CHEMISTRY GLOSSARY

Bohr magneton    →   Bohrov magneton

Bohr magneton (μ_B) is the atomic unit of magnetic moment, defined as

where h is Planck’s constant, m_e the electron mass, and e the elementary charge. It is the moment associated with a single electron spin.

cellulose    →   celuloza

Cellulose, (C₆H₁₀O₅)_n, is a polysaccharide that consists of a long unbranched chain of glucose units linked by (1→4)-β-glycoside bonds. Nature uses cellulose primarily as a structural material to impart strength and rigidity to plants. Leaves, grasses, and cotton are primarily cellulose. The fibrous nature of extracted cellulose has led to its use in textile industry for the production of cotton, artificial silk, etc. Cellulose also serves as raw material for the manufacture of cellulose acetate, known commercially as acetate rayon, and cellulose nitrate, known as guncotton. Gunncotton is the major ingredient in smokeless powder, the explosive propellant used in artillery shells and in ammunition for firearms.

centrifuge    →   centrifuga

Centrifuge is a device in which solid or liquid particles of different densities are separated by rotating them in a tube in a horizontal circle. The dense particles tend to move along the length of the tube to a greater radius of rotation, displacing the lighter particles to the other end.

chiral molecule    →   kiralne molekule

Chiral molecule is a molecule which cannot be superimposed on its mirror image. A common example is an organic molecule containing a carbon atom to which four different atoms or groups are attached. Such molecules exhibit optical activity, i.e., they rotate the plane of a polarised light beam.

nucleon    →   nukleon

Nucleon is a collective term for the proton and neutron.

nuclide    →   nuklid

Nuclide is a species of atoms in which each atom has identical atomic number Z and identical mass number A. For example, a carbon-14 (C-14 or ¹⁴C) nuclide is the nucleus of a carbon atom, which has six protons and eight neutrons.

osmometry    →   osmometrija

Osmometry is a determination of the average molecular weight of a dissolved substance from measurements of osmotic pressure.

chlorinity    →   klorinitet

Originally chlorinity (symbol Cl) was defined as the weight of chlorine in grams per kilogram of seawater after the bromides and iodides had been replaced by chlorides. To make the definition independent of atomic weights, chlorinity is now defined as 0.3285233 times the weight of silver equivalent to all the halides.

The Mohr-Knudsen titration method served oceanographers for more than 60 years to determine salinity from chlorinity. This modification of the Mohr method uses special volumetric glassware calibrated directly in chlorinity units. The Mohr method uses potassium chromate (K₂CrO₄) as an indicator in the titration of chloride ions chloride (plus a small amount of bromide and iodide) with a silver nitrate (AgNO₃) standard solution.

The other halides present are similarly precipitated.

A problem in the Mohr titration was that silver nitrate is not well suited for a primary standard. The Danish physicist Martin Knudsen (1871-1949) suggested that a standard seawater (Eau de mer Normale or Copenhagen Normal Water) be created and distributed to oceanographic laboratories throughout the world. This water was then used to standardize the silver nitrate solutions. In this way all chlorinity determinations were referred to one and the same standard which gave great internal consistency.

The relationship between chlorinity Cl and salinity S 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

radioactivity    →   radioaktivnost

Radioactivity is capability of a spontaneous decay of an atom. In this way a new atom type is formed and radioactive radiation is released. An atom can emit three types of radioactive radiation: positive α-radiation, negative β-radiation and electrically neutral γ-radiation. During radioactive decay one element never emits all types of radiation at the same time.

sand filtration    →   pješčana filtracija

Sand filtration is a frequently used and very robust method of removing suspended solids from water. The filtration medium consists of a multiple layer of sand with a variety in size and specific gravity. Sand filters can be supplied in different sizes and materials, both hand operated and fully automatically.