CHEMISTRY GLOSSARY

Tyndall’s effect    →   Tyndallov efekt

Tyndall’s effect occurs when light disperses on colloid particles. This phenomenon can be seen when a ray of light enters in dark room through a small hole. In the beam some dust particles of colloid dimensions can be seen sparkling.

valence bond theory    →   teorija valentne veze

Valence bond theory is a theory that explains the shapes of molecules in terms of overlaps between half-filled atomic orbitals, or half filled hybridised orbitals.

zero law of thermodynamics    →   nulti zakon termodinamike

Zero law of thermodynamics states: If some body A is in thermal equilibrium with body B and with body C, then bodies B and C are also in thermal equilibrium.

periodic table of the elements    →   periodni sustav elemenata

Periodic table is a table of elements, written in sequence in the order of atomic number or atomic weight and arranged in horizontal rows (periods) and vertical columns (groups) to illustrate the occurrence of similarities in the properties of the elements as a periodic function of the sequence. The original form was proposed by Dmitri Mendeleev (1834-1907) in 1869, using relative atomic masses.

potentiometric titration    →   potenciometrijska titracija

Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume. Types of potentiometric titrations for the determination of analytes in photoprocessing solutions include acid-base, redox, precipitation, and complexometric.

Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.

A titration curve has a characteristic sigmoid curve. The part of the curve that has the maximum change marks the equivalence point of the titration. The first derivative, ΔE/ΔV, is the slope of the curve, and the endpoint occurs at the volume, V', where ΔE/ΔV has the maximum value.

redox titration    →   redoks-titracija

Redox titration (oxidation-reduction titration) is a titration based on a redox reaction. For example, iron in water can be determined by converting dissolved iron to Fe²⁺ and titrating the solution with potassium permanganate (KMnO₄), a powerful oxidising agent.

salt fog test    →   ispitivanje u slanoj komori

Salt fog test is an accelerated corrosion test in which specimens are exposed to a fine mist of a solution usually containing sodium chloride (typically 5 %). Other contaminants can be added according to desired conditions. It is mainly used to determine the effectiveness of material finishes and protective coatings on materials. Salt-fog testing is also used to determine the effects of salt deposits on the electrical functions of electronic assemblies.

simple tetragonal lattice    →   jednostavna tetragonska rešetka

Simple or primitive tetragonal lattice (tetragonal-P) has one lattice point at the each corner of the unit cell. It has unit cell vectors a=b≠c and interaxial angles α=β=γ=90°.

Tafel plot    →   Tafelov dijagram

Tafel plot is the graph of the logarithm of the current density j against the overpotential η in electrochemistry in the high overpotential limit. An electrode when polarised frequently yields a current potential relationship over a region which can be approximated by:

where η is change in open circuit potential, i is the current density, B and i₀ is constants. B is known as the Tafel Slope. If this behaviour is observed a plot of the semilogarithmic components is known as the Tafel line and the diagram is called the Tafel diagram.

tantalum    →   tantal

Tantalum was discovered by Anders Ekeberg (Sweden) in 1802. The origin of the name comes from the Greek word Tantalos meaning father of Niobe in Greek mythology, (tantalum is closely related to niobium in the periodic table). It is rare, grey, heavy, hard but ductile, metal with a high melting point. Exposed surfaces form corrosion resistant oxide film. Attacked by HF and fused alkalis. Metal ignites in air. Tantalum always found with niobium. Chiefly occurs in the mineral tantalite. Often used as an economical substitute for platinum. Tantalum pentoxide is used in capacitors and in camera lenses to increase refracting power. It and its alloys are corrosion and wear resistant so it is used to make surgical and dental tools.