back titration : A technique in volumetric analysis in which a known excess amount of a reagent is added to the solution to be estimated. The unreacted amount of the added reagent is then determined by titration, allowing the amount of substance in the original test solution to be calculated. بوسترات (لوحات) كيميائية بدقة عالية (أكثر من 25 لوحة) …
أكمل القراءة »Simplified Chemistry
background radiation
Low intensity ionizing radiation present on the surface of the earth and in the atmosphere as a result of cosmic radiation and the presence of radioisotopes in the earth’s rocks, soil, and atmosphere. The radioisotopes are either natural or the result of nuclear fallout or waste gas from power stations. Background counts must be taken into account when measuring the …
أكمل القراءة »backbiting
A rearrangement that can occur in some polymerization reactions involving free radicals. A radical that has an unpaired electron at the end of the chain changes into a radical with the unpaired electron elsewhere along the chain, the new radical being more stable than the one from which it originates. For example, the radical RCH2CH2CH2CH2CH2CH2· may change into RCH2CH·CH2CH2CH2CH3 The rearrangement …
أكمل القراءة »Babbit metal
Any of a group of related alloys used for making bearings. They consist of tin containing antimony (about 10%) and copper (1-2%), and often lead. The original alloy was invented in 1839 by the US inventor Isaac Babbit (1799-1862).
أكمل القراءة »allosteric enzyme
An enzyme that has two structurally distinct forms, one of which is active and the other inactive. In the active form, the quaternary structure of the enzyme is such that a substrate can interact with the enzyme at the active site. The conformation of the substrate-binding site becomes altered in the inactive form and interaction with the substrate is not …
أكمل القراءة »allenes
Compounds that contain the group >C=C=C<, in which three carbon atoms are linked by two adjacent double bonds. The outer carbon atoms are each linked to two other atoms or groups by single bonds. The simplest example is 1,2-propadiene, CH2CCH2 . Allenes are dienes with typical reactions of alkenes. Under basic conditions. they often convert to alkynes. In an allene, …
أكمل القراءة »alkyd resin
A type of polyester resin used in paints and other surface coating. The original alkyd resins were made by copolymerizing phthalic anhydride with glycerol, to give a brittle cross-linked polymer. The properties of such resins can be modified by adding monobasic acids or alcohols during the polymerization.
أكمل القراءة »(algin (alginic acid
A complex polysaccharide occurring in the cell walls of the brown algae (Phaeophyta). Algin strongly absorbs water to form a viscous gel. It is produced commercially from a variety of species of Laminaria and from Macrocystis pyrifera in the form of alginates, which are used mainly as a stabilizer and texturing agent in the food industry.
أكمل القراءة »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 in two isomeric forms. In the syn-form, the OH group …
أكمل القراءة »aldosterone
A hormone produced by the adrenal glands that controls excretion of sodium by the kidneys and thereby maintains the balance of salt and water in the body fluids.
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