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.

proline    →   prolin

Proline has an aliphatic side chain with a distinctive cyclic structure. It is unusual because it is conformationally restricted. The secondary amino (imino) group of proline residues is held in a rigid conformation that reduces the structural flexibility of polypeptide regions containing proline. It is not an essential amino acid, which means that the human body can synthesize it.

• Abbreviations: Pro, P
• IUPAC name: pyrrolidine-2-carboxylic acid
• Molecular formula: C₅H₉NO₂
• Molecular weight: 115.13 g/mol

qualitative analysis    →   kvalitativna analiza

Qualitative analysis involves determining the nature of a pure unknown compound or the compounds present in a mixture. Qualitative inorganic analysis is used to separate and detect cations and anions in a sample substance. According to their properties, cations are usually classified into six groups. Each group has a common reagent which can be used to separate them from the solution.

radioactive series    →   radioaktivni niz

Radioactive series is a sequence of nuclides formed by successive radioactive decays until a stable decay product, the end product, is formed. A famous example of a radioactive series is the decay of uranium, which through a series of steps decays into stable lead.

rare earth elements    →   elementi rijetkih zemalja

Rare earth elements (metals) are the elements scandium (Sc), yttrium (Y), and the lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). These elements got their name from the fact that chemists first isolated them in their oxide forms. These oxides somewhat resemble calcium, magnesium and aluminium oxides, sometimes called common earths. Do you want to know more?

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.

reflux condenser    →   povratno hladilo

Reflux condenser is used for repeated transformation of vapour in liquid in order to prevent the loss due to evaporation.

refractometer    →   refraktometar

Refractometer is an optical device used from measurement of refractive index. A refractometer takes advantage of the fact that light bends as it passes through different materials. It can be used to measure the salinity of water or the amount of sugar in fresh grapes. Refractometers are available with or without automatic temperature compensation (ATC).

When using a conventional saltwater refractometer, a sample is placed on an optical prism in the sample window. As light shines through the sample, it is bent according to the salinity of the water, and casts a shadow on the scale that is visible through the eyepiece. Salinity is read directly through the eyepiece.

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

rhombohedral crystal system    →   romboedarski kristalni sustav

Rhombohedral crystal system is also known as the trigonal system. The crystallographic axes used in this system are of equal length. None of the axes are perpendicular to any other axis.