CHEMISTRY GLOSSARY

pickling    →   dekapiranje

Pickling is a process to chemically remove scale or oxide from steel to obtain a clean surface. When applied to bars or coils prior to bright drawing, the steel is immersed in a bath of dilute sulphuric acid (w(H₂SO₄) = 10 %) heated to a temperature of around 80 °C. An inhibitor is added to prevent attack and pitting of the cleaned metal. After pickling, a washing process takes place followed by immersion in a lime-water bath to neutralise any remaining acid.

practical salinity    →   praktični salinitet

Practical salinity S_P is defined on the Practical Salinity Scale of 1978 (PSS-78) in terms of the conductivity ratio K₁₅ which is the electrical conductivity of the sample at temperature t₆₈ = 15 °C and pressure equal to one standard atmosphere, divided by the conductivity of a standard potassium chloride (KCl) solution at the same temperature and pressure. The mass fraction of KCl in the standard solution is 0.0324356 (32.4356 g of KCl in 1 kg of solution). When K₁₅ = 1, the Practical Salinity P S is by definition 35. The conductivity of that reference solution is C(35,1568,0) = 42.914 mS/cm = 4.2914 S/m (Siemens per meter). Note that Practical Salinity is a unit-less quantity. Though sometimes convenient, it is technically incorrect to quote Practical Salinity in "psu". When K₁₅ is not unity, S_P and K₁₅ are related by the PSS-78 equation

At a temperature of t₆₈ = 15 °C, R_t is simply K₁₅ and Practical Salinity S_P can be determined from the above equation. For temperatures other than t₆₈ = 15 °C, Practical Salinity S_P is given by the following function of R_t (k = 0.0162)

refractometer    →   refraktometar

Refractometer is an optical device used from measurement of refractive index. A refractometer takes advantage of the fact that light bends as it passes through different materials. It can be used to measure the salinity of water or the amount of sugar in fresh grapes. Refractometers are available with or without automatic temperature compensation (ATC).

When using a conventional saltwater refractometer, a sample is placed on an optical prism in the sample window. As light shines through the sample, it is bent according to the salinity of the water, and casts a shadow on the scale that is visible through the eyepiece. Salinity is read directly through the eyepiece.

salinity    →   salinitet

Salinity (S) is a measure of the quantity of dissolved salts in seawater. It is formally defined as the total amount of dissolved solids in seawater in parts per thousand (‰) by weight when all the carbonate has been converted to oxide, the bromide and iodide to chloride, and all organic matter is completely oxidized.

Chlorinity is the oldest of the salinity measures considered and is still a corner-stone in the study of dissolved material in seawater. Based on the principle of constant relative proportions it provides a measure of the total amount of dissolved material in seawater in terms of the concentration of halides. The relationship between chlorinity (Cl) and salinity as set forth in Knudsen’s tables is

In 1962, however, a better expression for the relationship between total dissolved salts and chlorinity was found to be

Practical Salinity (S_P) was introduced as a replacement for Chlorinity. Practical Salinity is is relatively easy to measure using standard conductometers, measurements are more precise and less time consuming than measurements of Chlorinity and accurate measurements can even be made in situ. Practical salinity S_P is defined on the Practical Salinity Scale of 1978 (PSS-78) in terms of the conductivity ratio K₁₅ which is the electrical conductivity of the sample at temperature t₆₈ = 15 °C and pressure equal to one standard atmosphere, divided by the conductivity of a standard potassium chloride (KCl) solution at the same temperature and pressure. The mass fraction of KCl in the standard solution is 0.0324356 (32.4356 g of KCl in 1 kg of solution).

Note that Practical Salinity is a unit-less quantity. Though sometimes convenient, it is technically incorrect to quote Practical Salinity in "psu". For most purposes one can assume that the psu and the ‰, are synonymous.

The global average salinity of ocean waters is about 35 ‰, that is, about 35 g of solid substances are dissolved in 1 kg of seawater.

T-S diagram    →   T-S dijagram

The relationship between the temperature (T) and the salinity (S) of a seawater can be illustrated graphically on a T-S diagram, which is a simple, but powerful tool used in studies of seawater density, mixing, and circulation. In a T-S diagram, temperature is plotted along the vertical axis in degrees Celsius and salinity is measured along the horizontal axis in PSU (Practical Salinity Units). Seawater density is illustrated in the diagram by curved lines of constant density (isopycnals). Water tends to move horizontally throughout the deep ocean, moving along lines of equal density.

absolute zero    →   apsolutna nula temperature

Absolute zero is theoretically, the lowest attainable temperature. It is the energy at which the kinetic energy of atom and molecules is minimal and is equivalent to -273.15 °C.

Acheson process    →   Achesonov proces

Acheson process is an industrial process to synthesize graphite and silicon carbide (carborundum), named after its inventor the American chemist Edward Goodrich Acheson (1856-1931). In this process, a solid-state reaction between pure silica sand (SiO₂) and petroleum coke (C) at very high temperature (more than 2500 °C) leads to the formation of silicon carbide under the general reaction:

While studying the effects of high temperature on carborundum, Acheson had found that silicon vaporizes at about 4150 °C, leaving behind graphitic carbon.

activation energy    →   energija aktivacije

Activation energy (E_a) is the energy that must be added to a system in order for a process to occur, even though the process may already be thermodynamically possible. In chemical kinetics, the activation energy is the height of the potential barrier separating the products and reactants. It determines the temperature dependence on the reaction rate.

adiabatic process    →   adijabatski proces

Adiabatic process is a thermodynamic process in which no heat enters or leaves the system. In general, an adiabatic change involves a fall or rise in temperature of the system.

allotrope    →   alotrop

Allotropes are the elements which exist in two or more different forms in the same physical state. Allotropes generally differ in physical properties and may also differ in chemical activity.

Diamond, graphite and fullerenes are three allotropes of the element carbon. Graphite is a soft, black, slippery substance; by contrast, diamond is one of the hardest substances known. The different properties of the allotropes arise from their chemical structures. Diamonds typically crystallize in the cubic crystal system and consist of tetrahedrally bonded carbon atoms. Graphite crystallizes in the hexagonal system. In the fullerenes, the carbon atoms taking the form of a hollow sphere, ellipsoid, or tube.

In some cases, the allotropes are stable over a temperature range, with a definite transition point at which one changes into the other. For instance, tin has two allotropes: white (metallic) tin stable above 13.2 °C and grey (nonmetallic) tin stable below 13.2 °C.

The term allotropes may also be used to refer to the molecular forms of an element. Ozone is a chemically active triatomic allotrope of the element oxygen.