Tamil Nadu HSE Second Year Chemistry flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Froth flotation

Concentration method for sulphide ores in which oil froth wets the ore particles selectively, floating them to the surface while gangue settles; used for ZnS and PbS.

Ellingham diagram

Plot of standard free energy of formation of metal oxides against temperature. The lowest curve is the most stable oxide; a metal can reduce oxides of metals whose curves lie above it.

Calcination versus roasting

Calcination heats an ore in limited or no air (carbonates to oxides); roasting heats it in excess air (sulphides to oxides). Both drive off volatile impurities.

Cryolite in aluminium extraction

Na3AlF6 dissolves alumina in the Hall–Héroult cell, lowering the melting point from about 2045 °C to near 950 °C and improving conductivity of the electrolyte.

Mond process

Refining of nickel: impure Ni reacts with CO near 50–60 °C to give volatile Ni(CO)4, which decomposes near 180 °C to deposit pure nickel.

Nitrogen inertness

The N≡N triple bond has very high bond enthalpy (941 kJ/mol), making nitrogen gas unusually unreactive at room temperature despite being a small diatomic molecule.

Ozone structure

O3 is a bent molecule with bond angle about 116.8°, diamagnetic, and a powerful oxidiser that liberates iodine from acidified potassium iodide solution.

Interhalogen compounds

Compounds formed between two different halogens, such as ClF3, BrF5, and IF7, in which the larger, less electronegative halogen is the central atom.

Xenon tetrafluoride geometry

XeF4 has a square planar shape, consistent with sp3d2 hybridisation and two lone pairs occupying axial positions to minimise repulsion.

Transition element definition

An element with an incompletely filled d subshell in its atom or in a common oxidation state; zinc, cadmium, and mercury are therefore excluded.

Lanthanoid contraction

The steady decrease in ionic radius from lanthanum to lutetium caused by poor shielding of the nucleus by 4f electrons, making later lanthanoids smaller than expected.

Spin-only magnetic moment

μ = √(n(n+2)) Bohr magnetons, where n is the number of unpaired electrons; used to distinguish high-spin and low-spin complexes.

Interstitial compounds

Compounds formed when small atoms such as carbon or nitrogen occupy holes in a transition metal lattice; they are hard, high melting, and retain metallic conductivity.

EDTA ligand denticity

EDTA4− is hexadentate: it binds a metal ion through two nitrogen atoms and four carboxylate oxygen atoms, forming a very stable chelate ring system.

Spectrochemical series

Order of ligand field strength: I− < Br− < Cl− < F− < OH− < H2O < NH3 < en < NO2− < CN− < CO; stronger ligands cause larger splitting.

Effective atomic number rule

EAN = atomic number − oxidation state + 2 × coordination number; complexes are stable when EAN equals the next noble gas configuration.

Crystal field splitting

In an octahedral field d orbitals split into lower t2g and higher eg sets with gap Δo; tetrahedral splitting is about four-ninths of Δo.

Schottky defect

A pair of missing cation and anion sites in an ionic crystal; density decreases and the defect is favoured by high coordination number and similar ion sizes.

F-centre

An anion vacancy occupied by a trapped electron in a metal-excess defect; it absorbs visible light and gives crystals such as NaCl a yellow colour.

Bragg equation

nλ = 2d sinθ, relating X-ray wavelength, angle of diffraction, and interplanar spacing; used to determine crystal lattice parameters.

Radius ratio rule

The ratio of cation to anion radius predicts coordination number: 0.225–0.414 tetrahedral, 0.414–0.732 octahedral, and 0.732–1.0 cubic.

Gibbs free energy criterion

ΔG = ΔH − TΔS; a reaction is spontaneous when ΔG is negative, at equilibrium when ΔG = 0, and non-spontaneous when positive.

Hess's law

The enthalpy change of a reaction is independent of the route taken; it allows ΔH to be calculated from standard enthalpies of formation of reactants and products.

First-order half-life

For a first-order reaction t1/2 = 0.693/k, independent of initial concentration; this constancy is a diagnostic test for first-order kinetics.

Arrhenius equation

k = A e^(−Ea/RT); a plot of ln k against 1/T is linear with slope −Ea/R and intercept ln A, allowing activation energy determination.

Henderson–Hasselbalch equation

pH = pKa + log([salt]/[acid]) for an acidic buffer; buffer capacity is greatest when the salt and acid concentrations are equal, that is pH = pKa.

Solubility product

Ksp is the product of ion concentrations in a saturated solution, each raised to its stoichiometric coefficient; precipitation occurs when the ionic product exceeds Ksp.

Nernst equation

E = E° − (0.0591/n) log Q at 25 °C; it relates cell potential to reaction quotient and gives E = 0 for a concentration cell with identical electrodes.

Kohlrausch's law

The limiting molar conductivity of an electrolyte equals the sum of the limiting molar conductivities of its individual ions, useful for weak electrolytes.

Hardy–Schulze rule

The coagulating power of an ion on a colloidal sol increases with the magnitude of its charge; Al3+ coagulates a negative sol far better than Ca2+ or Na+.

SN1 versus SN2

SN1 is two-step via carbocation, first order, favoured by tertiary halides; SN2 is one-step, second order, favoured by primary halides and gives inversion.

Hofmann bromamide degradation

A primary amide treated with bromine and alkali gives a primary amine containing one carbon fewer, with the carbonyl carbon lost as carbonate.