CHEMISTRY GLOSSARY

reversible cell    →   povrativi članak

Reversible cell is an electrical cell the chemical action in which can be reversed by passing through it a current opposite in direction to that generated by the cell.

Bunsen, Robert Wilhem    →   Bunsen, Robert Wilhem

Robert Wilhem Bunsen (1811-1899) is a German chemist who held professorships at Kassel, Marburg and Heidelberg. His early researches on organometallic compound of arsenic cost him an eye in an explosion. Bunsen's most important work was in developing several techniques used in separating, identifying, and measuring various chemical substances. He also improvement chemical battery for use in isolating quantities of pure metals - Bunsen battery.

The essential piece of laboratory equipment that has immortalized the name of Bunsen was not invented by him. Bunsen improved the burner's design, which had been invented by Faraday, to aid his endeavors in spectroscopy. Use of the Bunsen burner in conjunction with a glass prism led to the development of the spectroscope in collaboration with the German physicist Gustav Kirchoff and to the spectroscopic discovery of the elements rubidium (1860) and cesium (1861).

electrode potential    →   elektrodni potencijal

Electrode potential is defined as the potential of a cell consisting of the electrode in question acting as a cathode and the standard hydrogen electrode acting as an anode. Reduction always takes place at the cathode, and oxidation at the anode. According to the IUPAC convention, the term electrode potential is reserved exclusively to describe half-reactions written as reductions. The sign of the half-cell in question determines the sign of an electrode potential when it is coupled to a standard hydrogen electrode.

Electrode potential is defined by measuring the potential relative to a standard hydrogen half cell

The convention is to designate the cell so that the oxidised form is written first. For example

The e.m.f. of this cell is

By convention, at p(H₂) = 101325 Pa and a(H⁺) = 1.00, the potential of the standard hydrogen electrode is 0.000 V at all temperatures. As a consequence of this definition, any potential developed in a galvanic cell consisting of a standard hydrogen electrode and some other electrode is attributed entirely to the other electrode

half-cell    →   polučlanak

Half-cell is a part of galvanic cell in which oxidations or reduction of an element in contact with water or water solution one of its compounds.

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.

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).

battery    →   baterija

Battery a device that converts chemical energy to electrical energy. The process underlying the operation of a battery involves a chemical reaction in which electrons are transferred from one chemical species to another. This process is carried out in two half-reactions, one that involves the loss of electrons and one that involves their gain. The battery is an electrochemical cell divided in two half-cells, and reaction proceeds when these are connected together by an electrically conducting pathway. The passage of electrons from one half-cell to the other corresponds to an electric current. Each half-cell contains an electrode in contact with the reacting species. The electrode which passes electrons into the circuit when battery discharges is called anode and is negative terminal. The electrode which receives electrons is called cathode, and is the battery’s positive terminal. The electrical circuit is completed by an electrolyte, an electrically conducting substance placed between the two electrodes which carriers a flow of charge between them. In wet cells, the electrolyte is a liquid containing dissolved ions, whose motion generates an electrical current; in dry cells the electrolyte is basely solid, for example, a solid with mobile ions or porous solid saturated with an ionic solution.

cadmium coating    →   kadmiranje

Cadmium coating is a galvanic coating of metallic objects with a cadmium layer for corrosion resistance.

nickel    →   nikal

Nickel was discovered by Axel Fredrik Cronstedt (Sweden) in 1751. The origin of the name comes from the German word kupfernickel meaning Devil’s copper or St Nicholas’s (Old Nick’s) copper. It is hard, malleable, silvery-white metal. Soluble in acids, resist alkalis. It can be polished to a lustrous finish. Resists corrosion in air under normal conditions. Nickel is chiefly found in pentlandite [(Ni,Fe)₉S₈] ore. The metal is produced by heating the ore in a blast furnace which replaces the sulfur with oxygen. The oxides are then treated with an acid that reacts with the iron not the nickel. Used in electroplating and metal alloys because of its resistance to corrosion. Also in nickel-cadmium batteries, as a catalyst and for coins.

salt bridge    →   solni most

Salt bridge is a permeable material soaked in a salt solution that allows ions to be transferred from one container to another. The salt solution remains unchanged during this transfer.