CHEMISTRY GLOSSARY

microchemistry    →   mikrokemija

Microchemistry is a branch of chemistry that concerns isolating, identifying and an analysis of very small quantities of sample (few mg). It uses delicate reactions, special equipment and microscopes.

gravimetry    →   gravimetrija

Gravimetry is the quantitative measurement of an analyte by weighing a pure, solid form of the analyte. Since gravimetric analysis is an absolute measurement, it is the principal method for analysing and preparing primary standards.

A typical experimental procedure to determine an unknown concentration of an analyte in a solution is as follows:

- quantitatively precipitate the analyte from the solution

- collect the precipitate by filtering and wash it to remove impurities

- dry the solid in an oven to remove the solvent

- weigh the solid on an analytical balance

- calculate the analyte concentration in the original solution based on the weight of the precipitate.

Kirchoff, Gustav    →   Kirchoff, Gustav

Gustav Kirchoff (1824-1887) was a German physicist who, with the chemist Robert Bunsen (1811-1899), laid the foundations of spectral analysis. He realized that the Fraunhofer lines in the Sun's spectrum were due to light from the photosphere being absorbed at those specific wavelengths by elements in the solar atmosphere. He also found that incandescent solids, liquids, and compressed gases emit a continuous spectrum. Use of the Bunsen burner in conjunction with a glass prism led to the development of the spectroscope in collaboration with the Bunsen and to the spectroscopic discovery of the elements rubidium (1860) and cesium (1861).

Kjeldahl’s method    →   Kjeldahlov postupak

Kjeldahl’s method is an analytical method for determination of nitrogen in certain organic compounds. The method was developed by the Danish chemist Johan Kjeldahl (1849-1900).

It involves addition of a small amount of anhydrous potassium sulphate to the test compound, followed by heating the mixture with concentrated sulphuric acid, often with a catalyst such as copper sulphate. As a result ammonia is formed. After alkalyzing the mixture with sodium hydroxyde, the ammonia is separated by distillation, collected in standard acid, and the nitrogen determined by back-titration.

1. Kjeldahl flask for decomposition (500 ml – macro or 100 ml - micro)
2. funnel for alkaline solution
3. Wagner tube (drop catcher)
4. condenser
5. absorption flask with known volume of standard acid

PCl5 reaction    →   reakcija s PCl5

Reaction with phosphorus pentachloride (PCl₅) is a characteristic of organic compounds containing a hydroxyl group and this reaction is used to identify these compounds in an organic analysis.

sample    →   uzorak

In chemical analysis total amount of matter is not analysed, but only a smaller part of it. This small part is called analysis sample and it must represent the whole amount of the matter that is being analysed.

spectroscopy    →   spektroskopija

Spectroscopy is the analysis of the lines of light emitted from excited atoms as the electrons drop back through their orbitals. These lines give the energy and distances of the electronic orbitals.

TISAB    →   TISAB

TISAB (Total Ionic Strength Adjustment Buffer) is a buffer solution which maintains a constant activity of an analyte in solution.

Knudsen burette    →   Knudsenova bireta

Knudsen's automatic bulb-burette, developed by the Danish physicist Martin Knudsen (1871-1949), is designed in a way that even routine field analysis in a boat laboratory would provide highly accurate measurements. The burette is filled with a mixture of silver nitrate from reservoir R, located above the burette, by opening the A valve. When the solution crosses the three-way C valve the A valve is closed preventing further solution flow in to the burette. Any extra solution is caught in the W bowl. Turn the C valve, which marks the zero on the scale, in order to allow atmospheric air to enter the burette. Since most open-ocean samples lie in a relatively small chlorinity range, the burette is designed so that much of its capacity is in the bulb (B). This allows the titration to be quick (by quickly releasing contents from the B area) and reduces the error that occurs from the slow drainage along the inner wall of the burette.

Each millimeter is divided in to twenty parts (double millimeter division of the Knudsen burette) which allows for highly accurate measurements (the scale is read up to a precision of 0.005 mL). From 0 to 16 the burette isn't divided, that usually starts from 16 and goes until 20.5 or 21.5. A single double millimeter on a Knudsen burette scale corresponds to one permille of chloride in the seawater sample. This burette can be used for titration of water from all of the oceans and seas, with the exemptions being areas with very low salinity (e.g. the Baltic Sea) and river estuaries which require the use of normal burettes.

mass spectrometry    →   masena spectrometrija

Mass spectrometry is an analytical technique in which ions are separated according to the mass/charge (m/e) ratio and detected by a suitable detector.

In a mass spectrometer a sample is ionised and the positive ions produced are accelerated into a high-vacuum region containing electric and magnetic fields. These fields deflect and focus the ions onto a detector. A mass spectrum is thus obtained, consisting of a series of peaks of variable intensity to which m/e values can be assigned. Different molecules can be identified by their characteristic pattern of lines.