CHEMISTRY GLOSSARY

gas    →   plin

Gas is a state of matter, in which the mollecules move freely and consequently the entire mass tends to expand indefinitely, occupying the total volume of any vessel into which it is introduced. Gases follow, within considerable degree of fidelity, certain laws relating their conditions of pressure, volume and temperature. Gases mix freely with each other, and they can be liquefied through compression or temperature reduction.

gas washing bottle    →   boca ispiralica

Gas washing bottle or Drechsel bottle provide an inexpensive but effective method for washing or drying gases. The gas enters the bottle through the top of the central vertical tube, the lower end of which is below the surface of the washing medium. To maximize surface area contact of the gas to the liquid, a gas stream is slowly blown into the vessel through the fritted glass tip so that it breaks up the gas into many tiny bubbles. After bubbling through the medium, the gas rises to the top and exits through the side tube. It is named after the German chemist Edmund Drechsel (1843-1897).

Geiger counter    →   Geigerov brojač

Geiger counter (Geiger-Muller counter) is a device used to detect and measure ionising radiation. It consists of a tube containing a low-pressure gas (usually argon or neon with methane) and a cylindrical hollow cathode through the centre of which runs a fine-wire anode. A potential difference of about 1 000 V is maintained between the electrodes. An ionising particle or photon passing through a window into the tube will cause an ion to be produced and the high potential will accelerate it towards its appropriate electrode, causing an avalanche of further ionisations by collision. The consequent current pulses can be counted in electronic circuits or simply amplified to work a small loudspeaker in the instrument. It was first devised in 1908 by the German physicist Hans Geiger (1882-1945). Geiger and W. Muller produced an improved design in 1928.

glycogen    →   glikogen

Glycogen (animal starch) is a polysaccharide that serves the same energy storage function in animals that starch serves in plants. Dietary carbohydrates not needed for immediate energy are converted by the body to glycogen for long term storage (principally in muscle and liver cells). Like amylopectin found in starch, glycogen is a polymer of α(1→4)-linked subunits of glucose, with α(1→6)-linked branches. Glycogen molecules are larger than those of amylopectin (up to 100 000 glucose units) and contain even more branches. Branch points occur about every 10 residues in glycogen and about every 25 residues in amylopectin. The branching also creates lots of ends for enzyme attack and provides for rapid release of glucose when it is needed.

hafnium    →   hafnij

Hafnium was discovered by Dirk Coster (Denmark) and Georg Karl von Hevesy (Hungary) in 1923. The origin of the name comes from the Latin name Hafnia meaning Copenhagen. It is silvery, ductile metal. Exposed surfaces form oxide film. Resists alkalis and acids (except HF). Toxic. Metal ignites and burns readily. Hafnium is obtained from mineral zircon or baddeleyite. Used in reactor control rods because of its ability to absorb neutrons.

helium    →   helij

Helium was discovered by Pierre Jules César Janssen (France) and Sir William Ramsay (Scotland) in 1868. The origin of the name comes from the Greek word helios meaning sun. It is light, odourless, colourless inert gas. Second most abundant element in the universe. Helium is found in natural gas deposits from wells in Texas, Oklahoma and Kansas. Used in balloons, deep sea diving and welding. Also used in very low temperature research.

high fructose corn syrup    →   visoko fruktozni kukuruzni sirup

High fructose corn syrup (HFCS) is commonly used in place of sugar in foods and drinks. Corn starch is hydrolyzed to glucose, which is then treated with glucose isomerase to produce a fructose-rich mixture. HFCS is available in a number of forms, named according to the percentage of fructose they contain, HFCS-55 for instance contains 55 % fructose and 45 % glucose. The enhanced sweetness, low cost and ease of use are the main reasons why manufacturers now prefer to use high fructose corn syrup instead of sugar.

hydrolysis    →   hidroliza

Hydrolysis is a chemical reaction in which water reacts with another substance to form two or more new substances. This involves ionisation of the water molecule, as well as splitting of the compound hydrolysed, e.g.

Examples are conversion of starch to glucose by water in the presence of suitable catalysts and a reaction of the ions of a dissolved salt to form various products, such as acids, complex ions, etc.

kinetic energy    →   kinetička energija

Kinetic energy (E_k) is associated with the state of motion of a body. It is a scalar property and defined to be

Kinetic energy is most clearly exhibited in gases, in which molecules have much greater freedom of motion than in liquids and solids.

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