Simplified Chemistry

 

cycloaddition

A reaction in which two or more unsaturated compounds form a cyclic adduct or in which a cyclic compound is formed by addi­tion between unsaturated parts of the same molecule. In cycloaddition, there is no net reduction in bond multiplicity. The Diels-Alder reac­tion is an example. Cycloadditions may be stepwise reactions or may be peri-cyclic reactions.

كلمات دليلية: , ,

cyclophane

A compound consist­ing of one or more aromatic rings forming part of a larger ring system in which aliphatic chains of the CH2 groups link the aromatic rings. Com­pounds of this type have the suffix phane in their names. Depending on the sizes of the (CH2)11 chains, the aro­matic rings may not be planar.

كلمات دليلية: ,

LABORATORY REAGENTS FOR GENERAL USE

 

DILUTE ACIDS

3 molar. Use the amount of concentrated acid indicated and dilute to one liter. Acetic acid, 3 N. Use 172 ml of 17.4 M acid (99-100%). Hydrochloric acid, 3 N. Use 258 ml of 11.6 M acid (36% HCI). Nitric acid, 3 N. Use l95 ml of 15.4 M acid (69% HNO3). Phosphoric acid, 9 N. Use 205 ml of 14.6 M acid (85% H3PO4) Sulfuric acid, 6…

كلمات دليلية: ,

Brownian movement

Brownian movement The contin­uous random movement of micro­scopic solid particles (of about 1 micrometre in diameter) when sus­pended in a fluid medium. First observed by the British botanist Robert Brown (1773-1858) in 1827 when studying pollen particles, it was origi­nally thought to be the manifestation of some vital force. It was later recog­nized to be a consequence of bom­bardment of the particles by the continually moving…

كلمات دليلية: , ,

buffer

A solution that resists change in pH when small amounts of an acid or alkali are added over a cer­tain range or when the solution is di­luted. Acidic buffers consist of a weak acid with a salt of the acid. The salt provides the negative ion A-, which is the conjugate base of the acid HA. An example is carbonic acid and sodium hydrogencarbonate. Basic buffers have a…

كلمات دليلية: ,

buna rubber

A type of synthetic rubber based in polymerization of butadiene (buta-1,3-diene). The name comes from Bu (for butadiene) and Na (for sodium, which was used as a catalyst in the original polymeriza­tion reaction). An improved form, known as Buna-S was developed by copolymerizing butadiene with styrene. In 1934, Buna-N was in­vented, in which the styrene was re­placed by acrylonitrile, giving a product with better oil resistance.

كلمات دليلية: , , , , ,

Butler-Volmer equation

 An equation for the rate of an electro­chemical reaction; it describes the current density at an electrode in terms of the overpotential. The But­ler-Volmer equation is given by:

j = ja – jc = je

where ja and jc are the individual cathode and anode currents espect­tively, and je is the equilibrium cur­rent, called the exchange current density. By definition

je =…

كلمات دليلية: , , , , ,

(B-Z reaction (Belousov-Zhabotin­skii reaction

 A chemical reaction that shows a periodic colour change between magenta and blue with a pe­riod of about one minute. It occurs with a mixture of sulphuric acid, potassium bromate(V), cerium sul­phate, and propanedioic acid. The colour change is caused by alternat­ing oxidation-reductions in which cerium changes its oxidation state (Ce3+ gives a magenta solution while Ce4+ gives a blue solution). The B-Z reaction is an example of…

كلمات دليلية: , ,

anabolic steroids

Steroid hor­mones related to the male sex hor­mone testosterone. They promote the development of masculine char­acteristics and increase muscle growth. Anabolic steroids have been used medically for various conditions but are also used illegally by sports­men and women and by body­builders. They have a number of deleterious side effects and are a con­trolled drug in the UK and many other countries. Their use is banned by nearly all…

كلمات دليلية: , , , , ,

amperometric titration

A method of determining the chemical composition of a solution by measur­ing the current passing through a cell containing the solution; the po­tential is held constant during the titration for both the indicator and reference electrodes, with changes in the current being measured. The cur­rent flowing through the cell is meas­ured as a function of the amount of substance being titrated.

كلمات دليلية: , ,