CHEMISTRY GLOSSARY

mass-energy equivalence    →   ekvivalencija mase i energije

In the special theory of relativity Einstein demonstrated that neither mass nor energy were conserved separately, but that they could be traded one for the other and only the total "mass-energy" was conserved. The relationship between the mass and the energy is contained in what is probably the most famous equation in science,

Where m is the mass of the object and c is the velocity of light. Cockcroft and Walton (1932) are routinely credited with the first experimental verification of mass-energy equivalence.

molar mass    →   molarna masa

Molar mass is the mass of one mole of a substance.

It is normally expressed in units of g mol^-1, in which case its numerical value is identical with the relative molecular mass.

picnometer    →   piknometar

Picnometer is a special glass flask which is used for determining a relative density of liquids using the weight of a known volume. It usually has a glass faceted cork which is pierced in the centre like a thin capillary through which surplus of liquid runs out.

polymer    →   polimer

Polymer is a substance composed of molecules of high relative molecular mass (molecular weight), the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass (monomers). In most cases the number of monomers is quite large and is often not precisely known. A single molecule of a polymer is called a macromolecule. Polystyrene is light solid material obtained by polymerisation of styrene (vinyl benzene).

potassium    →   kalij

Potassium was discovered by Sir Humphry Davy (England) in 1807. The origin of the name comes from the Arabic word qali meaning alkali (the origin of the symbol K comes from the Latin word kalium). It is soft, waxy, silver-white metal. Fresh surface has silvery sheen. Quickly forms dull oxide coating on exposure to air. Reacts strongly with water. Reacts with water to give off flammable gas. Reacts violently with oxidants. Occurs only in compounds. Potassium is found in minerals like carnallite [(KMgCl₃)·6H₂O] and sylvite (KCL). Pure metal is produced by the reaction of hot potassium chloride and sodium vapours in a special retort. Used as potash in making glass and soap. Also as saltpetre, potassium nitrate (KNO₃) to make explosives and to colour fireworks in mauve. Vital to function of nerve and muscle tissues.

ribonucleic acid    →   ribonukleinska kiselina

Ribonucleic acid is a complex organic compound in living cells that is concerned with protein synthesis. Plays an intermediary role in converting the information contained in DNA into proteins. RNA carries the genetic information from DNA to those parts of the cell where proteins are made. Some viruses store their genetic information as RNA not as DNA.

Ribonucleic acid is a similar molecule to DNA but with a slightly different structure.

The structural difference with DNA is that RNA contains a -OH group both at the 2' and 3' position of the ribose ring, whereas DNA (which stands, in fact, for deoxy-RNA) lacks such a hydroxy group at the 2' position of the ribose. The same bases can be attached to the ribose group in RNA as occur in DNA, with the exception that in RNA thymine does not occur, and is replaced by uracil, which has an H-group instead of a methyl group at the C-5 position of the pyrimidine. Unlike the double-stranded DNA molecule, RNA is a single-stranded molecule.

The three main functionally distinct varieties of RNA molecules are: (1) messenger RNA (mRNA) which is involved in the transmission of DNA information, (2) ribosomal RNa (rRNA) which makes up the physical machinery of the synthetic process, and (3) transfer RNA (tRNA) which also constitutes another functional part of the machinery of protein synthesis.

salt water    →   slana voda

Salt water is the water of the sea and the ocean. This water contains a relatively high percentage of dissolved salt (about 35 g of salt per 1 000 g of sea water.). About 90 % of that salt would be sodium chloride, or ordinary table salt.

The salinity of ocean water varies. It is affected by such factors as melting of ice, inflow of river water, evaporation, rain, etc.

significant figures    →   značajne znamenke

Measurements are not infinitely accurate: we must estimate measurement uncertainty. The number of significant figures is all of the certain digits plus the first uncertain digit.

Rules for significant figures:

1. Disregard all initial zeros.
2. Disregard all final zeros unless they follow a decimal point.
3. All remaining digits including zeros between nonzero digits are significant.

In addition and subtraction, the number of significant figures in the answer depends on the original number in the calculation that has the fewest digits to the right of the decimal point.

In multiplication and division, the number of significant figures in a calculated result is determined by the original measurement that has the fewest number of significant digits.

In a logarithm of a number, keep as many digits to the right of the decimal point as there are significant figures in the original number.

In an antilogarithm of a number, keep as many digits as there are digits to the right of the decimal point in the original number.

standard electrode potential    →   standardni elektrodni potencijal

Standard electrode potential (E°) (standard reduction potentials) are defined by measuring the potential relative to a standard hydrogen electrode using 1 mol solution at 25 °C. The convention is to designate the cell so that the oxidised form is written first. For example,

The e.m.f. of this cell is -0.76 V and the standard electrode potential of the Zn²+|Zn half cell is -0.76 V.

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).