CHSE Odisha Elective Chemistry flashcards

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

Bragg equation

For X-ray diffraction from crystal planes, nλ = 2d sinθ, where n is an integer order, λ the wavelength, d the interplanar spacing, and θ the glancing angle.

Body-centred cubic packing

A cubic unit cell with atoms at eight corners and one at the body centre; Z = 2 and packing efficiency is 68%, with atomic radius r = √3a/4.

Schottky defect

A stoichiometric point defect in ionic crystals in which equal numbers of cations and anions are missing from lattice sites, lowering density; favoured by small ions of similar size.

van't Hoff factor

The ratio i = observed colligative property / calculated property for the formula unit; it exceeds 1 for dissociation and is less than 1 for association in solution.

Nernst equation

E = E° − (RT/nF) ln Q, or at 298 K E = E° − (0.0591/n) log Q; it gives cell potential at non-standard concentrations and pressures.

Molar conductivity

Λm = κ × 1000 / M, where κ is conductivity in S cm⁻¹ and M is molar concentration; it increases on dilution because ion–ion interactions decrease.

Kohlrausch law

At infinite dilution, the molar conductivity of an electrolyte equals the sum of the limiting ionic conductivities of its ions, each multiplied by its stoichiometric coefficient.

First-order half-life

For a first-order reaction, t½ = 0.693/k; it is independent of initial concentration, so equal fractions react in equal time intervals.

Arrhenius equation

k = A e^(−Ea/RT), where A is the pre-exponential factor and Ea the activation energy; a plot of ln k versus 1/T has slope −Ea/R.

Pseudo-first-order reaction

A reaction whose rate depends on one reactant because all others are present in large excess, so their concentrations remain effectively constant; hydrolysis of an ester in excess water is an example.

Freundlich isotherm

Empirical adsorption relation x/m = k p^(1/n), where x/m is mass adsorbed per gram of adsorbent and p is pressure; 1/n lies between 0 and 1.

Hardy–Schulze rule

For coagulation of a negatively charged sol, the coagulating power of a cation increases with its charge; Al³⁺ is far more effective than Ba²⁺ or Na⁺.

Tyndall effect

Scattering of light by colloidal particles, making the beam path visible; it distinguishes a colloid from a true solution and depends on particle size and refractive index difference.

Roasting

Heating a sulphide ore strongly in excess air to convert it to an oxide and release sulphur dioxide; used for zinc blende and copper pyrites before reduction.

Ellingham diagram

A plot of standard Gibbs energy of formation of metal oxides versus temperature; the metal whose oxide curve lies lower can reduce the oxide of a metal above it.

Zone refining

Purification of silicon or germanium by passing a molten zone along a rod; impurities concentrate in the melt and are carried to the end, which is discarded.

Inert pair effect

The tendency of heavier p-block elements to show an oxidation state two units below the group maximum, because the ns² pair is poorly shielded and energetically stable.

Diborane bonding

B2H6 contains two three-centre two-electron B–H–B bridges plus four terminal B–H bonds; it is electron-deficient and dimerises aluminium chloride similarly through bridging.

Xenon tetrafluoride shape

XeF4 has four bond pairs and two lone pairs on xenon, giving square planar geometry with sp³d² hybridisation and a bond angle of 90°.

Crystal field splitting

The energy separation Δo between d orbitals in an octahedral complex; strong-field ligands give low-spin configurations and large splitting, weak-field ligands give high spin.

Lanthanoid contraction

The steady decrease in atomic and ionic radii from La to Lu caused by poor shielding of the increasing nuclear charge by 4f electrons; it affects properties of later transition metals.

Chelate effect

Enhanced stability of a complex formed by polydentate ligands that bind through several donor atoms, because ring formation gives a favourable entropy change on ligand substitution.

Linkage isomerism

Isomerism shown by ambidentate ligands such as NO2⁻ or SCN⁻, which can bond through either of two different donor atoms, giving nitrito and nitro or thiocyanato and isothiocyanato forms.

SN1 mechanism

A two-step nucleophilic substitution with a carbocation intermediate; rate depends only on the substrate, and tertiary halides in polar protic solvents react fastest.

Lucas test

Concentrated HCl with anhydrous ZnCl2 distinguishes alcohols: tertiary turns cloudy immediately, secondary on warming, and primary only on heating or not at all.

Williamson synthesis

Formation of an ether by nucleophilic attack of an alkoxide ion on a primary alkyl halide; secondary and tertiary halides favour elimination instead.

Tollens' test

Ammoniacal silver nitrate gives a silver mirror with aldehydes but not ketones; the aldehyde is oxidised to carboxylate while Ag⁺ is reduced to Ag.

Cannizzaro reaction

Disproportionation of an aldehyde lacking α-hydrogen, such as benzaldehyde, in concentrated alkali, giving equal amounts of alcohol and carboxylate salt.

Hinsberg test

Reaction of amines with benzenesulphonyl chloride: primary amines give a soluble sulphonamide after alkali, secondary give an insoluble one, tertiary do not react.

Peptide bond

An amide linkage formed between the carboxyl group of one amino acid and the amino group of another with loss of water; it is planar and partly double-bonded.

Addition polymerisation

Monomer molecules containing carbon–carbon double bonds join without loss of any small molecule; polyethylene and polyvinyl chloride form this way.

Vulcanisation

Heating natural rubber with sulphur to create cross-links between cis-1,4-polyisoprene chains, increasing strength, elasticity and resistance to temperature change.