CHEMISTRY GLOSSARY

crystal system    →   kristalni sustav

Crystal system is a method of classifying crystalline substances on the basis of their unit cell. There are seven unique crystal systems. The simplest and most symmetric, the cubic (or isometric) system, has the symmetry of a cube. The other six systems, in order of decreasing symmetry, are hexagonal, tetragonal, rhombohedral (also known as trigonal), orthorhombic, monoclinic and triclinic.

Crystal system	Unit-cell	Conditions on unit-cell edges and angles
cubic		a=b=c α=β=γ=90°
hexagonal		a≠c α=γ=90° β=120°
tetragonal		a=b≠c α=β=γ=90°
rhombohedral		a=b=c α=β=γ≠90°
orthorhombic		a≠b≠c α=β=γ=90°
monoclinic		a≠b≠c α=γ=90°≠β
triclinic		a≠b≠c α≠β≠γ≠90°

diamond    →   dijamant

Diamond is the hardest known mineral (with a hardness of 10 on Mohs’ scale). It is an allotropic form of pure carbon that has crystallised in the cubic system, usually as octahedral or cubes, under great pressure. Diamond crystals my be colourless and transparent or yellow, brown or black. They are highly prized as gemstones, but also have extensive uses in industry, mainly for cutting and grinding tools. Diamonds occur in ancient volcanic pipes of kimberlite, or in river deposits that have been derived from weathered kimberlite. Industrial diamonds are being increasingly synthetically produced.

diatomaceous earth    →   dijatomejska zemlja

Diatomaceous earth is a naturally occurring siliceous sedimentary mineral compound from microscopic skeletal remains (frustules) of diatoms, unicellular aquatic plants of microscopic size. Their fossilized remains are called diatomite and contains approximately 3000 diatom frustules per cubic millimetre.

Diatomite is relatively inert and has a high absorptive capacity, large surface area, and low bulk density. It consists of approximately 90 % silica, and the remainder consists of compounds such as aluminum and iron oxides. The fine pores in the diatom frustules make diatomite an excellent filtering material for waters, beverages, oils, chemicals, as well as many other products.

electrophoresis    →   elektroforeza

Electrophoresis is a technique for the analysis and separation of colloids, based on the movement of charged colloidal particles in an electric field. The migration is toward electrodes of charge opposite to that of the particles. The rate of migration of the particles depends on the field, the charge on the particles, and on other factors, such as the size and shape of the particles.

Electrophoresis is important in the study of proteins. The acidity of the solution can be used to control the direction in which a protein moves upon electrophoresis.

enzyme    →   enzim

Enzyme is a protein that acts as a catalyst in biochemical reactions. Each enzyme is specific to a particular reaction or a group of similar reactions. Many require the association of certain nonprotein cofactors in order to function. The molecule undergoing a reaction (the substrate) binds to a specific active site on the enzyme molecule to form a short-lived intermediate: this greatly increases (by a factor of up to 10²⁰) the rate at which the reaction proceeds to form the product.

Geiger counter    →   Geigerov brojač

Geiger counter (Geiger-Muller counter) is a device used to detect and measure ionising radiation. It consists of a tube containing a low-pressure gas (usually argon or neon with methane) and a cylindrical hollow cathode through the centre of which runs a fine-wire anode. A potential difference of about 1 000 V is maintained between the electrodes. An ionising particle or photon passing through a window into the tube will cause an ion to be produced and the high potential will accelerate it towards its appropriate electrode, causing an avalanche of further ionisations by collision. The consequent current pulses can be counted in electronic circuits or simply amplified to work a small loudspeaker in the instrument. It was first devised in 1908 by the German physicist Hans Geiger (1882-1945). Geiger and W. Muller produced an improved design in 1928.

invert sugar    →   invertni šećer

Invert sugar is a mixture of equal parts of glucose and fructose resulting from the hydrolysis of sucrose (saccharose). The name stemming from the fact that it rotates of plane polarized light in the opposite direction of sucrose. Sucrose is dextrorotatory - it rotates polarized light clockwise ([α]_D = +66.5°). Invert sugar rotates the plane of the polarized light counterclockwise ([α]_D = -22°) due to the strongly levorotatory nature of fructose ([α]_D = -92°).

Homemade artificial honey (invert sugar syrup): Dissolve two parts of household sugar (1 kg) with stirring in one part of water (0.5 kg) in a saucepan over low heat. Add 1 g of citric acid or the juice of one lemon to the mixture. Bring the ingredients to a slow boil. It can take anywhere between 15 minutes to 1 hour. The end result is sticky, golden syrup. Let it sit at room temperature until it is cool.

Liebig condenser    →   Liebigovo hladilo

Liebig condenser is used for condensing of vapours that pass trough the centre tube. It is cooled with water that passes in the outer tube (shell around the centre tube) in the opposite direction than the one of hot vapour. Though named after the German chemist Justus von Liebig (1803-1873), he cannot be given credit for having invented it because it had already been in use for some time before him.

logarithmic scale    →   logaritamska skala

Logarithmic scale is the one in which values of 1, 2, 3, 4, 5, in fact represents values of 1, 10, 100, 1 000, 10 000. Logarithmic scales are often used to simplify graphs and tables, where otherwise changes of data at the lower end of the scale would be difficult to distinguish (e.g. a graph axis which would normally have values from 1 - 1 000 000 is shown by values of 1 - 7). An example of a logarithmic scale is the pH scale.

mass    →   masa

Mass (m) is the quantity of matter contained in a particle or body regardless of its location in the universe. Mass is constant, whereas weight is affected by the distance of a body from the centre of the Earth (or of other planet). The SI unit is kilogram.

According to the Einstein equation

all forms of energy possess a mass equivalent.