CHEMISTRY GLOSSARY

white light    →   bijela svjetlost

White light is a mixture of lights of all colours. If white light is passed through a glass prism or an optical lattice, it is separated into several colours (the visible light spectrum).

zeotrope    →   zeotrop

Zeotrope is a liquid mixture that shows no maximum or minimum when vapour pressure is plotted against the composition at a constant temperature. (See Azeotrope)

Zimmermann-Reinhardt’s reagent    →   Zimmermann-Reinhardtov reagens

Zimmermann-Reinhardt’s reagent is a mixture of manganese(II) sulphate, sulphuric acid and phosphorus acid. It is used for preventing oxidation of chloride ion while titrating iron(II) ion with permanganate solution.

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.

hexagonal close-packed structure    →   heksagonska gusta slagalina

In a hexagonal close-packed (hcp) arrangement of atoms, the unit cell consists of three layers of atoms. The top and bottom layers (a) contain six atoms at the corners of a hexagon and one atom at the center of each hexagon. The middle layer (b) contains three atoms nestled between the atoms of the top and bottom layers, hence, the name close-packed. The hexagonal close packed structure can be made by piling layers in the a-b-a-b-a-b... sequence.

hexagonal crystal system    →   heksagonski kristalni sustav

Hexagonal crystal system is based on four crystallographic axes. The system of crystallographic axes of the hexagonal crystal system consists of three equivalent horizontal (equatorial) axes of which the positive ends make an angle of 120°. These axes are sometimes denoted as a, b and d axes. The fourth axis is (c) is perpendicular to and shorter or longer than the other three.

hydrogen    →   vodik

Hydrogen was discovered by Sir Henry Cavendish (England) in 1766. The origin of the name comes from the Greek words hydro and genes meaning water and generate. It is colourless, odourless gas, burns and forms explosive mixtures in air. Reacts violently with oxidants. Hydrogen is the most abundant element in the universe. Commercial quantities of hydrogen are produced by reacting superheated steam with methane or carbon. In lab work from reaction of metals with acid solutions or electrolysis. Most hydrogen is used in the production of ammonia and in metal refining. Also used as fuel in rockets. Its two heavier isotopes (deuterium and tritium) used respectively for nuclear fusion.

invert sugar    →   invertni šećer

Invert sugar is a mixture of equal parts of glucose and fructose resulting from the hydrolysis of sucrose (saccharose). The name stemming from the fact that it rotates of plane polarized light in the opposite direction of sucrose. Sucrose is dextrorotatory - it rotates polarized light clockwise ([α]_D = +66.5°). Invert sugar rotates the plane of the polarized light counterclockwise ([α]_D = -22°) due to the strongly levorotatory nature of fructose ([α]_D = -92°).

Homemade artificial honey (invert sugar syrup): Dissolve two parts of household sugar (1 kg) with stirring in one part of water (0.5 kg) in a saucepan over low heat. Add 1 g of citric acid or the juice of one lemon to the mixture. Bring the ingredients to a slow boil. It can take anywhere between 15 minutes to 1 hour. The end result is sticky, golden syrup. Let it sit at room temperature until it is cool.

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

lactose    →   laktoza

Lactose (milk sugar) is a disaccharide comprising one glucose molecule linked to a galactose molecule by an β(1→4)-glycosidic linkage. Lactose has a beta acetal. Lactose is manufactured by the mammary gland and occurs only in milk (from 4 % to 7 %). Lactose intolerance is a common medical condition that results in diarrhea, abdominal pain, and flatulence and is caused by reduced or absent activity of enzyme lactase.

Like cellobiose and maltose, lactose is a reducing sugar. All reducing sugar undergo mutarotation in aqueous solution. The equilibrium mixture at 20 °C is composed of 62.7 % β-lactose (β-D-galactopyranosyl-(1→4)-β-D-glucopyranose) and 37.3 % α-lactose (β-D-galactopyranosyl-(1→4)-α-D-glucopyranose).