ISC Class 12 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. What is the role of an Ellingham diagram in metal extraction?

   It plots the standard Gibbs free energy of formation (ΔG°) of oxides versus temperature, helping select a suitable reducing agent and the temperature at which reduction becomes thermodynamically feasible (ΔG° negative).

2. Name the methods of refining metals.

   Distillation (low boiling metals like Zn, Hg), liquation (Sn), electrolytic refining (Cu, Al), zone refining (Si, Ge—ultra pure), vapour phase refining (Mond process for Ni, van Arkel for Zr/Ti), and chromatography.

3. List the general trends of Group 15 elements (oxidation states and hydrides).

   Common oxidation states are −3, +3, +5; stability of +5 decreases and +3 increases down the group (inert pair effect). Hydrides (NH3, PH3, AsH3, SbH3, BiH3) show decreasing thermal stability and basicity down the group; NH3 is most basic.

4. Describe the trends in oxides and hydrides of Group 16 elements.

   Oxidation states −2, +2, +4, +6; acidic character of dioxides increases down the group then... actually SO2>SeO2>TeO2 in acidity decreasing. Hydrides H2O, H2S, H2Se, H2Te, H2Po show decreasing thermal stability and increasing acidic/reducing character down the group; H2O has anomalously high boiling point due to H-bonding.

5. What are the trends in Group 17 (halogen) elements regarding reactivity and oxidising power?

   Halogens are highly reactive non-metals; reactivity and oxidising power decrease down the group (F2 > Cl2 > Br2 > I2). Electronegativity decreases, bond dissociation enthalpy is highest for Cl2 (F2 anomalously low), and they show −1 oxidation state plus positive states (except F).

6. Why are Group 18 elements called noble (inert) gases, and which form compounds?

   They have completely filled valence shells (ns²np⁶, except He = 1s²), making them chemically inert. Xenon forms compounds with fluorine and oxygen (e.g., XeF2, XeF4, XeF6, XeO3) due to its low ionisation enthalpy; Kr forms KrF2.

7. What is a transition element, and why are Sc and Zn sometimes not considered typical transition metals?

   A transition element has a partially filled d-subshell in its atom or in a common ion. Sc (and Zn) are not typical: Zn²⁺ (3d¹⁰) has a full d-subshell, and Sc³⁺ (3d⁰) is empty, so they don't show characteristic transition properties like variable valency or coloured ions.

8. List four characteristic properties of transition elements.

   Variable oxidation states, formation of coloured ions/compounds, paramagnetism (unpaired d-electrons), catalytic activity, formation of complex/coordination compounds, and formation of interstitial compounds and alloys.

9. What are inner transition elements? Name the two series.

   Elements in which the last electron enters the (n−2)f orbital (f-block). The two series are the lanthanoids (4f, Ce–Lu) and the actinoids (5f, Th–Lr).

10. What is the lanthanoid contraction and one of its consequences?

    The steady decrease in atomic and ionic radii of lanthanoids with increasing atomic number due to poor shielding by 4f electrons. A consequence is the similarity in size of second and third transition series elements (e.g., Zr and Hf).

11. What is a ligand? Classify ligands by their denticity.

    A ligand is an ion or molecule that donates a lone pair of electrons to a central metal atom/ion. By denticity: monodentate (one donor, e.g., NH3, Cl⁻), bidentate (two donors, e.g., ethylenediamine, oxalate), polydentate/chelating (e.g., EDTA, hexadentate), and ambidentate (can bind through different atoms, e.g., NO2⁻/ONO⁻).

12. Define coordination number of a central metal atom in a complex.

    The number of ligand donor atoms (sigma bonds) directly bonded to the central metal atom/ion. For example, in [Co(NH3)6]³⁺ the coordination number is 6.

13. What does Werner's coordination theory state about primary and secondary valencies?

    Metals show two types of valencies: primary valency (ionisable, satisfied by negative ions, = oxidation state) and secondary valency (non-ionisable, satisfied by ligands, = coordination number, and gives the complex its definite geometry).

14. State the basic IUPAC nomenclature rules for naming coordination compounds.

    Name ligands alphabetically before the metal; anionic ligands end in -o, neutral keep their names; use prefixes di/tri or bis/tris; the cation is named first; in anionic complexes the metal ends in -ate; the metal's oxidation state is given in Roman numerals in parentheses.

15. Describe the nature of the C–X bond in haloalkanes.

    The C–X bond is polar because the halogen is more electronegative than carbon, giving carbon a partial positive (δ+) and halogen a partial negative (δ−) charge. Bond length increases and bond strength decreases from C–F to C–I.

16. Compare SN1 and SN2 mechanisms of nucleophilic substitution.

    SN1 is two-step via a carbocation intermediate, first-order kinetics, favoured by tertiary halides and polar protic solvents, gives racemisation. SN2 is one-step concerted, second-order kinetics, favoured by primary halides and polar aprotic solvents, gives inversion of configuration (Walden inversion).

17. How are alcohols classified, and give the general nomenclature suffix.

    Classified as primary, secondary, or tertiary based on the carbon bearing the –OH group, and as mono-, di-, or trihydric by number of –OH groups. IUPAC suffix is -ol (e.g., ethanol).

18. State two properties/reactions distinguishing phenols from alcohols.

    Phenols are acidic (turn blue litmus... react with NaOH to form salts) due to resonance stabilisation of the phenoxide ion, whereas alcohols are neutral; phenol gives a violet colour with neutral FeCl3, alcohols do not.

19. Describe the structure of the carbonyl group in aldehydes and ketones.

    The carbonyl carbon is sp² hybridised with a planar trigonal geometry; the C=O consists of a sigma bond and a pi bond, and is polar (Cδ+=Oδ−), making the carbon electrophilic and susceptible to nucleophilic addition.

20. How are amines classified and named?

    By the number of H atoms of ammonia replaced: primary (RNH2), secondary (R2NH), tertiary (R3N). Named as alkanamines (IUPAC) or alkylamines; basicity arises from the lone pair on nitrogen.

21. What are the products and conditions of the diazotisation reaction?

    Primary aromatic amines react with nitrous acid (NaNO2 + HCl) at 0–5 °C to form arenediazonium salts (e.g., benzenediazonium chloride), which are useful synthetic intermediates for substitution and coupling (azo dye) reactions.

22. Classify carbohydrates and give one example of each major class.

    Monosaccharides (glucose, fructose—cannot be hydrolysed), oligosaccharides such as disaccharides (sucrose, maltose, lactose), and polysaccharides (starch, cellulose, glycogen). Also reducing vs non-reducing sugars (sucrose is non-reducing).

23. What are the four levels of protein structure and what holds proteins together?

    Primary (sequence of amino acids, peptide bonds), secondary (α-helix/β-pleated sheet via H-bonds), tertiary (overall 3D folding via various bonds), and quaternary (assembly of subunits). Denaturation destroys secondary/tertiary structure.

24. What is the difference between addition and condensation polymers? Give examples.

    Addition polymers form by repeated addition of monomers with no loss of molecules (e.g., polythene, PVC, Teflon); condensation polymers form by repeated condensation with elimination of small molecules like water (e.g., nylon-6,6, terylene/dacron, bakelite). Biodegradable examples include PHBV and nylon-2-nylon-6.

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