CHEMISTRY GLOSSARY
composition of ocean water → sastav oceanske vode
The proportions of the major constituents of ocean water are almost constant throughout the world. Salinity (total salt content) and the concentrations of individual chemical constituents in sea wateris given the units psu (practical salinity units). For most purposes one can assume that the new unit, psu, and the older unit, ‰, are synonymous.
The average composition of the ocean water is as shown on the following table.
| Constituent | Percentage of total salt |
|---|---|
| Chlorine | 55.3 % |
| Sodium | 30.8 % |
| Magnesium | 3.7 % |
| Sulphur | 2.6 % |
| Calcium | 1.2 % |
| Potassium | 1.1 % |
cross-linking → umrežavanje
Cross-linking is an attachment of two chains of polymer molecules by bridges, composed of either an element, a group, or a compound, that join certain carbon atoms of the chains by primary chemical bonds, as indicated in the schematic diagram
Cross-linking occurs in nature in substances made up of polypeptide chains that are joined by the disulfide bonds of the cysteine residue, as in keratins or insulin. Cross-linking can be artificially effected, either adding a chemical substance (cross-linking agent), or by subjecting the polymer to high-energy radiation. Examples are: vulcanisation of rubber with sulphur, cross-linking of polystyrene with divinylbenzene, or cross-linking of polyethylene by means of high-energy radiation.
Cross-linking has the effect of changing a plastic from thermoplastic to thermosetting. Thus, it also increases strength, heat and electrical resistance, and especially resistance to solvents and other chemicals.
dissociation → disocijacija
Dissociation is the process by which a chemical combination breaks up into simpler constituents as a result of either added energy (dissociated by heat), or the effect of a solvent on a dissolved polar compound (electrolytic dissociation). It may occur in the gaseous, solid, or liquid state, or in a solution.
An example of dissociation is the reversible reaction of hydrogen iodide at high temperatures
The term dissociation is also applied to ionisation reactions of acids and bases in water. For example
which is often regarded as a straightforward dissociation into ions
fractional crystallisation → frakcijska kristalizacija
Fractional crystallisation is a method of separating a mixture of soluble solids by dissolving them in a suitable hot solvent and then lowering the temperature slowly. The least soluble component will crystallise out first, leaving the other components in the solution. By controlling the temperature, it is sometimes possible to remove each component in turn.
insoluble substance → netopljiva tvar
Insoluble substance is a substance that does not dissolve in a solvent to give a reasonable concentration (e.g. chalk is insoluble in water).
distilled water → destilirana voda
Distilled water is water purified by distillation so as to free it from dissolved salts and other compounds. Distilled water in equilibrium with the carbon dioxide in the air has conductivity of about 0.8×10-6 S cm-1. Repeated distillation in vacuum can bring conductivity down to 0.043×10-6 S cm-1 at 18 °C. The limiting conductivity is due to self ionisation
extraction → ekstrakcija
Extraction is the separation of a component from its mixture by selective solubility. When a solution of one substance in one solvent is brought in with another solvent dissolved substance will distribute between the two solutants because of different solubility. Extraction is an efficient and fast method used for separating and concentrating matters. Extraction is best done several times in a succession, with smaller amount of solvent in it the matter is better dissolved. For example, caffeine can be separated from coffee beans by washing the beans with supercritical fluid carbon dioxide; the caffeine dissolves in the carbon dioxide, but flavour compounds do not. Vanillin can be extracted from vanilla beans by shaking the beans with an organic solvent, like ethanol.
Henry’s law → Henryjev zakon
Henry’s law was discovered in 1801 by the British chemist William Henry (1775-1836). At a constant temperature the mass of gas dissolved in a liquid at equilibrium is proportional to the partial pressure of the gas. It applies only to gases that do not react with the solvent.
where pi is the partial pressure of component i above the solution, xi is its mole fraction in the solution, and Kx is the Henry’s law constant (a characteristic of the given gas and solvent, as well as the temperature).
Citing this page:
Generalic, Eni. "Otapalo." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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