CHEMISTRY GLOSSARY

tetragonal crystal system    →   tetragonski kristalni sustav

Minerals of the tetragonal crystal system are referred to three mutually perpendicular axes. The two horizontal axes are of equal length, while the vertical axis is of different length and may be either shorter or longer than the other two.

thermochemical equation    →   termokemijska jednadžba

Thermochemical equation is a compact equation representing a chemical reaction that describes both the stoichiometry and the energetics of the reaction. For example, the thermochemical equation

means When one mole of gaseous methane is burned in two moles of oxygen gas, one mole of carbon dioxide gas and 2 moles of steam are produced, and 2 220 kJ of heat are released.

thorium    →   torij

Thorium was discovered by Jöns Jakob Berzelius (Sweden) in 1828. Named after Thor, the mythological Scandinavian god of war. It is heavy, grey, soft, malleable, ductile, radioactive metal. Tarnishes in air; reacts with water. Reacts violently with oxidants. Thorium is found in various minerals like monazite and thorite. Used in making strong alloys. Also in ultraviolet photoelectric cells. It is a common ingredient in high-quality lenses. Bombarded with neutrons make uranium-233, a nuclear fuel.

tin    →   kositar

Tin has been known since ancient times. The origin of the name comes from the Latin word stannum meaning tin. It is silvery-white, soft, malleable and ductile metal. Exposed surfaces form oxide film. Resists oxygen and water. Dissolves in acids and bases. Organic tin compounds may be highly toxic. Tin is principally found in the ore cassiterite (SnO₂) and stannine (Cu₂FeSnS₄). Used as a coating for steel cans since it is non-toxic and non-corrosive. Also in solder (33 %Sn:67 %Pb), bronze (20 %Sn:80 %Cu) and pewter. Stannous fluoride (SnF₂), a compound of tin and fluorine is used in some toothpaste.

U-tube    →   U-cijev

U-tube filled with a sodium hydroxide is used for a cleaned and dried gas.

U-tube filled with a 1 mol dm^-3 aqueous potassium nitrate solution is used as a permanent salt bridge.

U-tube is a device used for water electrolysis, for laboratory hydrogen and oxygen obtaining.

U-tube manometer    →   U-manometar

U-tube manometer contains water or mercury in a U-shaped tube, and is usually used to measure gas pressure. One end of the U tube is exposed to the unknown pressure field (P) and the other end is connected to a reference pressure source (usually atmospheric pressure) (P_ref), shown in the schematic below.

If fluid C is the atmosphere, fluid B is the liquid in the U tube (e.g. water or mercury), and fluid A is a gas, then we can assume that ρB >> ρA, ρC. The pressure contributed by the weight of gas within the U tube can therefore be neglected. The gage pressure of the gas can be approximated by,

unsaturated fatty acid    →   nezasićena masna kiselina

Unsaturated fatty acid is a fatty acid whose carbon chain can absorb additional hydrogen atoms. Their carbon chain has one or more double or triple valence bond per molecule. The most important of these are:

uranium    →   uranij

Uranium was discovered by Martin Heinrich Klaproth (Germany) in 1789. Named after the planet Uranus. It is silvery-white, dense, ductile, malleable, radioactive metal. Resists alkalis; tarnishes in air; attacked by steam and acids. Radiotoxic. Uranium occurs in many rocks, but in large amounts only in such minerals as pitchblende and carnotite. For many centuries it was used as a pigment for glass. Now it is used as a fuel in nuclear reactors and in bombs.

volumetric pipette    →   prijenosna pipeta

Volumetric pipettes (transfer or belly pipette) are used in volumetric analysis, when there is a need for taking exact smaller volume of a sample solution or reagent. The upper tube of volumetric pipette has a ringlike marking (mark) which marks its calibrated volume. Pipettes calibrated to deliver (TD or Ex) the indicated volume. By sucking in (with mouth, propipette or a water pump) the liquid is pulled in a little bit above the mark and the opening of the pipet is closed with a forefingertip. Outer wall of pipet is wiped and, with a slight forefinger loosening, the liquid is released until it reaches the mark. Mark must figure as a tangent on a lower edge of the liquid meniscus. A pipette is emptied out by lifting the forefinger off and letting the liquid flow out of the pipette freely. After another 15 s and the tip of the pipette is pulled onto the inner wall of the vessel. It is absolutely forbidden to blow out the contents of the pipette.

wash bottle    →   boca štrcaljka

Plastic wash bottle is a squeeze bottle made of low density polyethylene (LDPE) whose contents can be forced out through a narrow hole at the top by squeezing the bottle.

Glass wash bottle is a bottle fitted with two glass tubes pass through the cap, so that on blowing into one of the tubes a stream of water issuing from the other may be directed upon anything to be washed or rinsed, as a precipitate upon a filter.