CHEMISTRY GLOSSARY

sugar    →   šećer

Sugar is any of a group of water-soluble carbohydrates of relatively low molecular weight and typically having a sweet taste. The group comprises mainly monosaccharides (glucose, fructose, galactose), disaccharides (sucrose, lactose, maltose), and trisaccharides (raffinose). Many monosaccharides and disaccharides fairly commonly found in nature bear names reflecting the source from which they were first isolated. For example, glucose is also known as grape sugar, lactose as milk sugar, and maltose as malt sugar. In everyday usage, the name is often used to refer specifically to sucrose (table sugar, cane sugar, beet sugar).

superfluid helium    →   superfluidni helij

Superfluidity in helium-4 was discovered in 1938 by the Soviet physicist Pyotr Leonidovich Kapitsa. Helium-4 exhibits superfluidity when it is cooled below 2.18 K (-270.97 C), which is called the lambda (λ) point. At these temperatures, helium-4 exhibits the characteristics of two distinct fluids, one of which appears to flow without friction. An extensive series of experiments showed that in this state of helium, called helium II (He II), there is an apparent enormous rise in heat conductivity, at an increase rate of about three million. Another unusual property of He II is its mobile, rapid flow through capillaries or over the rim of its containment vessel as a thin film that exhibits no measurable viscosity and appears unaffected by the forces of gravity or evaporation and condensation.

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.

tellurium    →   telurij

Tellurium was discovered by Franz Joseph Muller von Reichstein (Romania) in 1782. The origin of the name comes from the Latin word tellus meaning earth. It is silvery-white, brittle semi-metal. Unreactive with water or HCl; dissolves in HNO₃; burns in air or oxygen. Tellurium is obtained as a by-product of copper and lead refining. Used to improve the machining quality of copper and stainless steel products and to colour glass and ceramics. Also in thermoelectric devices. Some is used in the rubber industry and it is a basic ingredient in manufacturing blasting caps.

three way safety bulb    →   propipeta

Three way safety bulb (pipette filler bulb) is used for pipeting. The attachment is placed over the mouth of the pipet. Squeeze the air valve (A) and the bulb simultaneously to empty the bulb of air. Place the tip of the pipet below the solution's surface in the beaker. Gradually squeeze the suction valve (S) to draw liquid into the pipet. If the level of the solution is not high enough, squeeze the air valve (A) and the bulb again to expel the air from the bulb. Draw up more liquid by squeezing the suction valve (S). When the liquid is above the specified volume, stop squeezing the suction valve (S). Do not remove the bulb from the pipet. Do not allow liquid to enter the pipet bulb.

titration curve    →   titracijska krivulja

Titration curve is a graphic representation of the amount of a species present vs. volume of solution added during a titration. A titration curve has a characteristic sigmoid curve. The inflection point in the titration curve marks the end-point of the titration. Blue line is the first derivative of the titration curve.

transition metal    →   prijelazni element

This group of metals is distinguished from other metals not by their physical properties, but by their electronic structure. Transition metals are elements characterized by a partially filled d subshell. The First Transition Series comprises scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu). The Second and Third Transition Series include the lanthanides and actinides, respectively.

The transition metals are noted for their variability in oxidation state. Thus, manganese has two electrons in its outside shell and five electrons in the next shell down, and exhibits oxidation states of +1, +2, +3, +4, +5, +6, and +7.

They are also characterised by the fact that well into the series, going from left to right, the properties of the succeeding metals do not differ greatly from the preceding ones.

Winkler’s method    →   Winklerova metoda

Winkler’s method was once a common method used to determine the dissolved oxygen concentration by titration. Now rarely used due to the accuracy and low price of oxygen meters.

The water sample is first treated with excess manganese(II) sulfate solution and then with an alkaline solution of potassium iodide. The Mn(OH)₂ initially formed reacts with the dissolved oxygen. The amount of MnO(OH)₂ formed is determined by reaction with iodide ion in acidic solution. The iodine formed may be titrated against standard thiosulfate solution, using starch as an indicator.

X-ray diffraction    →   rendgenska difrakcija

The regular array of atoms in a crystal is a three-dimensional diffraction grating for short-wavelength waves such as X-rays. The atoms are arranged in planes with interplanar spacing d. Diffraction maxima occur in the incident direction of the wave, measured from the surface of a plane of atoms, and the wavelength λ of the radiation satisfy Braggs’s law:

Ziegler process    →   Zieglerov proces

Ziegler process is an industrial process for the manufacture of high-density polyethene using catalysts of titanium(IV) chloride (TiCl₄) and aluminium alkyls (e.g. triethylaluminium, Al(C₂H₅)₃). The process was introduced in 1953 by the German chemist Karl Ziegler (1898-1973). It allowed the manufacture of polythene at lower temperatures (about 60 °C) and pressures (about 1 atm) than used in the original process.