CHEMISTRY GLOSSARY

volt    →   volt

Volt (V) is the SI derived unit of electric potential. One volt is the difference of potential between two points of an electric conductor when a current of 1 ampere flowing between those points dissipates a power of 1 watt. It was named after the Italian physicist Alessandro Volta (1745-1827).

galvanic celll    →   galvanski članak

Galvanic cell (voltaic cell) is a simple device with which chemical energy is converted into electrical energy. Galvanic cells consist of two separate compartments called half cells containing electrolyte solutions and electrodes that can be connected in a circuit. Two dissimilar metals (e.g., copper and zinc) are immersed in an electrolyte. If the metals are connected by an external circuit, one metal is reduced (i.e., gains electrons) while the other metal is oxidized (i.e., loses electrons).

In the example above, copper is reduced and zinc is oxidized. The difference in the oxidation potentials of the two metals provides the electric power of the cell.

A voltaic cell can be diagrammed using some simple symbols. In the diagram the electrodes are on the outer side of the diagram and a vertical line (|) is used to separate the electrode from the electrolyte solution found in the compartment. A double vertical line (||) is used to separate the cell compartments and is symbolic of the salt bridge. Usually in a diagram the species oxidized is written to the left of the double slash. Here is an example of the Daniell cell:

The names refer to the 18th-century Italian scientists Alessandro Volta (1745-1827) and Luigi Galvani (1737-1798).

halocarbon    →   halogenirani ugljikovodik

Halocarbon is a compound containing no elements other than carbon, one or more halogens, and sometimes hydrogen. The simplest are compounds such as tetrachloromethane (CCl₄), tetrabromomethane (CBr₄), etc. The lower members of the various homologous series are used as refrigerants, propellant gases, fireextinguishing agents, and blowing agents for urethane foams. When polymerized, they yield plastics characterized by extreme chemical resistance, high electrical resistivity, and good heat resistance.

weak electrolyte    →   slabi elektrolit

Weak electrolytes are those electrolytes which in water solutions dissociate only partially, giving ions and which are in equilibrium with undissociated molecules. Their water solutions conduct electric current weakly. For example, acetic acid partially dissociates into acetate ions and hydrogen ions, so that an acetic acid solution contains both molecules and ions.

weber    →   veber

Weber (Wb) is the SI derived unit of magnetic flux. The weber is the magnetic flux which, linking a circuit of one turn, produces in it an electromotive force of one volt as it is reduced to zero at a uniform rate in one second (Wb = V·s). The unit was named after the German scientist W.E. Weber (1804-1891).

Zeeman, Pieter    →   Zeeman, Pieter

Pieter Zeeman (1865-1943) was a Dutch physicist who discovered the splitting of the spectral lines of a substance when placed in a magnetic field (known as the Zeeman effect). In 1902, Zeeman and Lorentz were jointly awarded the Nobel Prize in Physics, for their, extraordinary service they rendered by their researches into the influence of magnetism upon radiation phenomenon.

glass electrode    →   staklena elektroda

Glass electrode is a hydrogen-ion responsive electrode usually consisting of a bulb, or other suitable form, of special glass attached to a stem of high resistance glass complete with internal reference electrode and internal filling solution system. Glass electrode is also available for the measurement of sodium ions.

The glass electrode, which consists of a thin wall glass bulb, has an extremely high electrical resistance. The membrane of a typical glass electrode (with a thickness of 0.03 mm to 0.1 mm) has an electrical resistance of 30 MΩ to 600 MΩ. The surface of a glass membrane must be hydrated before it will function as a pH electrode. When a glass surface is immersed in an aqueous solution then a thin solvated layer (gel layer) is formed on the glass surface in which the glass structure is softer. This applies to both the outside and inside of the glass membrane.

The simplest explanation for the working of the thin glass electrode is that the glass acts as a weak acid (Glass-H).

The hydrogen ion activity of the internal solution is held constant. When a solution of different pH from the inside comes in contact with the outside of the glass membrane, the glass is either deprotonated or protonated relative to the inside of the glass. The difference in pH between solutions inside and outside the thin glass membrane creates electromotive force in proportion to this difference in pH.

krypton    →   kripton

Krypton was discovered by Sir William Ramsay and Morris W. Travers (England) in 1898. The origin of the name comes from the Greek word kryptos meaning hidden. It is colourless, odourless rare noble gas. Reacts only with fluorine. Krypton is obtained from production of liquid air. Used in lighting products. Some is used as inert filler-gas in incandescent bulbs. Some is mixed with argon in fluorescent lamps. The most important use is in flashing stroboscopic lamps that outline airport runways.

luminescence    →   luminiscencija

Luminescence (from Latin lumen, light) is the emission of electromagnetic radiation (UV, visible or IR) from atoms or molecules as a result of the transition of an electronically excited state to a lower energy state, usually the ground state. Luminescence can be divided into categories by duration (fluorescence or phosphorescence) or by the mechanism that creates the light (radioluminescence, electroluminescence, photoluminescence, thermoluminescence, triboluminescence, chemiluminescence, bioluminescence). The prefix identifies the energy source responsible for generating or releasing the light.

Phosphorescence is emission of light from a substance exposed to radiation and persisting as an afterglow after the source of excitation has been removed. Fluorescence, on the other hand, is an almost instantaneous effect, ending within about 10^-8 second after excitation.

magnetic permeability    →   magnetska permeabilnost

Magnetic permeability (μ), also called permeability, is a constant of proportionality that exists between magnetic induction and magnetic field intensity. This constant is equal to approximately μ_o = 1.257×10^-6 H/m in a vacuum.

Magnetic permeability is often expressed in relative, rather than in absolute, terms. If μ represents the permeability of the substance in question, then the relative permeability, μ_r, is given by: