1. Metallurgy

What is the difference between minerals and ores? May/2022, Mar/2024
S.No Minerals Ores
1 Naturally occurring substances obtained by mining which contain the metals in free state or in the form of compounds like oxides, sulphides etc. Minerals that contain a high percentage of metal from which it can be extracted conveniently and economically.
2 All minerals are not ores. All ores are minerals.
3 Minerals of Al are Bauxite and Clay. Ore of Al is Bauxite.
What are the various steps involved in extraction of pure metals from their ores?
  • (i) Concentration of the ore
  • (ii) Extraction of crude metal
  • (iii) Refining of crude metal
What is the role of limestone in the extraction of iron from its oxide Fe₂O₃? Jun/2020
Limestone (CaCO₃) is used as a basic flux. It decomposes to form CaO:
CaCO₃ → CaO + CO₂
The impurity silica (SiO₂) reacts with CaO to form fusible slag calcium silicate:
CaO + SiO₂ → CaSiO₃
Which type of ores can be concentrated by froth flotation method? Give two examples. Jun/2020, Apr/2023, Mar/2025
Sulphide ores can be concentrated by froth flotation method.
Examples: Galena (PbS) and Zinc blende (ZnS).
Describe a method for refining nickel. May/2022, June/2023, Mar/2025
Nickel is refined by Mond's process. Impure nickel is heated in a stream of carbon monoxide at around 350K to form highly volatile nickel tetracarbonyl:
Ni(s) + 4CO(g) → Ni[CO]₄(g) [at 350K]
On further heating the volatile vapour decomposes to give pure nickel:
Ni[CO]₄(g) → Ni(s) + 4CO(g)
Explain zone refining process with an example. Mar/2020, Apr/2023
  • This method is based on the principle of fractional crystallisation.
  • The impure metal is taken in the form of a rod and heated with a mobile heater, melting the zone.
  • The impurities dissolve more smoothly in the molten zone, moving along with the heater away from the pure metal.
  • The process is carried out in an inert gas atmosphere to prevent metal oxidation.
  • Examples: Germanium, Silicon, and Gallium used as semiconductors.

2. p-Block Elements - I

Write a short note on anomalous properties of the first element of p-block. Sept/2020, Aug/2021
  • Small atomic size
  • High ionisation enthalpy and high electronegativity
  • Absence of d-orbitals in their valence shell
What is catenation? Describe briefly the conditions of catenation. Mar/2020, Sept/2020, Sept/2022
Catenation is the ability of an element to form a long chain of atoms linked with itself.
Conditions:
  • The valency of the element must be greater than or equal to two.
  • The element should have an ability to bond with itself.
  • The self-bond must be strong.
  • Kinetic inertness of the catenated compound.
Why AlCl₃ acts as a Lewis acid?
AlCl₃ is an electron-deficient compound. Therefore, it acts as an electron pair acceptor (Lewis acid).
Write the Ethyl borate test. Apr/2023, Mar/2025
When borates are heated with concentrated H₂SO₄ and ethanol, triethyl borate ester is formed. When the vapours are exposed to a flame, it burns with a characteristic green-edged flame:
H₃BO₃ + 3C₂H₅OH → B(OC₂H₅)₃ + 3H₂O [in presence of Conc. H₂SO₄]

3. p-Block Elements - II

What is the inert pair effect? May/2022
As we move down a group in the p-block elements, the outer ns² electrons become inert and show reluctance to involve themselves in chemical combination. Only the outer np electrons take part in bonding. This phenomenon is known as the inert pair effect.
What are interhalogen compounds? Give examples. Aug/2021, May/2022
Each halogen combines with other halogens to form a series of binary compounds called interhalogen compounds.
Examples: ClF, BrF₃, BrF₅, IF₇.
Why HF cannot be stored in glass bottles? Mar/2020
Moist hydrofluoric acid (HF) rapidly reacts with sodium silicate present in the glass, corroding it:
Na₂SiO₃ + 6HF → Na₂SiF₆ + 3H₂O

4. Transition and Inner Transition Elements

What are interstitial compounds? Sept/2020, Aug/2021, June/2023
An interstitial compound is formed when small atoms like hydrogen, boron, carbon, or nitrogen are trapped inside the interstitial interstitial holes or voids of a transition metal lattice. They are usually non-stoichiometric.
Examples: TiC, Mn₄N.
Among Fe²⁺ and Fe³⁺, which one is more stable and why? May/2022, Mar/2024
  • Electronic configuration of Fe²⁺ = [Ar] 3d⁶
  • Electronic configuration of Fe³⁺ = [Ar] 3d⁵
Fe³⁺ is more stable than Fe²⁺ because it possesses a symmetric, completely half-filled d-orbital (3d⁵) configuration.
What is Lanthanoid contraction? List its consequences. Jun/2020, June/2023, Mar/2024
As we move across the 4f lanthanoid series, the atomic and ionic radii show a gradual decrease with an increase in atomic number. This regular decrease is called Lanthanoid contraction.
Reason: The shielding effect of 4f electrons is relatively poor.
Consequences:
  • Decrease in basicity across the series.
  • Very small change in chemical properties making separation difficult.
  • Elements of the second (4d) and third (5d) transition series show similar atomic/ionic radii (e.g., Zr and Hf).

5. Coordination Chemistry

Give the difference between double salts and coordination compounds. Jun/2020, Aug/2021, Mar/2024
Sl.No Double Salt Coordination Compound
1 Completely dissociates into its constituent simple ions in solution. Never completely dissociates to give simple constituent ions in solution.
2 Loses its identity in solution. Does not lose its chemical identity in solution.
3 Example: Potash alum Example: K₄[Fe(CN)₆]
What are the limitations of Valence Bond (VB) theory? Aug/2021, Sept/2022
  • It does not explain the characteristic colour of complexes.
  • It considers only the spin-only magnetic moments and ignores other orbital components.
  • It does not provide a quantitative explanation for why certain ligands force inner orbital configurations while others form outer ones for the same metal.

6. Solid State

Define unit cell. Aug/2021, Sept/2022
The basic repeating structural unit of a crystalline solid that builds up the macroscopic crystal lattice is called a unit cell.
Differentiate between crystalline and amorphous solids. Jun/2020, May/2022, June/2023
Crystalline Solid Amorphous Solid
Definite characteristic geometric shape. Irregular or random shape.
Long-range orderly arrangement. Short-range order only.
Sharp melting points. Soften gradually over a range of temperature.
Anisotropic in nature. Isotropic in nature.
Explain Schottky and Frenkel defects. Sept/2020
Schottky Defect: Arises due to the missing of an equal number of cations and anions from the crystal lattice. It lowers the overall density of the crystal (e.g., NaCl).

Frenkel Defect: Arises when an ion is dislocated from its regular lattice point and occupies an intermediate interstitial position instead. It does not affect the density of the crystal (e.g., AgBr).

7. Chemical Kinetics

Differentiate between Rate and Rate Constant of a reaction. Aug/2021, June/2023
Rate of a Reaction Rate Constant
Represents the speed at which reactants are converted into products at any instant. It is a proportionality constant in the rate law expression.
Depends on the initial concentration of reactants. Independent of the initial concentration of reactants.
Derive the half-life period for a first-order reaction. June/2023
The integrated rate expression for a first-order reaction is:
K = (2.303 / t) * log([A₀] / [A])
When t = t₁/₂, the concentration [A] becomes [A₀]/2:
K = (2.303 / t₁/₂) * log([A₀] / ([A₀]/2))
t₁/₂ = (2.303 / K) * log(2)
t₁/₂ = 0.6932 / K

8. Ionic Equilibrium

Explain Common Ion effect with an example. Jun/2020, May/2022, Mar/2024
The suppression of the degree of dissociation of a weak electrolyte by the addition of a strong electrolyte containing a common ion is called the common ion effect.
Example: When sodium acetate (CH₃COONa) is added to a weak acetic acid (CH₃COOH) solution, the dissociation equilibrium of acetic acid shifts back, suppressing it due to the excess common acetate ion (CH₃COO⁻).
Derive the Henderson-Hasselbalch equation for an acid buffer. Mar/2020
Consider the dissociation of a weak acid HA:
Ka = [H₃O⁺][A⁻] / [HA]
Rearranging for [H₃O⁺]:
[H₃O⁺] = Ka * ([HA] / [A⁻])
Taking the negative logarithm on both sides:
-log[H₃O⁺] = -log(Ka) - log([HA] / [A⁻])
Since pH = -log[H₃O⁺], pKa = -log(Ka), [HA] = [Acid], and [A⁻] = [Salt]:
pH = pKa + log([Salt] / [Acid])

9. Electrochemistry

State Kohlrausch's law. Jun/2020
At infinite dilution, the limiting molar conductivity of an electrolyte is equal to the sum of the individual limiting molar conductances of its constituent anions and cations.
(Λ°_m)_NaCl = (λ°)_Na⁺ + (λ°)_Cl⁻
Derive Nernst equation. Sept/2020, May/2022, Sept/2022, Mar/2025
For a general redox reaction: xA + yB ⇔ lC + mD
The free energy change is given by: ΔG = ΔG° + RT ln Q
Substituting ΔG = -nFE_cell and ΔG° = -nFE°_cell:
-nFE_cell = -nFE°_cell + RT ln([C]^l [D]^m / [A]^x [B]^y)
Dividing both sides by -nF:
E_cell = E°_cell - (RT / nF) ln([C]^l [D]^m / [A]^x [B]^y)
Converting to log base 10 at 298 K:
E_cell = E°_cell - (0.0591 / n) log([C]^l [D]^m / [A]^x [B]^y)

10. Surface Chemistry

Differentiate between physisorption and chemisorption. Mar/2020, Mar/2024
Physical Adsorption (Physisorption) Chemical Adsorption (Chemisorption)
Caused by weak van der Waals forces. Caused by strong chemical bond formation.
Low heat of adsorption (~40 kJ/mol). High heat of adsorption (40-400 kJ/mol).
Reversible process, non-specific. Irreversible process, highly specific.
Forms multilayers on the adsorbent surface. Forms a uniform monolayer.
What is peptisation? Mar/2025
The dispersion of a freshly prepared precipitate into a stable colloidal sol by the addition of a small amount of a suitable electrolyte is termed peptisation. The electrolyte used is called the peptising agent.

11. Hydroxy Compounds and Ethers

How will you differentiate primary, secondary and tertiary alcohols by the Lucas test? Aug/2021, June/2023, Mar/2024
Alcohols are treated with Lucas reagent (a mixture of conc. HCl and anhydrous ZnCl₂) at room temperature:
  • Tertiary Alcohols: Give an immediate appearance of turbidity due to insoluble alkyl chloride.
  • Secondary Alcohols: Turbidity appears slowly within 5-10 minutes.
  • Primary Alcohols: Do not produce any turbidity at room temperature; turbidity appears only upon heating.
Write a note on Kolbe's reaction. Mar/2024
When phenol is treated with sodium hydroxide, sodium phenoxide is formed. It undergoes electrophilic aromatic substitution with carbon dioxide at 400K and 4-7 bar pressure to yield salicylic acid as the product:
C₆H₅ONa + CO₂ → C₆H₄(OH)COONa → C₆H₄(OH)COOH (Salicylic Acid)

12. Carbonyl Compounds

Write preparation of Urotropine and mention its uses. Jun/2020
Preparation: Formaldehyde reacts with ammonia to form hexamethylene tetramine (Urotropine):
6HCHO + 4NH₃ → (CH₂)₆N₄ + 6H₂O
Uses:
  • Used as a medicine to treat urinary tract infections.
  • Controlled nitration yields the explosive RDX.
Explain the mechanism of Aldol condensation. Mar/2024
  • Step 1: The base (OH⁻) abstracts an α-hydrogen from acetaldehyde to create a resonance-stabilised enolate ion.
  • Step 2: The nucleophilic enolate ion attacks the carbonyl carbon of another acetaldehyde molecule to form an alkoxide intermediate.
  • Step 3: The alkoxide abstracts a proton from water to yield 3-hydroxybutanal (Aldol), regenerating the catalyst.

13. Organic Nitrogen Compounds

Write a note on Gabriel Phthalimide Synthesis. Jun/2020, May/2022
This method is used exclusively for the preparation of pure aliphatic primary amines. Phthalimide is treated with alcoholic KOH to form potassium phthalimide, which is then reacted with an alkyl halide (R-X) to form N-alkyl phthalimide. Alkaline hydrolysis yields the primary amine:
Potassium Phthalimide + R-X → N-Alkyl Phthalimide → R-NH₂ (Primary Amine)
Why aniline does not undergo Friedel-Crafts reaction? Jun/2020, Apr/2023
Aniline is a strong Lewis base due to the lone pair on nitrogen. The catalyst AlCl₃ is a strong Lewis acid. They react together to form an unreactive coordinate complex adduct. This places a positive charge on the nitrogen atom, strongly deactivating the aromatic ring towards electrophilic attack.

14. Biomolecules

Give any three differences between DNA and RNA. Aug/2021
Feature DNA RNA
Sugar type Contains 2'-deoxyribose sugar. Contains ribose sugar.
Nitrogenous Bases Adenine, Thymine, Guanine, Cytosine. Adenine, Uracil, Guanine, Cytosine.
Structure Double-stranded helix. Single-stranded molecule.
What is a Zwitter ion? Give an example. Sept/2022, Apr/2023
In aqueous solution, the acidic carboxyl group of an amino acid can transfer its proton to the basic amino group of the same molecule. This results in a dipolar ion possessing equal positive and negative charges, making it electrically neutral.
Example: Glycine Zwitterion: ⁺H₃N-CH₂-COO⁻.

15. Chemistry in Everyday Life

How do antiseptics differ from disinfectants? Sept/2020
  • Antiseptics: Chemical substances that kill or prevent the growth of microorganisms; safe to be applied directly onto living tissues (e.g., Dettol, Povidone-Iodine).
  • Disinfectants: Stop or destroy microorganisms but are toxic to living cells; applied only to inanimate objects like floors or drainage systems (e.g., chlorine compounds).
Write a note on the vulcanization of rubber. Mar/2020, June/2023
Natural rubber is soft and sticky. Its physical properties are significantly enhanced by heating it with 3-5% elemental sulphur at 100-150°C. This sets up cross-linking disulphide bonds (-S-S-) between adjacent linear polyisoprene chains, making the rubber tougher, more elastic, and temperature resistant.