BSEB Intermediate Chemistry key terms

The number of gram-equivalents of solute dissolved in one litre of solution. It equals molarity multiplied by the n-factor of the solute, and is used in acid-base and redox titrations.

The number of moles of solute present in one litre of solution. It changes with temperature because solution volume expands or contracts, unlike molality which uses solvent mass.

The number of moles of solute dissolved in one kilogram of solvent. Because it uses mass, not volume, molality is independent of temperature and is preferred for colligative property calculations.

Properties that depend only on the number of solute particles, not their identity: relative lowering of vapour pressure, boiling point elevation, freezing point depression, and osmotic pressure.

The ratio of observed colligative effect to the value expected for a non-dissociating solute. It exceeds one for electrolytes that dissociate and falls below one for solutes that associate.

The excess pressure that must be applied to a solution to stop solvent from flowing into it through a semipermeable membrane. It equals CRT for dilute solutions.

For a solution of volatile liquids, the partial vapour pressure of each component equals its mole fraction in the liquid multiplied by the vapour pressure of the pure component.

A liquid mixture that boils at constant temperature and distils without change in composition because vapour and liquid have the same composition. Ethanol-water forms a minimum-boiling azeotrope.

The potential of a half-cell measured against the standard hydrogen electrode under standard conditions: 1 M concentration, 1 bar gas pressure, and 298 K.

An equation giving electrode potential at non-standard concentrations: E equals E° minus (RT/nF) ln Q. At 298 K it is often written with 0.0591/n.

The difference between the reduction potentials of the cathode and anode half-cells when no current flows. A positive EMF means the cell reaction is spontaneous.

A list of half-reactions arranged by standard reduction potential. Species higher in the list are stronger oxidising agents and are reduced preferentially.

The mass deposited or liberated at an electrode is proportional to charge passed, and for a given charge, masses of different substances are proportional to their equivalent masses.

The reciprocal of resistivity, measuring how well a solution carries current. It decreases on dilution for strong electrolytes because ion concentration falls.

Conductivity divided by molar concentration, expressed in S cm² mol⁻¹. It increases on dilution and reaches a limiting value for strong electrolytes.

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

An experimentally determined expression relating reaction rate to concentrations of reactants, each raised to a power called its order. It cannot generally be written from stoichiometry alone.

The sum of the powers of concentration terms appearing in the experimentally determined rate law. It may be zero, fractional, or negative.

The number of reacting species colliding simultaneously in an elementary step. It is always a small whole number and has no meaning for an overall complex reaction.

The proportionality constant k in the rate law, equal to the rate when all reactant concentrations are unity. Its units depend on the overall order.

The time taken for reactant concentration to fall to half its initial value. For a first-order reaction it is independent of initial concentration and equals 0.693/k.

The minimum extra energy reactant molecules must possess to form products. It equals the difference between threshold energy and average energy of reactants.

An equation relating rate constant to temperature: k equals A e^(−Ea/RT), where A is the frequency factor and Ea the activation energy.

Elements with partially filled d orbitals in the atom or in a common oxidation state. They show variable oxidation states, coloured ions, and catalytic activity.

The steady decrease in atomic and ionic radii across the lanthanoids due to poor shielding of nuclear charge by 4f electrons. It causes similarity between Zr and Hf.

Compounds formed when small atoms such as hydrogen, carbon, or nitrogen occupy holes in a metal lattice. They are hard, retain metallic conductivity, and often have high melting points.

An ion or molecule that donates one or more electron pairs to a central metal ion to form a coordinate bond in a complex. Examples include NH₃, Cl⁻, and EDTA.

The number of donor atoms directly bonded to the central metal ion in a complex. It is commonly 4 or 6, giving tetrahedral or octahedral geometry.

A complex in which a polydentate ligand binds the metal through two or more donor atoms, forming a ring. Chelates are usually more stable than comparable unidentate complexes.

A model explaining colour and magnetism of complexes by the splitting of metal d orbitals into different energy levels under the electrostatic field of ligands.

A nucleophilic substitution proceeding in two steps through a carbocation intermediate. Rate depends only on substrate concentration, and racemisation with inversion is common.

A one-step nucleophilic substitution in which the nucleophile attacks as the leaving group departs. Rate depends on both substrate and nucleophile, and the product is inverted.

Preparation of an ether by treating an alkoxide with a primary alkyl halide through SN2 attack. Primary halides give good yields; tertiary halides favour elimination.

Formylation of phenol with chloroform and aqueous sodium hydroxide, giving salicylaldehyde as the major product after acid work-up.

Treatment of sodium phenoxide with carbon dioxide under pressure followed by acidification, giving salicylic acid, with the carboxyl group entering mainly at the ortho position.

Disproportionation of aldehydes lacking alpha-hydrogens, such as benzaldehyde, in concentrated alkali, giving one molecule of alcohol and one of carboxylate salt.

Base-catalysed reaction of two carbonyl compounds having alpha-hydrogens to form a beta-hydroxy carbonyl, which dehydrates on heating to an alpha,beta-unsaturated carbonyl.

Conversion of a primary amide to a primary amine with one fewer carbon atom by heating with bromine and alkali. The amine formed is smaller by one carbon.

A test in which a primary amine is warmed with chloroform and alcoholic potassium hydroxide to give an isocyanide with a foul smell. Secondary and tertiary amines do not respond.

Cyclic stereoisomers of a sugar differing only in the configuration at the anomeric carbon, giving alpha and beta forms that interconvert in solution through mutarotation.

The amide linkage formed between the carboxyl group of one amino acid and the amino group of another, with loss of water. It joins amino acids in proteins.

The tendency of heavier p-block elements to show an oxidation state two less than the group maximum, because the ns² pair is reluctant to take part in bonding.

The existence of an element in two or more structural forms in the same physical state, such as diamond and graphite for carbon, or white and red phosphorus.

A qualitative test in which a clean nichrome wire dipped in a salt is heated in a flame. Characteristic colours identify certain metal ions, such as sodium and potassium.

A test for nitrate ions in which the salt is heated with iron(II) sulphate and concentrated sulphuric acid is added slowly, giving a brown ring of a nitrosyl complex.