ICO Part B (ORI) key terms

A highly pure, stable reagent used to standardise a titrant solution by direct weighing, such as potassium hydrogen phthalate for base titration or potassium dichromate for redox work.

The procedure of determining the exact concentration of a working titrant solution by titrating it against a weighed amount of a primary standard or another solution of known concentration.

The point in a titration at which the amount of titrant added is stoichiometrically equivalent to the amount of analyte present, determined from the reaction equation rather than from colour change.

The observable change, usually a colour change of an indicator or an instrumental signal, that is taken as marking the completion of a titration and is ideally close to the equivalence point.

A method in which an excess of a standard reagent is added to the analyte and the unreacted remainder is then titrated, used when the direct reaction is slow or the end point is unclear.

A substance or instrument signal whose colour or response changes sharply near a particular pH, electrode potential, or reagent concentration, marking the end point of a titration.

The part of a titration or pH curve where added acid or base is largely consumed by a weak acid–conjugate base pair, so pH changes only slowly with volume added.

An expression relating the pH of a buffer to the acid dissociation constant and the ratio of conjugate base to acid concentrations, widely used to predict buffer pH and titration curve shape.

The equilibrium constant for loss of a proton from an acid in water, written Ka, with smaller values indicating weaker acids; its negative logarithm, pKa, is commonly tabulated.

The stoichiometric ratio of the molar mass of the sought substance to that of the weighed precipitate, multiplied by the mole ratio, converting precipitate mass into analyte mass.

Keeping a precipitate in contact with its mother liquor, often warm, so that small particles dissolve and reprecipitate onto larger ones, giving a purer, more filterable solid.

Contamination in which soluble impurities are carried down with a precipitate through adsorption, occlusion, or inclusion, causing a positive error in gravimetric analysis unless removed.

The relationship stating that absorbance of a dilute solution is proportional to the concentration of the absorbing species, the path length, and its molar absorption coefficient.

The proportionality constant in the Beer–Lambert law expressing absorbance per unit concentration per unit path length, characteristic of a species at a given wavelength and solvent.

The part of a molecule responsible for absorption of light in the ultraviolet or visible region, typically a conjugated system or a metal–ligand unit in a complex.

A plot of instrument response against known analyte concentrations, prepared with standards and used to convert sample response into concentration, ideally with regression statistics reported.

A quantitation method in which known amounts of analyte are added to portions of the sample itself, so that matrix effects are compensated in the extrapolated calibration.

Purification in which a solid is dissolved in a hot solvent or solvent mixture and allowed to crystallise on cooling, leaving most impurities in solution or in the discarded mother liquor.

The liquid remaining after crystals have formed and been filtered off, containing the soluble impurities and the portion of product that did not crystallise.

The ratio of the total concentrations of a solute in two immiscible phases at equilibrium, the key quantity governing extraction efficiency and solvent choice.

In chromatography, the distance travelled by a spot divided by the distance travelled by the solvent front, a dimensionless measure used to identify compounds by comparison with standards.

A measure of separation between two peaks, calculated from their retention times and peak widths, with larger values indicating better baseline separation of the components.

A separation mode in which components distribute between a stationary liquid phase and a moving mobile phase, so that differing distribution coefficients lead to different migration rates.

The amount of isolated product obtained, expressed as a mass or as a percentage of the theoretical maximum calculated from the limiting reagent and the balanced equation.

The reactant present in the smallest stoichiometric proportion, which is completely consumed first and therefore determines the maximum theoretical amount of product.

The fraction of the total mass of reactants that ends up in the desired product according to the balanced equation, used to judge the intrinsic efficiency of a synthetic route.

A manifold combining vacuum and inert-gas lines with stopcocks, allowing air- and moisture-sensitive compounds to be handled, filtered, and transferred under an inert atmosphere.

A sealed chamber with gloves and a purified inert atmosphere, used for storing and manipulating highly air- or moisture-sensitive materials and for weighing them free of oxygen.

Techniques such as syringe and cannula transfer, freeze–pump–thaw degassing, and use of septa that keep reagents and reactions free of oxygen and water during manipulation.

A ventilated enclosure with a moving sash that draws vapours and aerosols away from the operator, providing primary containment for toxic, corrosive, or flammable volatile materials.

A supplier document summarising a substance's hazards, including identification, first-aid measures, handling and storage advice, exposure limits, and disposal information required before use.

Engineering control that captures airborne contaminants at or near their source, such as a snorkel or hood, reducing operator exposure before contaminants enter the general room air.

An equation expressing reaction rate as a function of reactant concentrations and a rate constant, with the exponents giving the order with respect to each species.

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

The minimum energy that colliding molecules must possess for a reaction to proceed, obtained from the slope of an Arrhenius plot of the logarithm of the rate constant against reciprocal temperature.

The potential of a half-cell measured against the standard hydrogen electrode under standard conditions, quoted as a reduction potential and used to predict cell voltages and reaction spontaneity.

An equation relating the actual potential of an electrochemical cell to its standard potential and the reaction quotient, allowing prediction of cell voltage at non-standard concentrations.

A half-cell of stable, known potential, such as silver–silver chloride or calomel, against which the potential of an indicator or working electrode is measured in potentiometry.

The energy separation between d orbitals of a metal ion caused by the surrounding ligands, determining colour, magnetism, and high- or low-spin behaviour of a complex.

The net energy lowering of a transition-metal complex arising from preferential occupancy of lower-energy d orbitals in a given ligand field geometry, influencing structure and stability.

A measured response of a substance to an applied magnetic field, used to count unpaired electrons in a complex and so infer its spin state and oxidation state.

The greater thermodynamic stability of complexes with multidentate ligands compared with analogous complexes of monodentate ligands, largely due to favourable entropy of complexation.

The equilibrium constant for binding of a ligand to a metal ion to form a complex, often quoted stepwise or overall, and used to calculate speciation in solution.

The wavenumber at which a particular bond absorbs infrared radiation, diagnostic of functional groups and sensitive to coordination, hydrogen bonding, and oxidation state.

The position of an NMR signal relative to a reference, expressed in parts per million, reflecting the local electronic environment of the observed nucleus.

The spacing in hertz between split NMR signals arising from spin–spin interaction between neighbouring nuclei, giving information about connectivity and geometry.

The area under each NMR signal, proportional to the number of equivalent nuclei giving rise to it, used to establish relative numbers of protons or other observed nuclei.

The ion in a mass spectrum formed by loss of one electron from the intact molecule, whose mass gives the molecular mass and whose isotope pattern can reveal halogen content.

The characteristic cluster of mass spectral peaks separated by one mass unit arising from natural isotopic abundance, used to identify elements such as chlorine and bromine in a molecule.

The digits in a measured value that carry meaning about its precision, governing how many digits should be retained when results are combined by multiplication or addition.

The calculation of the combined uncertainty of a result from the uncertainties of the measured quantities, using relative uncertainties added in quadrature for multiplicative operations.

A statistical criterion, such as Dixon's or Grubbs' test, applied to decide whether a suspect measurement should be rejected rather than retained in the data set.

The straight line obtained by least-squares regression through calibration or kinetic data, whose slope and intercept are reported together with their uncertainties and correlation coefficient.