CHEMISTRY GLOSSARY

Ostwald’s viscometer    →   Ostwaldov viskozimetar

Ostwald viscometer, also known as U-tube viscometer or capillary viscometer is a device used to measure the viscosity of the liquid with a known density. The method of determining viscosity with this instrument consists of measuring the time for a known volume of the liquid (the volume contained between the marks A and B) to flow through the capillary under the influence of gravity. Ostwald viscometers named after the German chemist Wilhelm Ostwald (1853-1932).

The instrument must first be calibrated with materials of known viscosity such as pure (deionized) water. Knowing the value of viscosity of one liquid, one can calculate the viscosity of other liquid.

where η₁ and η₂ are viscosity coefficients of the liquid and water, and ρ₁ and ρ₂ are the densities of liquid and water, respectively.

polymer    →   polimer

Polymer is a substance composed of molecules of high relative molecular mass (molecular weight), the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass (monomers). In most cases the number of monomers is quite large and is often not precisely known. A single molecule of a polymer is called a macromolecule. Polystyrene is light solid material obtained by polymerisation of styrene (vinyl benzene).

potassium    →   kalij

Potassium was discovered by Sir Humphry Davy (England) in 1807. The origin of the name comes from the Arabic word qali meaning alkali (the origin of the symbol K comes from the Latin word kalium). It is soft, waxy, silver-white metal. Fresh surface has silvery sheen. Quickly forms dull oxide coating on exposure to air. Reacts strongly with water. Reacts with water to give off flammable gas. Reacts violently with oxidants. Occurs only in compounds. Potassium is found in minerals like carnallite [(KMgCl₃)·6H₂O] and sylvite (KCL). Pure metal is produced by the reaction of hot potassium chloride and sodium vapours in a special retort. Used as potash in making glass and soap. Also as saltpetre, potassium nitrate (KNO₃) to make explosives and to colour fireworks in mauve. Vital to function of nerve and muscle tissues.

Prandtl number    →   Prandtlova značajka

Prandtl number (Pr) is a dimensionless quantity used in fluid mechanics, defined by

where η is viscosity, ρ is density, and a is thermal diffusivity.

Rayleigh number    →   Rayleighova značajka

Rayleigh number (Ra) is a dimensionless quantity used in fluid mechanics, defined by

where l is length, g is acceleration of gravity, α is cubic expansion coefficient, T is temperature, ρ is density, η is viscosity, and a is thermal diffusivity.

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

Reynolds number    →   Reynoldsova značajka

Reynolds number (Re) is a dimensionless quantity used in fluid mechanics, defined by

where ρ is density, v is velocity, l is length, and η is viscosity.

rhenium    →   renij

Rhenium was discovered by Walter Noddack, Ida Tacke and Otto Berg (Germany) in 1925. The origin of the name comes from the Latin word Rhenus meaning river Rhine. It is rare and costly, dense, silvery-white metal. Tarnishes in moist air. Resists corrosion and oxidation. Dissolves in nitric and sulfuric acids. Has a very high melting point. Rhenium is found in small amounts in gadolinite and molybdenite. Mixed with tungsten or platinum to make filaments for mass spectrographs. Its main value is as a trace alloying agent for hardening metal components that are subjected to continuous frictional forces.

ribonucleic acid    →   ribonukleinska kiselina

Ribonucleic acid is a complex organic compound in living cells that is concerned with protein synthesis. Plays an intermediary role in converting the information contained in DNA into proteins. RNA carries the genetic information from DNA to those parts of the cell where proteins are made. Some viruses store their genetic information as RNA not as DNA.

Ribonucleic acid is a similar molecule to DNA but with a slightly different structure.

The structural difference with DNA is that RNA contains a -OH group both at the 2' and 3' position of the ribose ring, whereas DNA (which stands, in fact, for deoxy-RNA) lacks such a hydroxy group at the 2' position of the ribose. The same bases can be attached to the ribose group in RNA as occur in DNA, with the exception that in RNA thymine does not occur, and is replaced by uracil, which has an H-group instead of a methyl group at the C-5 position of the pyrimidine. Unlike the double-stranded DNA molecule, RNA is a single-stranded molecule.

The three main functionally distinct varieties of RNA molecules are: (1) messenger RNA (mRNA) which is involved in the transmission of DNA information, (2) ribosomal RNa (rRNA) which makes up the physical machinery of the synthetic process, and (3) transfer RNA (tRNA) which also constitutes another functional part of the machinery of protein synthesis.

salt water    →   slana voda

Salt water is the water of the sea and the ocean. This water contains a relatively high percentage of dissolved salt (about 35 g of salt per 1 000 g of sea water.). About 90 % of that salt would be sodium chloride, or ordinary table salt.

The salinity of ocean water varies. It is affected by such factors as melting of ice, inflow of river water, evaporation, rain, etc.