl chloride (C₆H₅SO₂Cl) to distinguish among 1°, 2°, and 3° amines. A primary amine reacts to form N-alkylbenzenesulphonamide, which is soluble in aqueous KOH (due to acidic N–H). A secondary amine forms a sulphonamide that is insoluble in KOH (no acidic H). A tertiary amine does not react at all with Hinsberg reagent. These tests are high-yield for Amines important questions Class 12 and appear regularly in board MCQs and short-answer sections.

Diazonium salts have the general formula Ar–N₂⁺X⁻ and are prepared by the diazotisation of aromatic primary amines with nitrous acid (NaNO₂ + HCl) at 0-5°C. The reaction must be carried out at low temperature because diazonium salts are highly unstable above 5°C and decompose explosively. Aliphatic diazonium salts are even more unstable and decompose immediately at room temperature, so only aromatic diazonium salts are practically useful. The nitrogen molecule (N₂) is an excellent leaving group, making diazonium salts versatile intermediates for introducing various functional groups (–OH, –Cl, –Br, –I, –CN, –F, –H) onto the benzene ring via Sandmeyer, Gattermann, or Balz-Schiemann reactions. CBSE Class 12 Chemistry chapter 9 quiz questions test both the conditions of diazotisation and the rationale behind temperature control.

Diazonium salts undergo two main types of reactions: replacement reactions (where N₂ is replaced by another group) and coupling reactions (where the diazonium ion acts as an electrophile). In Sandmeyer reactions, diazonium salts react with CuCl, CuBr, or CuCN to introduce –Cl, –Br, or –CN groups respectively. The Gattermann reaction uses Cu powder with HCl or HBr. To introduce –F, the Balz-Schiemann reaction treats the diazonium salt with HBF₄, then heats the resulting diazonium fluoroborate. For hydroxyl groups, diazonium salts are warmed with water. Azo coupling occurs when diazonium salts react with phenols or aromatic amines in mildly alkaline solution, forming brightly coloured azo dyes (Ar–N=N–Ar'). These reactions are heavily tested in Class 12 Chemistry Amines multiple choice questions, especially in application and case-based formats, because they showcase the synthetic utility of diazonium chemistry in industrial dye manufacture.

In the 2025 CBSE Class 12 Chemistry board exam, Section A typically contains 16 MCQs of 1 mark each. Four of these are assertion-reason type. For Chapter 9 Amines, expect one MCQ on nomenclature or classification, one on preparation methods (Gabriel or reduction), one on tests (carbylamine or Hinsberg), and one on diazonium salts or their reactions. Read each question twice before marking. Eliminate obviously wrong options first. For assertion-reason MCQs, evaluate the assertion and reason independently, then check if the reason correctly explains the assertion. Watch for subtle differences: for example, Gabriel synthesis works only for aliphatic amines, not aromatic. Time management is crucial: allocate 20 minutes for all 16 MCQs, leaving ample time for the long-answer section. If unsure, flag the question and return after completing the rest. Never leave an MCQ unattempted — there is no negative marking in CBSE. Practice with previous years' question papers and NCERT exemplar problems. CBSETUTOR.ai offers a 24×7 AI tutor where you can upload photos of MCQ sets, get instant explanations, and clarify doubts on the spot at a flat ₹999/month for all classes 6-12, with a 3-day free trial. Regular practice sharpens pattern recognition and boosts speed, both essential for scoring full marks in Section A.