JEE Main 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. In metallurgy, distinguish roasting from calcination.

   Roasting heats sulphide ore in excess air to form oxides (with SO2 release); calcination heats carbonate/hydrated ore in limited/no air to drive off CO2 or water, giving the oxide.

2. What is the role of a flux and slag in extraction of metals?

   A flux combines with infusible gangue impurities to form a fusible slag, which is easily separated from the molten metal.

3. State Markovnikov's rule for addition of HX to an unsymmetrical alkene.

   The hydrogen of HX adds to the carbon already bearing more hydrogen atoms, and the halogen goes to the more substituted carbon (forming the more stable carbocation).

4. What is the order of stability of carbocations, and why?

   Tertiary > secondary > primary > methyl, because alkyl groups stabilize the positive charge via +I (inductive) effect and hyperconjugation.

5. Define electrophile and nucleophile.

   An electrophile is an electron-pair-deficient (electron-loving) species; a nucleophile is an electron-pair-rich (nucleus-loving) species that donates electrons.

6. In hydrocarbons, what is the peroxide (Kharasch) effect?

   Addition of HBr to alkenes in the presence of peroxides occurs anti-Markovnikov (free-radical mechanism), placing Br on the less substituted carbon.

7. Compare SN1 and SN2 mechanisms in terms of kinetics and stereochemistry.

   SN1: two-step, first-order (rate depends only on substrate), carbocation intermediate, racemization, favoured by 3° substrates. SN2: one-step, second-order, backside attack with inversion of configuration, favoured by 1° substrates.

8. Why are haloarenes less reactive than haloalkanes toward nucleophilic substitution?

   Resonance gives the C–X bond partial double-bond character (shorter, stronger), and sp2 carbon plus repulsion from the ring's pi electrons hinder nucleophilic attack.

9. Define enantiomers and diastereomers.

   Enantiomers are non-superimposable mirror-image stereoisomers (identical physical properties except optical rotation). Diastereomers are stereoisomers that are not mirror images (different physical properties).

10. What is a meso compound?

    A molecule containing chiral (stereo) centres but possessing an internal plane of symmetry, making it optically inactive overall.

11. State the conditions for a compound to show geometrical (cis-trans) isomerism.

    Restricted rotation (e.g., a C=C double bond or ring) and each doubly bonded carbon must carry two different groups.

12. What is the order of acidity: alcohol, water, phenol, and carboxylic acid?

    Carboxylic acid > phenol > water > alcohol. Carboxylate and phenoxide anions are resonance-stabilized, increasing acidity.

13. Why is phenol more acidic than ethanol?

    The phenoxide ion is stabilized by resonance/delocalization of the negative charge into the ring, whereas the ethoxide ion is not, so phenol releases H+ more readily.

14. What is the Williamson ether synthesis?

    Preparation of ethers by reaction of an alkyl halide with a sodium alkoxide (R–O–Na+ + R'–X -> R–O–R' + NaX); an SN2 reaction best done with primary halides.

15. Distinguish aldehydes and ketones using Tollens' test.

    Aldehydes reduce Tollens' reagent (ammoniacal AgNO3) to give a silver mirror; ketones do not (no reaction). It is a test for the –CHO group.

16. What is the Aldol condensation?

    A reaction where an aldehyde/ketone with alpha-hydrogen, under dilute base/acid, gives a beta-hydroxy carbonyl (aldol) that on heating dehydrates to an alpha,beta-unsaturated carbonyl compound.

17. Why are carboxylic acids more acidic than phenols?

    The carboxylate ion is stabilized by resonance over two equivalent oxygen atoms (greater delocalization of charge) than the phenoxide ion, making the carboxylic acid more acidic.

18. What is the Hinsberg test used to distinguish?

    It distinguishes primary, secondary, and tertiary amines using benzenesulphonyl chloride: 1° amines give a base-soluble product, 2° amines give an insoluble product, and 3° amines do not react.

19. What is the product of the carbylamine reaction and what does it test for?

    Primary amines with chloroform and alcoholic KOH give foul-smelling isocyanides (carbylamines). It is a test for primary amines only.

20. Define zwitterion in the context of amino acids.

    A zwitterion is a dipolar ion in which the carboxyl group is deprotonated (–COO^-) and the amino group is protonated (–NH3^+), existing as a net-neutral species (e.g., at the isoelectric point).

21. Distinguish a glycosidic bond from a peptide bond.

    A glycosidic bond links monosaccharide units in carbohydrates (via –O– between sugars); a peptide bond is an amide linkage (–CO–NH–) joining amino acids in proteins.

22. Classify polymers as addition vs condensation with one example each.

    Addition polymers form by repeated addition of monomers without loss of small molecules (e.g., polythene). Condensation polymers form with elimination of small molecules like water (e.g., nylon-6,6).

23. In Chemistry in Everyday Life, what is the difference between antiseptics and disinfectants?

    Antiseptics are applied to living tissue to kill/prevent microbes (e.g., dettol); disinfectants are applied to non-living surfaces (e.g., 1% phenol). The same substance can be either depending on concentration.

24. What are broad-spectrum antibiotics? Give an example.

    Antibiotics effective against a wide range of both Gram-positive and Gram-negative bacteria. Example: chloramphenicol (or tetracycline).

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