CHEMISTRY GLOSSARY

graduated pipette    →   graduirana pipeta

Graduated pipettes (Mohr pipette) have a scale divided into units of one and of 1/10th of a millilitre. Because of their wide necks it is less accurate than the volumetric pipette. They are used when taking volume of solutions in which accuracy does not have to be very high. By sucking in (with mouth, propipette or a water pump) the liquid is pulled in a little bit above the mark and the opening of the pipet is closed with a forefingertip. Outer wall of pipet is wiped and, with a slight forefinger loosening, the liquid is released until it reaches the mark 0. A pipette is emptied out by lifting the forefinger off and letting the liquid flow out of the pipette freely.

ligand    →   ligand

Ligand is an ion (F^-, Cl^-, Br^-, I^-, S^2-, CN^-, NCS^-, OH^-, NH₂^-) or molecule (NH₃, H₂O, NO, CO) that donates a pair of electrons to a metal atom or ion in forming a coordination complex. The main way of classifying ligands is by the number of points at which they are attached to, or bound to, the metal center. This is the denticity. Ligands with one potential donor atom are monodentate. Polydentate ligand is a ligand that is attached to a central metal ion by bonds from two or more donor atoms. Ligands with more than one potential donor atom are known as ambidentate, such as the thiocyanate ion, NCS-, which can bind to the metal center with either the nitrogen or sulphur atoms. Chelating ligands are those polydentate ligands which can form a ring including the metal atom.

Gratzel solar cell    →   Gratzelova sunčeva ćelija

Grätzel solar cell is photoelectrochemical cell, developed by Michael Grätzel and collaborators, simulates some characteristics of the natural solar cell, which enables photosynthesis take place. In natural solar cell the chlorophyll molecules absorb light (most strongly in the red and blue parts of the spectrum, leaving the green light to be reflected). The absorbed energy is sufficient to knock an electron from the excited chlorophyll. In the further transport of electron, other molecules are involved, which take the electron away from chlorophyll. In Grätzel cell, the tasks of charge-carrier generation and transport are also assigned to different species.

His device consists of an array of nanometre-sized crystallites of the semiconductor titanium dioxide, welded together and coated with light-sensitive molecules that can transfer electrons to the semiconductor particles when they absorb photons. So, light-sensitive molecules play a role equivalent to chlorophyll in photosynthesis. In Grätzel cell, the light-sensitive molecule is a ruthenium ion bound to organic bipyridine molecules, which absorb light strongly in the visible range; titanium dioxide nanocrystals carry the received photoexcited electrons away from electron donors. On the other hand, a donor molecule must get back an electron, so that it can absorb another photon. So, this assembly is immersed in a liquid electrolyte containing molecular species (dissolved iodine molecules) that can pick up an electron from an electrode immersed in the solution and ferry it to the donor molecule. These cells can convert sunlight with efficiency of 10 % in direct sunlight and they are even more efficient in diffuse daylight.

macromolecule    →   makromolekule

Macromolecule is a molecule of high relative molecular mass (molecular weight), the structure of which essentially comprises the multiple repetitions of units derived, actually or conceptually, from molecules of low relative molecular mass. The types of macromolecules are natural and synthetic polymers, carbohydrates, lipids, proteins etc. Cellulose is a polysaccharide that is made up of hundreds, even thousands of glucose molecules strung together.

measuring cylinder    →   menzura

Measuring cylinders (graduated cylinders) are graduated glass cylinders with a capacity from 2 mL to 2 L. They are used when reagent solutions for volume measuring are prepared when accuracy is not of great relevance. The larger the measuring cylinder, the bigger the measuring error.

niobium    →   niobij

Niobium was discovered by Charles Hatchett (England) in 1801. The origin of the name comes from the Greek word Niobe meaning daughter of Tantalus in Greek mythology (tantalum is closely related to niobium in the periodic table). It is shiny white, soft, ductile metal. Exposed surfaces form oxide film. Niobium occurs in a mineral columbite. It is used in stainless steel alloys for nuclear reactors, jets and missiles. Used as an alloy with iron and nickel. It can be used in nuclear reactors and is known to be superconductive when alloyed with tin, aluminium or zirconium.

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.

pipette    →   pipeta

Pipettes are glass tubes which are tapers towards at both ends into narrow opened tubes. According to their design two types of pipettes can be distinguished:

Volumetric pipettes

Volumetric pipettes (transfer or belly pipette) are used in volumetric analysis, when there is a need for taking exact smaller volume of a sample solution or reagent. The upper tube of volumetric pipette has a ringlike marking (mark) which marks its calibrated volume. Pipettes calibrated to deliver (TD or Ex) the indicated volume. By sucking in (with mouth, propipette or a water pump) the liquid is pulled in a little bit above the mark and the opening of the pipet is closed with a forefingertip. Outer wall of pipet is wiped and, with a slight forefinger loosening, the liquid is released until it reaches the mark. Mark must figure as a tangent on a lower edge of the liquid meniscus. A pipette is emptied out by lifting the forefinger off and letting the liquid flow out of the pipette freely. After another 15 s and the tip of the pipette is pulled onto the inner wall of the vessel. It is absolutely forbidden to blow out the contents of the pipette

Graduated pipettes

Graduated pipettes (Mohr pipette) have a scale divided into units of one and of 1/10th of a millilitre. Because of their wide necks it is less accurate than the volumetric pipette. They are used when taking volume of solutions in which accuracy does not have to be very high. They are filled in the same way as volumetric ones and liquid can be gradually released.

serine    →   serin

Serine is neutral amino acids with polar side chains. It is one of two hydroxyl amino acids. Both are commonly considered to by hydrophilic due to the hydrogen bonding capacity of the hydroxyl group. Serine often serves as a nucleophile in many enzyme active sites, and is best known for its role in the serine proteases. Serine is a site of phosphorylation and glycosylation which is important for enzyme regulation and cell signaling. It is not essential to the human diet, since it is synthesized in the body from other metabolites, including glycine.

• Abbreviations: Ser, S
• IUPAC name: 2-amino-3-hydroxypropanoic acid
• Molecular formula: C₃H₇NO₃
• Molecular weight: 105.09 g/mol