CHEMISTRY GLOSSARY

ash    →   pepeo

Ash is an inorganic part of some matter or mixture which remains after the organic part has burnt up.

atmospheric pressure    →   atmosferski tlak

Atmospheric pressure is the pressure exerted by weight of the air above it at any point on the earth’s surface. At sea level the atmosphere will support a column of mercury about 760 mm high. This decreases with increasing altitude. The standard value for the atmospheric pressure at sea level in SI units is 101 325 Pa.

atomic clock    →   atomski sat

Atomic clock is an apparatus for standardizing time based on periodic phenomena within atoms or molecules (ammonia clock; caesium clock).

analytical balance    →   analitička vaga

Analytical balances are instruments used for precise determining mass of matter. Analytical balances are sensitive and expensive instruments, and upon their accuracy and precision the accuracy of analysis result depends. The most widely used type of analytical balances are balances with a capacity of 100 g and a sensitivity of 0.1 mg. Not one quantitative chemical analysis is possible without usage of balances, because, regardless of which analytical method is being used, there is always a need for weighing a sample for analysis and the necessary quantity of reagents for solution preparation.

The working part of the balance is enclosed in a glass-fitted case. The baseplate is usually of black glass or black slate. The beam has agate knife-edges at its extremes, supporting stirrups from which balance pans are suspended. Another agate or steel knife-edge is fixed exactly in the middle of the beam on its bottom side. This knife-edge faces downwards and supports the beam. When not in use and during loading or unloading of the pans, the balance should be arrested.

The principle of operation of a modern laboratory balance bears some resemblance to its predecessor - the equal arm balance. The older instrument opposed the torque exerted by an unknown mass on one side of a pivot to that of an adjustable known weight on the other side. When the pointer returned to the center position, the torques must be equal, and the weight was determined by the position of the moving weights.

Modern electronic laboratory balances work on the principle of magnetic force restoration. In this system, the force exerted by the object being weighed is lifted by an electromagnet. A detector measures the current required to oppose the downward motion of the weight in the magnetic field.

angular acceleration    →   kutna akceleracija

If the angular velocity of a body changes from an initial value ω_i to a final value ω_f, average angular acceleration, α, can be defined for the time interval Δt = t_f - t_i:

The instantaneous angular acceleration, α, is the limit of the average angular acceleration, as Δt is made to approach zero:

SI unit for angular acceleration is s^-2.

angular velocity    →   kutna brzina

A point-like object that undergoes circular motion changes its angular position from initial Θ_i to final Θ_f, relative to a fixed axis, specified in a coordinate system with an origin that coincides the centre of the circular path of object. The change in its angular position is called angular displacement ΔΘ = Θ_f - Θ_i. Also, a rigid body that rotates about a specified rotation axis, changing its angular position from initial Θ_i to final Θ_f, undergoes an angular displacement ΔΘ.

The average angular velocity, ω_av, is the ratio of the angular displacement and the time interval Δt=t_f-t_i, in which that displacement occurs.

Θ_f and Θ_i are the initial and final angular position, respectively.

The instantaneous angular velocity ω is the limit of the average angular velocity, as Δt is made to approach zero.

ω_av and ω are positive for the counterclockwise rotation (in direction of increasing Θ) and negative for the clockwise rotation (in direction of decreasing Θ).

SI unit for angular velocity is s^-1.The measure for the angle Θ is radian. The relationship between radians and degrees is:

For example, the angular velocity of the minute hand of a clock is:

atomic spectroscopy    →   atomska spektroskopija

Atomic spectroscopy is an expensive analytical method which uses absorption (AAS), emission (AES) and fluorescent (AFS) characteristics of the analyte.

anhydrous    →   anhidrid

Anhydrous (without water) is an applied to minerals which do not contain water of crystallization or water of chemical combination. For example, strongly heated copper (II) sulphate pent hydrate (CuSO₄•5H₂O) produces anhydrous copper (II) sulphate (CuSO₄). Less stable and more dangerous to use than hydrated.

anomer    →   anomer

Anomers are diastereoisomers of cyclic forms of sugars or similar molecules differing in the configuration at the anomeric carbon (C-1 atom of an aldose or the C-2 atom of a 2-ketose). The cyclic forms of carbohydrates can exist in two forms, α- and β- based on the position of the substituent at the anomeric center. Anomer are designated α if the configuration at the anomeric carbon is the same as that at the reference asymmetric carbon in a Fischer projection. If the configuration differs the anomer is designated β. For example, α-D-glucopyranose and β-D-glucopyranose, the two cyclic forms of glucose, are anomers.

antimony    →   antimon

Antimony has been known since ancient times. The origin of the name comes from the Latin word stibium meaning mineral stibnite. It is hard, brittle, silvery-white semimetal. Stable in dry air. Toxic by ingestion or inhalation. Antimony is found in stibnite (Sb₂S₃) and in valentinite (Sb₂O₃). It is alloyed with other metals to increase their hardness. Also in the manufacture of a few special types of semiconductor devices. Also in plastics and chemicals. A few kinds of over-the-counter cold and flu remedies use antimony compounds.