CHEMISTRY GLOSSARY

optical activity    →   optička aktivnost

Optical activity is the ability of a chiral molecule to rotate the plane of plane-polairzed light. Molecules of an optically active substance cannot be superimposed on their own mirror images, just as your left hand cannot be superimposed on your right when both are held palm-down.

orbital    →   orbitala

Orbital is the area in space about an atom or molecule in which the probability of finding an electron is greatest.

The possible atomic orbitals correspond to subshells of the atom. Thus there is one s-orbital for each shell (orbital quantum number l = 0). There are three p-orbitals (corresponding to the three values of l) and five d-orbitals. The shapes of orbitals depend on the value of l.

transmittance    →   transmitancija

Transmittance (τ) is the ratio of the radiant or luminous flux at a given wavelength that is transmitted to that of the incident radiation. Also called transmission factor.

ultracentrifuge    →   ultracentrifuga

Ultracentrifuge is a high-speed centrifuge used in the separation of colloidal or submicroscopic particles. The ultracentrifuge can generate forces thousands or millions of times stronger than the force of gravity.

urethane    →   uretan

Urethane is actually a misnomer as applied to polyurethane foam. It is a colorless, crystalline substance used primarily in medicines, pesticides, and fungicides. Urethane is not used in the production of urethane polymers or foams. The urethanes of the plastics industry are so named because the repeating units of their structures resemble the chemical urethane.

osmotic pressure    →   osmotski tlak

Osmotic pressure (Π) is the excess pressure necessary to maintain osmotic equilibrium between a solution and a pure solvent separated by a membrane permeable only to the solvent. In an ideal dilute solution

where c_B is the amount-of-substance concentration of the solute, R is the molar gas constant, and T the temperature.

Ostwald’s process    →   Ostwaldov proces

Ostwald’s process is a process by which the nitric acid can be obtained in three degrees. In the first stage ammonia and oxygen react (with platinum-rhodium as a catalyst), whereby the nitrogen monoxide and water emerge

In the second stage nitrogen monoxide reacts with oxygen whereby nitrogen dioxide emerges

and in the third stage nitrogen dioxide dissolves in water, in the presence of air, giving the nitric acid

Ostwald’s viscometer    →   Ostwaldov viskozimetar

Ostwald viscometer, also known as U-tube viscometer or capillary viscometer is a device used to measure the viscosity of the liquid with a known density. The method of determining viscosity with this instrument consists of measuring the time for a known volume of the liquid (the volume contained between the marks A and B) to flow through the capillary under the influence of gravity. Ostwald viscometers named after the German chemist Wilhelm Ostwald (1853-1932).

The instrument must first be calibrated with materials of known viscosity such as pure (deionized) water. Knowing the value of viscosity of one liquid, one can calculate the viscosity of other liquid.

where η₁ and η₂ are viscosity coefficients of the liquid and water, and ρ₁ and ρ₂ are the densities of liquid and water, respectively.

vacuum distillation    →   vakuum destilacija

Vacuum distillation is distillation under reduced pressure. The depression in the boiling point of the substance distilled means that the temperature is lower, which may prevent the substance from decomposing.

van der Waals’s radius    →   van der Waalsov radijus

Van der Waals’s radius is one half the distances between two nonbonded atoms, when attractive and repulsive forces between the atoms are balanced.