CHEMISTRY GLOSSARY

nucleotide    →   nukleotid

Nucleotides are the components that made up nucleic acids. They have three major components: the first component is a nitrogenous base, which is derivative of one of two parent compounds, pyrimidine or purine; the second is a pentose, or five carbon sugar group; the third is a unit of phosphate. Each group of three nucleotides in a gene is known as a codon. Whenever the phosphate group is not present, a nucleotide becomes a nucleoside.

Ostwald’s viscometer    →   Ostwaldov viskozimetar

Ostwald viscometer, also known as U-tube viscometer or capillary viscometer is a device used to measure the viscosity of the liquid with a known density. The method of determining viscosity with this instrument consists of measuring the time for a known volume of the liquid (the volume contained between the marks A and B) to flow through the capillary under the influence of gravity. Ostwald viscometers named after the German chemist Wilhelm Ostwald (1853-1932).

The instrument must first be calibrated with materials of known viscosity such as pure (deionized) water. Knowing the value of viscosity of one liquid, one can calculate the viscosity of other liquid.

where η₁ and η₂ are viscosity coefficients of the liquid and water, and ρ₁ and ρ₂ are the densities of liquid and water, respectively.

potentiometric titration    →   potenciometrijska titracija

Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume. Types of potentiometric titrations for the determination of analytes in photoprocessing solutions include acid-base, redox, precipitation, and complexometric.

Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.

A titration curve has a characteristic sigmoid curve. The part of the curve that has the maximum change marks the equivalence point of the titration. The first derivative, ΔE/ΔV, is the slope of the curve, and the endpoint occurs at the volume, V', where ΔE/ΔV has the maximum value.

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.

redox titration    →   redoks-titracija

Redox titration (oxidation-reduction titration) is a titration based on a redox reaction. For example, iron in water can be determined by converting dissolved iron to Fe²⁺ and titrating the solution with potassium permanganate (KMnO₄), a powerful oxidising agent.

sedimentation    →   sedimentiranje

Sedimentation is a process of separating specifically heavier, suspended matter, than the solution is. Solid matter settles on the bottom of the vessel and the liquid above it is poured off. The settling zone is the largest portion of the sedimentation basin. This zone provides the calm area necessary for the suspended particles to settle. The sludge zone, located at the bottom of the tank, provides a storage area for the sludge before it is removed for additional treatment or disposal.

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.

thermometer    →   termometar

Thermometers are devices for measuring temperature. Linear and volume thermal expansion are macroscopic properties of matter, which can be easily measured, relative to measurements of microscopic properties, on the basis of which, temperature is defined. Thermometers based on thermal expansion are secondary instruments that is, they have to be calibrated in comparison to a standard thermometer. In a thermometer with liquid, mercury or alcohol is placed in a small glass container. If temperature increases, the liquid undergoes volume expansion and rises in a capillary. The level of the raised liquid is the measure of temperature. Mercury thermometers measure temperatures in the temperature range between -39 °C and 300 °C. Alcohol thermometers measure lower temperatures. Bimetal thermometers have a spiral spring, which consists of two metals with different coefficients of linear expansion. When temperature changes, metals undergo different change in length and the consequence twisting of the spring is transferred to a pointer, the deflection of which is the measure of temperature.

volumetric flask    →   odmjerna tikvica

Volumetric flasks are bottles made of glass, in a pear like in shape with long thin necks and flat bottoms. All come with a ground glass stopper for a tight seal. Volume marking is cut in glass with fluoride acid around the neck, so that parallax should be avoided (flask is put in front of the eyes so that one can see only a straight horizontal line). A volumetric flask is calibrated to contain (TC or In) the indicated volume of water at 20 °C when the bottom of the meniscus is adjusted to just rest on the center of the line marked on the neck of the flask. They are used for preparing the exactly known volume of sample solution and standard solutions of reagents. On each flask with volume designation a temperature on which the flask has been calibrated is designated.

volumetric pipette    →   prijenosna pipeta

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.