Simplified Chemistry

affinity chromatography A bio­chemical technique for purifying nat­ural polymers, especially proteins. It functions by attaching a specific lig­and by covalent bonding to an insolu­ble inert support. The ligand has to have a specific affinity for the poly­mer, so that when a solution contain­ing the ligand is passed down a column of the material it is specifi­cally retarded and thus separated …

A low-density porous trans­parent material that consists of more than 90% air. Usually based on metal oxides or silica, aerogels are used as drying agents and insulators.

adsorption isotherm An equation that describes how the amount of a substance adsorbed onto a surface de­pends on its pressure (if a gas) or its concentration (if in a solution), at a constant temperature. Several ad­sorption isotherms are used in sur­face chemistry including the BET isotherm and the Langmuir ad­sorption isotherm. The different isotherms correspond to different as­sumptions about the …

adsorption indicator (absorption indicator) A type of indicator used in reactions that involve precipita­tion. The yellow dye fluorescein is a common example, used for the reac­tion NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq) As silver nitrate solution is added to the sodium chloride, silver chlo­ride precipitates. As long as Cl” ions are in excess, they adsorb on the precipitate particles. …

A technique for cooling a paramagnetic salt, such as potassium chrome alum, to a temperature near absolute zero. The salt is placed between the poles of an electromagnet and the heat produced during magnetization is re­moved by liquid helium. The salt is then isolated thermally from the sur­roundings and the field is switched off; the salt is demagnetized adiabati­cally and …

adiabatic approximation An ap­proximation used in quantum me­chanics when the time dependence of parameters, such as the internuclear distance between atoms in a molecule, is slowly varying. This ap­proximation means that the solution of the Schrodinger equation at one time goes continuously over to the solution at a later time. It was formu­lated by Max Born and the Soviet physicist …

A substance added to another substance or material to improve its properties in some way. Additives are often present in small amounts and are used for a variety of purposes, as in preventing corrosion, stabilizing polymers, and preserving and improving foods.

A dark brown powder, a hydrated form of platinum (IV) oxide (PtO2), produced by heating chloroplatinic acid (H2PtC16) with sodium nitrate (NaNO3). Platinum ni­trate is produced, and this decom­poses to Platinum (IV) oxide with evolution of NO2 and oxygen. It is used in hydrogenations of alkenes to alkanes, nitro compounds to aminos, and ketones to alcohols. The actual catalyst is …

A colourless crys­talline hydrocarbon C10H16; m.p. 269°C. It is found in certain petro­leum fractions. The structure con­tains three symmetrically fused cyclohexane rings.

The process of introducing an acyl group (RCO-) into a compound. The usual method is to react an alcohol with an acyl halide or a carboxylic acid anhydride; e.g. RCOCl + R’OH → RCOOR’ + HCl