CHEMISTRY GLOSSARY

distilled water    →   destilirana voda

Distilled water is water purified by distillation so as to free it from dissolved salts and other compounds. Distilled water in equilibrium with the carbon dioxide in the air has conductivity of about 0.8×10^-6 S cm^-1. Repeated distillation in vacuum can bring conductivity down to 0.043×10^-6 S cm^-1 at 18 °C. The limiting conductivity is due to self ionisation

pK    →   pK

pK is the negative logarithm (base 10) of an equilibrium constant K.

vapour pressure    →   tlak pare

Vapour pressure is the pressure of a gas in equilibrium with a liquid (or, in some usage, a solid) at a specified temperature.

vibration    →   vibracije

Vibration are small deflections of a body around equilibrium point, which usually can be described by simple harmonic motion.

weak electrolyte    →   slabi elektrolit

Weak electrolytes are those electrolytes which in water solutions dissociate only partially, giving ions and which are in equilibrium with undissociated molecules. Their water solutions conduct electric current weakly. For example, acetic acid partially dissociates into acetate ions and hydrogen ions, so that an acetic acid solution contains both molecules and ions.

electrode of the first kind    →   elektroda prvog reda

Electrode of the first kind is a simple metal electrode immersed in a solution containing its own ion (e.g., silver immersed in a silver nitrate solution). The equilibrium potential of this electrode is a function of the concentration (more correctly of activity) of the cation of the electrode metal in the solution (see Nernst’s electrode potential equation).

electrode of the second kind    →   elektroda drugog reda

Electrodes of the second kind are metal electrodes assembly with the equilibrium potential being a function of the concentration of an anion in the solution. Typical examples are the silver/silver-chloride electrode and the calomel electrode. The potential of the metal is controlled by the concentration of its cation in the solution, but this, in turn, is controlled by the anion concentration in the solution through the solubility product of the slightly soluble metal salt. Contrast with electrode of the first kind and electrode of the third kind.

electrode of the third kind    →   elektroda trećeg reda

Electrode of the third kind is a metal electrode assembly with the equilibrium potential being a function of the concentration of a cation, other than the cation of the electrode metal, in the solution. The assembly consists of a metal in contact with two slightly soluble salts (one containing the cation of the solid metal, the other the cation to be determined, with both salts having a common anion) immersed in a solution containing a salt of the second metal (e.g., zinc metal--zinc oxalate--calcium oxalate--calcium salt solution). The potential of the metal is controlled by the concentration of its cation in the solution, but this is controlled by the anion concentration in the solution through the solubility product of the slightly soluble metal salt, which, in turn is controlled by the concentration of the cation of the second slightly soluble salt. These electrodes are very sluggish and unstable due to a series of equilibria to be established to produce a stable potential.

equal-arm balance    →   vaga s jednakim krakovima

The simplest type of balance, the equal-arm balance, is an application of a first class lever. The beam of the balance is supported on a central knife-edge, usually of agate, which rests upon a plane agate plate. The point of support is called the fulcrum. Two pans of equal weight are suspended from the beam, one at each end, at points equidistant from the fulcrum. A long pointer attached at right angles to the beam at the fulcrum indicates zero on a scale when the beam is at rest parallel to a level surface.

To prevent the knife-edge from becoming dull under the weight of the beam and pans the balance is equipped with a special device called an arrest. The arrest is operated by means of milled knob underneath the base plate in the middle and in front of the balance (sometimes the arrest knob is at one side of the balance).

The object to be weighed is placed on one pan, and standard weights are added to the other until the balance of the beam is established again. When not in use and during loading or unloading of the pans, the balance should be arrested.

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.