CBSE Class 12 Board Exam Chemistry Flashcards

24 sample cards from the Chemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. How is the acidity of phenol explained compared to alcohols?

   Phenol is more acidic because the phenoxide ion formed on losing H⁺ is resonance-stabilized (negative charge delocalized into the ring), whereas alkoxide ions are not.

2. What is the Williamson ether synthesis?

   An ether is prepared by the SN2 reaction of a sodium alkoxide with a primary alkyl halide: R–O⁻Na⁺ + R'–X → R–O–R' + NaX.

3. What is Kolbe's reaction (Kolbe's carboxylation)?

   Sodium phenoxide reacts with CO₂ under pressure followed by acidification to give salicylic acid (2-hydroxybenzoic acid).

4. Name the reaction: phenol + CHCl₃ + NaOH → salicylaldehyde.

   Reimer–Tiemann reaction.

5. How are primary, secondary, and tertiary alcohols distinguished by the Lucas test?

   With Lucas reagent (conc. HCl + ZnCl₂): tertiary alcohols give immediate turbidity, secondary give turbidity in ~5 minutes, and primary give no turbidity at room temperature.

6. What is the Cannizzaro reaction?

   Aldehydes lacking an α-hydrogen, when treated with concentrated alkali, undergo disproportionation: one molecule is oxidized to a carboxylate and another reduced to an alcohol.

7. State the test that distinguishes aldehydes from ketones using Tollens' reagent.

   Aldehydes reduce Tollens' reagent (ammoniacal AgNO₃) to give a silver mirror; ketones do not react. This is the silver-mirror test.

8. What is the aldol condensation reaction?

   Aldehydes/ketones with α-hydrogen, in dilute base, combine to form a β-hydroxy aldehyde/ketone (aldol), which on heating loses water to give an α,β-unsaturated carbonyl compound.

9. Why are carboxylic acids more acidic than phenols?

   Because the carboxylate ion is stabilized by resonance over two equivalent oxygen atoms (greater delocalization), making the carboxylic acid release H⁺ more readily than phenol.

10. What is the HVZ (Hell–Volhard–Zelinsky) reaction?

    Carboxylic acids having an α-hydrogen react with Cl₂/Br₂ in the presence of red phosphorus to give α-halocarboxylic acids.

11. How are amines classified as primary, secondary, and tertiary?

    By the number of hydrogen atoms of ammonia replaced by alkyl/aryl groups: primary (RNH₂, one), secondary (R₂NH, two), tertiary (R₃N, three).

12. Why are aliphatic amines more basic than ammonia, while aromatic amines (aniline) are less basic?

    Alkyl groups are electron-donating, increasing electron density on N (more basic). In aniline, the lone pair on N is delocalized into the ring, reducing availability for protonation (less basic).

13. What is the carbylamine reaction and what does it test for?

    Primary amines heated with chloroform and alcoholic KOH give foul-smelling isocyanides (carbylamines). It is a test for primary amines (secondary and tertiary do not respond).

14. What is Hofmann's bromamide degradation reaction?

    A primary amide treated with Br₂ and aqueous/alcoholic NaOH (KOH) gives a primary amine with one fewer carbon atom: R–CONH₂ → R–NH₂.

15. What happens when aniline reacts with NaNO₂ and HCl at 0–5 °C?

    It forms benzenediazonium chloride (diazotisation): C₆H₅NH₂ → C₆H₅N₂⁺Cl⁻.

16. Classify carbohydrates into the three main groups with one example each.

    Monosaccharides (e.g., glucose), oligosaccharides such as disaccharides (e.g., sucrose), and polysaccharides (e.g., starch).

17. What is the difference between a reducing and a non-reducing sugar? Give an example of each.

    Reducing sugars have a free aldehyde/ketone group and reduce Tollens'/Fehling's reagent (e.g., glucose, maltose). Non-reducing sugars do not (e.g., sucrose).

18. What are essential and non-essential amino acids?

    Essential amino acids cannot be synthesized by the body and must be obtained from diet; non-essential amino acids can be synthesized by the body.

19. What is the difference between DNA and RNA in terms of sugar and bases?

    DNA contains deoxyribose sugar and bases A, T, G, C; RNA contains ribose sugar and bases A, U (uracil instead of thymine), G, C.

20. Define the primary and secondary structure of proteins.

    Primary structure is the specific sequence of amino acids linked by peptide bonds. Secondary structure is the local folding (α-helix or β-pleated sheet) stabilized by hydrogen bonds.

21. What is denaturation of a protein?

    The loss of the native secondary and tertiary structure (by heat, acid, etc.) while the primary structure remains intact, causing loss of biological activity (e.g., coagulation of egg white).

22. In qualitative organic analysis, how is nitrogen detected (Lassaigne's test)?

    In Lassaigne's extract, sodium fusion converts N to NaCN; adding FeSO₄ then Fe³⁺ and acid gives a Prussian blue colour, confirming nitrogen.

23. How are sulphur and the unsaturation (C=C) of an organic compound detected in functional-group tests?

    Sulphur: Lassaigne's extract gives violet colour with sodium nitroprusside (or black PbS with lead acetate). Unsaturation: decolourization of bromine water or pink KMnO₄ (Baeyer's reagent).

24. What is the iodoform test and which groups give a positive result?

    Treatment with I₂/NaOH gives a yellow precipitate of iodoform (CHI₃). Positive for compounds containing CH₃CO– (methyl ketones) or CH₃CH(OH)– groups, and ethanol/acetaldehyde.

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