CHEMISTRY GLOSSARY

anode    →   anoda

Anode is the electrode at which oxidation occurs in a cell. Anions migrate to the anode.

Anode is a positive electrode on which reaction of oxidation is developed (loss of electrons).

aqueous solution    →   vodena otopina

Aqueous solutions are those solutions where water is the solvent. An aqueous solution found in an equation describing a chemical reaction is denoted by the state symbol, (aq).

acid    →   kiselina

Acid is a type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction for an acid HA is commonly written:

In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is:

This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and produce colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water, (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. acetic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant.

In the Lowry-Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). An important feature of the Lowry-Brønsted concept is that when an acid gives up a proton, a conjugate base is formed that is capable of accepting a proton.

Similarly, every base produces its conjugate acid as a result of accepting a proton.

For example, acetate ion is the conjugate base of acetic acid, and ammonium ion is the conjugate acid of ammonia.

As the acid of a conjugate acid/base pair becomes weaker, its conjugate base becomes stronger and vice versa.

A further extension of the idea of acids and bases was made in the Lewis theory. In this, a G. N. Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses "traditional" acid-base reactions, but it also includes reactions that do not involve ions, e.g.

in which NH₃ is the base (donor) and BCl₃ the acid (acceptor).

azo compounds    →   azo-spojevi

Azo compounds are organic compounds containing the group -N=N- linking two other groups. They can be formed by reaction of a diazonium ion with a benzene ring.

Boudouard’s equilibrium    →   Boudouardova ravnoteža

Boudouard’s equilibrium is established when carbon dioxide reacts with carbon. Because of reactions endothermity the temperature increase shifts the reaction rightwards and the temperature reduction leftwards.

Bronsted acid    →   Bronstedova kiselina

Brøsted acid is a material that gives up hydrogen ions in a chemical reaction.

Bronsted base    →   Bronstedova baza

Brønsted base is a material that accepts hydrogen ions in a chemical reaction.

active site    →   aktivno mjesto

Active site is a pocket or crevice on an enzyme molecule that fits reactant molecules like a hand in a glove. The active site lowers the activation energy for reaction

alkaline earth metal    →   zemnoalkalijski metal

Alkali earth metal is a term that refers to six elements: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These elements make up group 2 of the periodic table of elements. They all exhibit a single oxidation state, +2. They are all light and very reactive. Barium and radium are the most reactive and beryllium is the least.

To denote slightly soluble metal oxides chemists formerly used the term "earth". The oxides of barium, strontium, and calcium resemble alumina (Al₂O₃), a typical "earth", but form alkaline mixtures with water. For this reason barium, strontium, and calcium were called alkaline earth metals. This name has now been extended to include all of the elements of group 2.

alkanes    →   alkani

Alkanes (paraffins) are acyclic branched or unbranched hydrocarbons having the general formula C_nH_2n+2, and therefore consisting entirely of hydrogen atoms and saturated carbon atoms. In the systematic chemical nomenclature alkane names end in the suffix -ane. They form a homologous series (the alkane series) methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), etc. The lower members of the series are gases; the high-molecular mass alkanes are waxy solid. Generaly the alkanes are fairly unreactive. They form haloalkanes with halogens when irradiated with ultraviolet radiation. Alkanes are present in natural gas and petroleum.