Simplified Chemistry

A type of presump­tive test in which a substance is identified by the formation of charac­teristic crystals when a certain reagent is added. Usually, such tests are conducted using a microscope (microcrystal test). An example is the acetone-chlor-haemin test for blood.

A resin obtained from the bark of South American trees of the genera Strychnos and Chondrodendron that causes paralysis of voluntary muscle. It acts by blocking the action of the neurotransmitter  acetyl­choline at neuromuscular junctions. Curare is used as an arrow poison by South American Indians and was for­merly used as a muscle relaxant in surgery.

The susceptibility (X) of a paramagnetic substance is propor­tional to the thermodynamic temper­ature (T), i.e. x = C/T, where C is the Curie constant. A modification of this law, the Curie-Weiss law, is more generally applicable. It states that  X = C/(T- θ), where θ is the Weiss constant, a characteristic of the ma­terial. The law was first proposed by …

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.

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.

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 …

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 …

 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[exp(1 – a)Fη/RT- exp(- aF/RT)] where ja and jc are the individual cathode and anode currents espect­tively, and je is the equilibrium cur­rent, called the exchange …

 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 …

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 …