CHEMISTRY GLOSSARY

precision balance    →   tehnička vaga

Precision balances typically display results from three to one decimal places (0.001 g up to 0.1 g). The readability precision balances are reduced when compared to analytical balances but, precision balances accommodate higher capacities (up to several kilograms). In its traditional form, it consists of a pivoted horizontal lever of equal length arms, called the beam, with a weighing pan, also called scale, suspended from each arm.

In electronic top pan, or toploader balances, mass is determined not by mechanical deflection but by electronically controlled compensation of an electric force. The signal generated enables the mass to be read from a digital display. The mass of the empty container can be stored in the balance’s computer memory and automatically deducted from the mass of the container plus its contents.

redox potential    →   redoks potencijal

Redox potential is the potential of a reversible oxidation-reduction electrode measured with respect to a reference electrode, corrected to the hydrogen electrode, in a given electrolyte.

redox reaction    →   redoks-reakcija

Redox reaction is an oxidation-reduction reaction is a reaction in which one or more electrons are transferred. When an atom, ion, or molecule loses one or more electrons, it is oxidised. When an atom, ion, or molecule gains one or more electrons, it is reduced.

reducing agent    →   redukcijsko sredstvo

Reducing agent may be defined in various ways, depending upon the context in which the phrase is used. In broad terms it is often taken to mean a chemical which can act as an electron donor. Thus, in the reaction:

the zinc is being reduced (gaining electrons) by reaction with the iron cations; the Fe²⁺ in this instance is acting as a reducing agent.

resonance    →   rezonancija

Resonance is a stabilising quality of certain molecules that can be represented by considering the electron distribution in an ion or molecule as a composite of two or more forms, in those cases where a single form is an inadequate representation; for example, benzene and the carbonate ion. A various canonical structures can be drawn to show how electron delocalisation will explain the discrepancy, the difference in electron density

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.

semiconductor    →   poluvodič

Semiconductor is a material in which the highest occupied energy band (valence band) is completely filled with electrons at T = 0 K, and the energy gap to the next highest band (conduction band) ranges from 0 to 4 or 5 eV. With increasing temperature electrons are excited into the conduction band, leading to an increase in the electrical conductivity.

silicon    →   silicij

Silicon was discovered by Jöns Jacob Berzelius (Sweden) in 1824. The origin of the name comes from the Latin word silicis meaning flint. Amorphous form of silicon is brown powder; crystalline form has grey metallic appearance. Solid form unreactive with oxygen, water and most acids. Dissolves in hot alkali. Silica dust is a moderately toxic acute irritant. Silicon makes up major portion of clay, granite, quartz and sand. Commercial production depends on a reaction between sand (SiO₂) and carbon at a temperature of around 2200 °C. Used in glass as silicon dioxide (SiO₂). Silicon carbide (SiC) is one of the hardest substances known and used in polishing. Also the crystalline form is used in semiconductors.

silver coulometer    →   srebrni kulometar

Silver coulometer consists of a platinum vessel which acts as a cathode and contains a solution of pure silver nitrate as an electrolyte (c(AgNO₃) = 1 mol/L). A rod of pure silver enclosed in a porous pot acts as the anode. The current density at the anode should not exceed 0.2 Acm^-2. After electrolysis, the electrolyte is taken out and the platinum vessel is washed, dried and weighed. The increase in the weight gives the amount of silver deposited (96500 C of electricity deposits 107.88 g of silver). From the mass of the silver deposited, the coulomb involved in the reaction can be calculated.

square planar molecular geometry    →   kvadratna planarna geometrija molekule

Square planar is a molecular shape that results when there are four bonds and two lone pairs on the central atom in the molecule. An example of a square planar molecule is xenon tetrafluoride (XeF₄). This molecule is made up of six equally spaced sp³d² (or d²sp³) hybrid orbitals arranged at 90° angles. The shape of the orbitals is octahedral. Two orbitals contain lone pairs of electrons on opposite sides of the central atom. The remaining four atoms connected to the central atom give the molecule a square planar shape.