CHEMISTRY GLOSSARY

nucleotide    →   nukleotid

Nucleotides are the components that made up nucleic acids. They have three major components: the first component is a nitrogenous base, which is derivative of one of two parent compounds, pyrimidine or purine; the second is a pentose, or five carbon sugar group; the third is a unit of phosphate. Each group of three nucleotides in a gene is known as a codon. Whenever the phosphate group is not present, a nucleotide becomes a nucleoside.

octet rule    →   pravilo okteta

Octet rule states that the chemical properties of the elements repeat on a regular basis with increasing atomic mass, and that the chemical properties of each eight element are similar. Since the inert gases, with the exception of helium have eight electrons in their outer shells, this stable electronic configuration is called the octet rule. In chemical reactions atoms of elements tend to react in such a way as to achieve the electronic configuration of the inert gas nearest to them in the periodic table. There are a number of exceptions to the octet rule.

organic    →   organski

1. Organic refers to any chemical compound based on carbon (C) with the exception of some of the simple compounds of carbon, such as carbon dioxide, which are frequently classified as inorganic compounds. Additional elements that are commonly found in organic compounds are hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P) and sulfur (S).

2. Organic or organically-grown foods are grown or raised without synthetic fertilizers, pesticides, growth stimulators, or antibiotics and other drugs. Pests are controlled by cultivation techniques and the use of pesticides derived from natural sources and the use of natural fertilizers. In addition, organically grown foods must also be stored without the use of chemicals such as artificial additives and preservatives, and without food irradiation.

pH    →   pH

pH is a convenient measure of the acid-base character of a solution, usually defined by

where c(H⁺) is the concentration of hydrogen ions in moles per litre. The more precise definition is in terms of activity rather than concentration.

A solution of pH 0 to 7 is acid, pH of 7 is neutral, pH over 7 to 14 is alkaline.

plastic    →   plastika

Plastic is a material that can be shaped by the application of heat or pressure. Most are based on synthetic polymers although some are the product of natural substances (such as cellulose derivatives, but excluding the rubbers.). They are usually light and permanent solids, being also heat and electric isolators. If the materials soften again when reheated, they are said to be thermoplastic. If, after fashioning, they resist further applications of heat, they are said to be thermoset.

polarography    →   polarografija

Polarography is a volumetric technique which is based on a diffusion controlled analyte travel to the surface of dropping mercury electrode (DME). The surface of the working electrode (dropping mercury electrode) is constantly renewed under dropping conditions and, thus, the conditions under which reaction takes place are readily reproducible. Depolarisation potential enables identification of ions present in the solution, and by measuring the diffusion current their concentration is calculated. Polarography was discovered in 1922 by the Czech chemist Jaroslav Heyrovský (1890-1967).

potentiometric titration    →   potenciometrijska titracija

Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume. Types of potentiometric titrations for the determination of analytes in photoprocessing solutions include acid-base, redox, precipitation, and complexometric.

Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.

A titration curve has a characteristic sigmoid curve. The part of the curve that has the maximum change marks the equivalence point of the titration. The first derivative, ΔE/ΔV, is the slope of the curve, and the endpoint occurs at the volume, V', where ΔE/ΔV has the maximum value.

redox titration    →   redoks-titracija

Redox titration (oxidation-reduction titration) is a titration based on a redox reaction. For example, iron in water can be determined by converting dissolved iron to Fe²⁺ and titrating the solution with potassium permanganate (KMnO₄), a powerful oxidising agent.

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.

salinity    →   salinitet

Salinity (S) is a measure of the quantity of dissolved salts in seawater. It is formally defined as the total amount of dissolved solids in seawater in parts per thousand (‰) by weight when all the carbonate has been converted to oxide, the bromide and iodide to chloride, and all organic matter is completely oxidized.

Chlorinity is the oldest of the salinity measures considered and is still a corner-stone in the study of dissolved material in seawater. Based on the principle of constant relative proportions it provides a measure of the total amount of dissolved material in seawater in terms of the concentration of halides. The relationship between chlorinity (Cl) and salinity as set forth in Knudsen’s tables is

In 1962, however, a better expression for the relationship between total dissolved salts and chlorinity was found to be

Practical Salinity (S_P) was introduced as a replacement for Chlorinity. Practical Salinity is is relatively easy to measure using standard conductometers, measurements are more precise and less time consuming than measurements of Chlorinity and accurate measurements can even be made in situ. Practical salinity S_P is defined on the Practical Salinity Scale of 1978 (PSS-78) in terms of the conductivity ratio K₁₅ which is the electrical conductivity of the sample at temperature t₆₈ = 15 °C and pressure equal to one standard atmosphere, divided by the conductivity of a standard potassium chloride (KCl) solution at the same temperature and pressure. The mass fraction of KCl in the standard solution is 0.0324356 (32.4356 g of KCl in 1 kg of solution).

Note that Practical Salinity is a unit-less quantity. Though sometimes convenient, it is technically incorrect to quote Practical Salinity in "psu". For most purposes one can assume that the psu and the ‰, are synonymous.

The global average salinity of ocean waters is about 35 ‰, that is, about 35 g of solid substances are dissolved in 1 kg of seawater.