CHEMISTRY GLOSSARY

analytical balance    →   analitička vaga

Analytical balances are instruments used for precise determining mass of matter. Analytical balances are sensitive and expensive instruments, and upon their accuracy and precision the accuracy of analysis result depends. The most widely used type of analytical balances are balances with a capacity of 100 g and a sensitivity of 0.1 mg. Not one quantitative chemical analysis is possible without usage of balances, because, regardless of which analytical method is being used, there is always a need for weighing a sample for analysis and the necessary quantity of reagents for solution preparation.

The working part of the balance is enclosed in a glass-fitted case. The baseplate is usually of black glass or black slate. The beam has agate knife-edges at its extremes, supporting stirrups from which balance pans are suspended. Another agate or steel knife-edge is fixed exactly in the middle of the beam on its bottom side. This knife-edge faces downwards and supports the beam. When not in use and during loading or unloading of the pans, the balance should be arrested.

The principle of operation of a modern laboratory balance bears some resemblance to its predecessor - the equal arm balance. The older instrument opposed the torque exerted by an unknown mass on one side of a pivot to that of an adjustable known weight on the other side. When the pointer returned to the center position, the torques must be equal, and the weight was determined by the position of the moving weights.

Modern electronic laboratory balances work on the principle of magnetic force restoration. In this system, the force exerted by the object being weighed is lifted by an electromagnet. A detector measures the current required to oppose the downward motion of the weight in the magnetic field.

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.

biogas    →   bioplin

Biogas is a mixture of methane and carbon dioxide resulting from the anaerobic decomposition of such waste materials as domestic, industrial, and agricultural sewage. Methanogenic bacteria carry out the decomposition; these obligate anaerobes produce methane, the main component of biogas, which can be collected and used as an energy source for domestic processes, such as heating, cooking, and lighting.

benzene    →   benzen

Benzene is a colourless liquid hydrocarbon, C₆H₆, b.p. 80 °C. It is now made from petroleum by catalytic reforming (formerly obtained from coal tar). Benzene is the archetypal aromatic compound. It has an unsaturated molecule, yet will not readily undergo addition reactions. On the other hand, it does undergo substitution reactions in which hydrogen atoms are replaced by other atoms or groups.

In 1865, Friedrich August Kekulé purposed the benzene molecule structure as a hexagonal ring which consists of six carbon atoms with alternate carbon-carbon single and carbon-carbon double bond. But such a structure should be highly reactive, and so didn't account for the unreactive nature of benzene. We now know that the best representation for the structure of benzene is indeed, hexagonal, with each C-C bond distance being identical and intermediate between those for a single and double bond. The π-orbitals from each neighbouring carbon atom overlap to form a delocalised molecular orbital which extends around the ring, giving added stability and with it, decreased reactivity. That is the reason the structural formula of benzene represents as a hexagon with a circle in the center which represents the delocalized electrons.

binary solution    →   binarna otopina

Binary solution is a mixture of two liquids that are completely miscible one with another. The boiling point of binary solution depends upon the solution composition and there can be three cases:

1. the boiling points of solutions of all compositions lie between the boiling points of clean liquids

2. the boiling points of solutions of any composition lie above the boiling points of clean liquids

3. the boiling points of solutions of some compositions lie below the boiling points of clean liquids

butane    →   butan

Butane is a gaseous hydrocarbon C₄H₁₀ obtained from petroleum (refinery gas or by cracking higher hydrocarbons). The fourth member of the alkane series, it has a straight chain of carbon atoms and is isomeric with 2-methylpropane, formerly called isobutene. It can easily be liquefied under pressure and is supplied into cylinders for use as a fuel gas. It is also a raw material for making buta-1, 3-diene for synthetic rubber.

carbolineum    →   karbolineum

Carbolineum is a mixture of ingredients of pit coal tar with the boiling point above 270 °C, red-brown oil with tar smell. It is a wood preservative.

electron pair    →   elektronski par

Electron pair is two electrons within one orbital with opposite spins responsible for a chemical bond.

eutectic    →   eutektik

Eutectic is a solid solution consisting of two or more substances and having the lowest freezing point of any possible mixture of these components.

Eutectic point is the lowest temperature at which the eutectic mixture can exist in a liquid phase. A liquid having the eutectic composition will freeze at a single temperature without a change of composition.

fire-damp    →   plin praskavac

Fire-damp is a mixture of two volume parts of hydrogen and one volume part of oxygen which, if set on fire, strongly explodes, the flame giving of a very high temperature (2 000 °C).