Tamil Nadu HSE Second Year Chemistry key terms

Heating a sulphide ore strongly in excess air so that the metal sulphide is converted to metal oxide, with sulphur escaping as sulphur dioxide gas.

Heating an ore strongly in limited air or in the absence of air to drive off water and carbon dioxide and to convert carbonates or hydrated oxides into oxides.

A concentration method in which powdered ore is agitated with water, oil and a frother so that sulphide particles become wetted by oil and rise with the foam while gangue settles.

The unwanted earthy or rocky impurity such as sand, clay or limestone mixed with an ore, which must be removed before the metal can be extracted economically.

A plot of the standard free energy of formation of metal oxides against temperature, used to predict whether a reducing agent can reduce a given metal oxide at a chosen temperature.

An ultrapurification technique in which a molten zone is moved slowly along a metal rod so that impurities dissolve in the melt and are carried to one end.

A purification method in which an impure metal is converted to a volatile iodide, which is then decomposed on a hot tungsten filament to deposit the pure metal.

An oxide that reacts with both acids and bases to form salts, such as aluminium oxide, which gives aluminium salts with acid and aluminates with alkali.

The tendency of the outermost s electrons in heavy p-block elements to remain unused in bonding, so that the element shows an oxidation state two less than its group maximum.

The ability of an element to link its own atoms into chains or rings; it is greatest for carbon and decreases sharply down the p-block groups.

The existence of an element in two or more different structural forms in the same physical state, such as diamond and graphite for carbon or rhombic and monoclinic sulphur.

An element whose atom or common ion has an incompletely filled d subshell, giving variable oxidation states, coloured ions, catalytic activity and paramagnetism.

The steady decrease in atomic and ionic radius across the lanthanoid series caused by poor shielding of the nuclear charge by the inner 4f electrons.

A non-stoichiometric compound formed when small atoms such as hydrogen, carbon or nitrogen occupy holes in a transition metal lattice, often making the metal harder and less ductile.

A measure of the strength of a magnet, for a transition metal ion calculated from the number of unpaired d electrons using the spin-only formula involving the square root of n(n+2).

An ion or molecule that donates one or more electron pairs to a central metal ion to form a coordinate bond in a complex.

The number of donor atoms directly attached to the central metal ion in a complex, commonly six for octahedral and four for tetrahedral or square planar complexes.

A complex in which a polydentate ligand grips the same metal ion through two or more donor atoms, forming a ring and usually giving extra stability.

The separation of the five d orbitals of a metal ion into groups of different energy when ligands approach, caused by electrostatic repulsion between ligand electrons and d electrons.

The smallest repeating portion of a crystal lattice which, when repeated in three dimensions, generates the whole crystal.

The percentage of the total volume of a unit cell that is actually occupied by the constituent particles; it is about 74 percent for close packing.

A point defect in ionic crystals in which a pair of oppositely charged ions is missing from the lattice, so the crystal stays electrically neutral but becomes less dense.

A point defect in which an ion leaves its normal lattice site and occupies an interstitial hole nearby, creating a vacancy and an interstitial ion without changing density.

A property whose value depends only on the present state of the system and not on the path taken to reach it, such as internal energy, enthalpy and entropy.

The enthalpy change when one mole of a compound is formed from its elements in their standard states at a specified temperature and pressure.

The statement that the overall enthalpy change of a reaction is the same whether it occurs in one step or several steps, because enthalpy is a state function.

A thermodynamic quantity combining enthalpy and entropy, whose decrease at constant temperature and pressure predicts that a process is spontaneous.

A measure of the disorder or randomness of a system; it increases when a solid melts, a liquid vaporises, or a gas expands into a larger volume.

The proportionality constant in a rate law that equals the rate of reaction when all reactant concentrations are unity; it depends on temperature and activation energy.

The sum of the powers of the concentration terms in the experimentally determined rate law; it may be zero, fractional or negative and is not fixed by the equation.

The time taken for the concentration of a reactant to fall to half its initial value; for a first-order reaction it is independent of the starting concentration.

The minimum extra energy that colliding reactant molecules must possess for a reaction to occur, related to the rate constant by the Arrhenius equation.

A solution that resists a marked change in pH when small amounts of acid or base are added, usually made from a weak acid with its salt or a weak base with its salt.

The amount of strong acid or base that a given volume of buffer can absorb with only a small change in pH; it is greatest when the acid and salt concentrations are equal.

The product of the molar concentrations of the ions of a sparingly soluble salt in a saturated solution, each raised to the power of its stoichiometric coefficient, at a given temperature.

The shift of an ionic equilibrium caused by adding an ion already present in the equilibrium mixture, which suppresses ionisation or lowers the solubility of a sparingly soluble salt.

The potential developed by a half-cell containing the electrode in contact with a solution of unit activity of its ions, measured against the standard hydrogen electrode at 298 K.

An equation relating the electrode potential or cell potential to the standard potential and the reaction quotient, allowing the effect of concentration and temperature to be calculated.

The maximum potential difference between the two electrodes of a galvanic cell when no current flows, equal to the difference of the two electrode potentials.

A cell in which an external source of electrical energy drives a non-spontaneous chemical reaction, with oxidation at the anode and reduction at the cathode.

The laws stating that the mass deposited or liberated at an electrode is proportional to the charge passed and to the equivalent mass of the substance.

The accumulation of molecules of a substance at the surface of a solid or liquid rather than throughout its bulk, driven by unbalanced surface forces.

Weak adsorption held by van der Waals forces; it is reversible, non-specific, forms multilayer films and is favoured by low temperature.

Strong adsorption in which the adsorbate forms chemical bonds with the surface; it is irreversible, specific, usually monolayer and favoured by high temperature.

The scattering of a beam of light by colloidal particles, which makes the path of the beam visible and helps distinguish a colloid from a true solution.

The conversion of a freshly prepared precipitate into a colloidal sol by adding a small amount of an electrolyte or by shaking with a suitable liquid.

A two-step nucleophilic substitution in which the halide first leaves to form a carbocation, which then combines with the nucleophile; racemisation and tertiary substrates favour it.

A one-step nucleophilic substitution in which the nucleophile attacks the carbon from the side opposite the leaving group, giving inversion of configuration and second-order kinetics.

When hydrogen halide adds to an unsymmetrical alkene, the hydrogen goes to the carbon bearing more hydrogens, so the halogen ends up on the more substituted carbon.

An equimolar mixture of the two enantiomers of a chiral compound, which is optically inactive because the rotations of the two forms cancel.

The conversion of a primary amide into a primary amine having one carbon less, brought about by bromine and alkali; the amine formed is purer than in other routes.

A test for primary amines in which the amine is warmed with chloroform and alcoholic potassium hydroxide to give an isocyanide with a foul smell.

An ion carrying both a positive and a negative charge on the same molecule, formed by an amino acid in neutral solution through internal acid-base reaction.

The pH at which an amino acid or protein carries no net charge and therefore does not migrate towards either electrode in an electric field.

The amide linkage formed between the carboxyl group of one amino acid and the amino group of another, with the loss of a water molecule.