CHEMISTRY GLOSSARY

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.

polar molecule    →   polarna molekula

Polar molecules are molecules at which centres of gravity of positive and negative charge are not in the same point.

polarimeter    →   polarimetar

Polarimeter is an appliance which measures the angle of turning of polarisation light.

polarimetry    →   polarimetrija

Polarimetry measures the overall turning of the flat of polarised light. It is used when analysing optically active substances and compounds.

polarogram    →   polarogram

Polarogram is a graph of current versus potential in a polarographic analysis. The position of a polarographic wave in a polarogram along the x axis (E_1/2) provides an identity of the substance while the magnitude of the limiting diffusion current (i_d) provides the concentration of this substance.

polarography    →   polarografija

Polarography is a volumetric technique which is based on a diffusion controlled analyte travel to the surface of dropping mercury electrode (DME). The surface of the working electrode (dropping mercury electrode) is constantly renewed under dropping conditions and, thus, the conditions under which reaction takes place are readily reproducible. Depolarisation potential enables identification of ions present in the solution, and by measuring the diffusion current their concentration is calculated. Polarography was discovered in 1922 by the Czech chemist Jaroslav Heyrovský (1890-1967).

polychlorinated biphenyls    →   poliklorirani bifenili

Polychlorinated biphenyls (PCB) are poisonous and carcinogenic compounds. They are pollutants of both live and inanimate environment, and they are used as insulation and refrigerating materials in transformers and condensers.

polydentant ligand    →   polidentantni liganad

Polydentant ligands contain more co-ordination points (can give more electron pairs) and they form complex ringlike structures (celate complexes) by replacing two or more monodentant ligands. That kind of ligand is EDTA which has 6 co-ordinational points and with metals it creates complexes, always in 1:1 ratio.

polyester    →   poliester

Polyesters are copolymers formed by condensation polymerization of dicarboxylic acid (terephthalic acid) and a dialcohol, also called a diol (ethylene glycol).