Simplified Chemistry

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) …

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 …

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 …

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).

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 …

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, …

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.

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.

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 …

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.