CHEMISTRY GLOSSARY

spin    →   spin

Spin is the intrinsic angular momentum of an elementary particle, or system of particles such as nucleus, that is also responsible for the magnetic moment; or, a particle or nucleus possessing such a spin. The spins of nuclei have characteristic fixed values. Pairs of neutrons and protons align to cancel out their spins, so that nuclei with an odd number of neutrons and/or protons will have a net non-zero rotational component characterized by a non-zero quantum nuclear spin number.

Stern-Gerlach experiment: a beam of silver atoms is split into two beams when it traverses a nonuniform magnetic field. Atoms with spin quantum number m_s=+1/2 follow one trajectory, and those with m_s=+1/2 follow another.

supercritical fluid extraction    →   superkritična fluidna ekstrakcija

Supercritical fluid extractions (SFE) have solvating powers similar to liquid organic solvents, but with higher diffusivities, lower viscosity, and lower surface tension. The main advantages of using supercritical fluids for extractions is that they are inexpensive, contaminant free, and less costly to dispose safely than organic solvents. For non-destructive isolation choose SFE, which is simply the best technology for sensitive raw materials. For these reasons supercritical carbon dioxide (scCO₂) is the reagent used to extract caffeine from coffee and tea. Its gaslike behavior allows it to penetrate deep into the green coffee beans, and it dissolves from 97 % to 99 % of the caffeine present.

teflon    →   teflon

Teflon is a DuPont Company trademark for polytetrafluoroethylene (PTFE). It was discovered in 1938 by R. J. Plunkett. Teflon has the lowest coefficient of friction of any solid material known to man. It is also used as a non-stick coating for pans and other cookware. Teflon is very unreactive, and so is often used in containers and pipework for reactive chemicals. Its melting point is 327 °C.

terbium    →   terbij

Terbium was discovered by Carl Gustaf Mosander (Sweden) in 1843. Named after Ytterby, a village in Sweden. It is soft, ductile, silvery-grey, rare earth metal. Oxidizes slowly in air. Reacts with cold water. Terbium is found with other rare earths in monazite sand. Other sources are xenotime and euxenite, both of which are oxide mixtures that can contain up to 1 % terbium. It is used in modest amounts in special lasers and solid-state devices.

Torricelli, Evangelista    →   Torricelli, Evangelista

Evangelista Torricelli (1852-1908) is Italian physicist and mathematician. He became the first scientist to create a sustained vacuum and to discover the principle of a barometer. He filled a tube three feet long, and hermetically closed at one end, with mercury and set it vertically with the open end in a basin of mercury, taking care that no air-bubbles should get into the tube. The column of mercury invariably fell to about twenty-eight inches, leaving an empty space above its level. He discovered that the variation of the height of the mercury from day to day was caused by changes in the atmospheric pressure. He also constructed a number of large objectives and small, short focus, simple microscopes.

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,

ultraviolet light    →   ultraljubičasto svjetlo

Ultraviolet light (UV light or UV radiation) is an electromagnetic radiation with a wavelength longer than that of x-rays, but shorter than that of visible light. Ultraviolet light can break some chemical bonds and cause cell damage.

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.

water hardness    →   tvrdoća vode

Hardness is defined as the concentrations of calcium and magnesium ions expressed in terms of calcium carbonate. These minerals in water can cause some everyday problems. They react with soap and produce a deposit called soap curd that remains on the skin and clothes and, because it is insoluble and sticky, cannot be removed by rinsing.

Hard water may also shorten the life of plumbing and water heaters. When water containing calcium carbonate is heated, a hard scale is formed that can plug pipes and coat heating elements. Scale is also a poor heat conductor. With increased deposits on the unit, heat is not transmitted to the water fast enough and overheating of the metal causes failure. Build-up of deposits will also reduce the efficiency of the heating unit, increasing the cost of fuel.

There are two types of water hardness, temporary and permanent.

Temporary Hardness is due to the bicarbonate ion, HCO₃^-, being present in the water. This type of hardness can be removed by boiling the water to expel the CO₂, as indicated by the following equation:

Permanent hardness is due to calcium and magnesium nitrates, sulphates, and chlorides etc. This type of hardness cannot be eliminated by boiling.