CHEMISTRY GLOSSARY

phosphorescence    →   fosforescencija

Phosphorescence is emission of light from a substance exposed to radiation and persisting as an afterglow after the exciting energy has been removed. Unlike fluorescence, in which the absorbed energy is spontaneously emitted about 10^-8 second after excitation, phosphorescence requires additional excitation to produce radiation and may last from about mili second to days or years, depending on the circumstances.

phosphorus    →   fosfor

Phosphorus was discovered by Hennig Brandt (Germany) in 1669. The origin of the name comes from the Greek word phosphoros meaning bringer of light. White phosphorus is white to yellow soft, waxy phosphorescent solid with acrid fumes. Toxic by inhalation, ingestion, or skin contact. Red phosphorus is powdery, non-flammable and non-toxic. Phosphorus is found most often in phosphate rock. Pure form is obtained by heating a mixture of phosphate rock, coke and silica to about 1450 °C. Used in the production of fertilizers and detergents. Some is used in fireworks, safety matches and incendiary weapons. Phosphorus is also important in the production of steels, phosphor bronze and many other products.

photochemical reaction    →   fotokemijska reakcija

Photochemical reactions are those reactions which are conducted under the influence of light that is under the influence of ultraviolet, visible and infrared part of the light spectrum. Some systems can be influenced only by radiation that is absorbed by that system. Photochemical reactions are for example photosynthesis, creation of photography, generation of phosgene, creation of hydrochloride etc.

photoelectric effect    →   fotoelektrični efekt

Photoelectric effect is the complete absorption of a photon by a solid with the emission of an electron. The energy of a photon (hν) is

photomultiplier    →   fotomultiplikator

Photomultiplier (photomultiplier tube or PMT) is a very versatile and sensitive detector of radiant energy in the ultraviolet, visible, and near infrared regions of the electromagnetic spectrum. A typical photomultiplier tube consists of a photoemissive cathode (photocathode) followed by focusing electrodes, an electron multiplier (dynode) and an electron collector (anode) in a vacuum tube.

pickling    →   dekapiranje

Pickling is a process to chemically remove scale or oxide from steel to obtain a clean surface. When applied to bars or coils prior to bright drawing, the steel is immersed in a bath of dilute sulphuric acid (w(H₂SO₄) = 10 %) heated to a temperature of around 80 °C. An inhibitor is added to prevent attack and pitting of the cleaned metal. After pickling, a washing process takes place followed by immersion in a lime-water bath to neutralise any remaining acid.

picnometer    →   piknometar

Picnometer is a special glass flask which is used for determining a relative density of liquids using the weight of a known volume. It usually has a glass faceted cork which is pierced in the centre like a thin capillary through which surplus of liquid runs out.

piezoelectric effect    →   piezoelektrični efekt

Piezoelectric effect is voltage produced between surfaces of a solid dielectric (nonconducting substance) when a mechanical stress is applied to it. A small current may be produced as well. The effect, discovered by the French physicist Pierre Curie (1859-1906) in 1883, is exhibited by certain crystals, e.g., quartz and Rochelle salt, and ceramic materials. When a voltage is applied across certain surfaces of a solid that exhibits the piezoelectric effect, the solid undergoes a mechanical distortion. Piezoelectric materials are used in transducers, e.g., phonograph cartridges, microphones, and strain gauges, which produce an electrical output from a mechanical input, and in earphones and ultrasonic radiators, which produce a mechanical output from an electrical input.

pipette    →   pipeta

Pipettes are glass tubes which are tapers towards at both ends into narrow opened tubes. According to their design two types of pipettes can be distinguished:

Volumetric pipettes

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

Graduated pipettes

Graduated pipettes (Mohr pipette) have a scale divided into units of one and of 1/10th of a millilitre. Because of their wide necks it is less accurate than the volumetric pipette. They are used when taking volume of solutions in which accuracy does not have to be very high. They are filled in the same way as volumetric ones and liquid can be gradually released.

planary structure    →   planarna struktura molekule

Planary structure of molecule is a structure of molecule in which all atoms in the molecule lie in the same plane.