الرئيسية » Simplified Chemistry (صفحه 21)

Simplified Chemistry

aldoximes

Compounds formed by reaction between hydroxylamine and an aldehyde RCOH + H2NOH → RCH:NOH + H2O  If R is an aliphatic group, the al­doxime is generally a liquid or low ­melting solid. If R is aromatic, the aldoxime is a crystalline solid. Al­doximes have a planar structure and can exist …

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affinity chromatography

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 …

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adsorption isotherm

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 …

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adiabatic demagnetization

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 …

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adiabatic approximation

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. …

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additive

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.

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Adams catalyst

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 …

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