CHEMISTRY GLOSSARY

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

gasoline    →   motorni benzin

Gasoline is a complex mixture of volatile hydrocarbons that may have between 5 to 12 carbons. The major components are branched-chain paraffins, cycloparaffins, and aromatics. Gasoline is most often produced by the fractional distillation of crude oil as the fraction of hydrocarbons in petroleum boiling between 30 °C and 200 °C. The quality of a fuel is measured with its octane number. Octane number is the measure of the resistance of gasoline against detonation or preignition of the fuel in the engine. The higher the octane number, the more compression the fuel can withstand before detonating. The octane number is determined by comparing the characteristics of a gasoline to isooctane with good knocking properties (octane number of 100) and heptane with bad (octane number of 0).

Kjeldahl’s method    →   Kjeldahlov postupak

Kjeldahl’s method is an analytical method for determination of nitrogen in certain organic compounds. The method was developed by the Danish chemist Johan Kjeldahl (1849-1900).

It involves addition of a small amount of anhydrous potassium sulphate to the test compound, followed by heating the mixture with concentrated sulphuric acid, often with a catalyst such as copper sulphate. As a result ammonia is formed. After alkalyzing the mixture with sodium hydroxyde, the ammonia is separated by distillation, collected in standard acid, and the nitrogen determined by back-titration.

1. Kjeldahl flask for decomposition (500 ml – macro or 100 ml - micro)
2. funnel for alkaline solution
3. Wagner tube (drop catcher)
4. condenser
5. absorption flask with known volume of standard acid

purification    →   pročišćavanje

Purification is the physical or chemical process of removing contaminants from a compound. The physical processes may include sublimation, distillation, filtration, crystallisation, or extraction. The chemical processes may involve formation of a derivative, purification of the derivative and recovery of the original material in a pure form of the derivative.

nitrogen    →   dušik

Nitrogen was discovered by Daniel Rutherford (Scotland) in 1772. The origin of the name comes from the Greek words nitron genes meaning nitre and forming and the Latin word nitrum (nitre is a common name for potassium nitrate, KNO₃). It is colourless, odourless, generally inert gas. Minimally reactive at room temperature. A component of many organic and inorganic compounds. Makes up about 78 % of earth’s atmosphere. Nitrogen is obtained from liquid air by fractional distillation. Primarily to produce ammonia and other fertilizers. Also used in making nitric acid, which is used in explosives. Also used in welding and enhanced oil recovery.

oxygen    →   kisik

Oxygen was discovered by Joseph Priestley (England) in 1774. The origin of the name comes from the Greek words oxy genes meaning acid and forming (acid former). It is colourless, odourless gas; pale blue liquid. Extremely reactive. Forms oxides with nearly all other elements except noble gases. It is the most abundant element in the earth’s crust and makes up almost 21 % of the atmosphere. Oxygen is obtained primarily from liquid air by fractional distillation. Small amounts are made in the laboratory by electrolysis of water. Used in steel making, welding and supporting life. Naturally occurring ozone (O₃) in the upper atmosphere shields the earth from ultraviolet radiation.

pyrolysis    →   piroliza

Pyrolysis is a disintegration of some matter under the influence of heat for example dry distillation.

Soxhlet extractor    →   Soxhletov ekstraktor

Soxhlet extractor is a laboratory apparatus designed to extract substances with a low solubility in the extracting solvent. The method described by the German chemist Franz von Soxhlet (1848-1926) in 1879 is the most commonly used example of a semi-continuous method applied to extraction of lipids from foods. In the Soxhlet extractor, the sample soaks in hot solvent that is periodically siphoned off, distilled and returned to the sample. During each cycle, a portion of the non-volatile compound dissolves in the solvent. After many cycles the desired compound is concentrated in the distillation flask. The solvent in the flask is then evaporated and the mass of the remaining lipid is measured.

tar    →   katran

Tar is a brown or black bituminous material, liquid or semi-solid in consistency, gained as a product of dry distillation of natural fuels like wood, or other organic materials.

Wagner tube    →   Wagnerova cijev

Wagner tube or drop catcher impedes the movement of distillate drops from the distillation flask to the condensing chamber.