CHEMISTRY GLOSSARY

acid-base indicator    →   kiselo-bazni indikator

Acid-base indicator is a weak acid or weak base, such as litmus, methyl orange or phenolphthalein, which changes colour when it gains or loses an H⁺ ion.

universal indicator    →   univerzalni indikator

Universal indicator is an indicator which undergoes several colour changes over a wide range of pH. The colour is used to indicate pH directly. Universal indicators are usually mixtures of several indicators.

indicator    →   indikator

Indicator is a substance used to show the presence of a chemical substance or ion by its colour. Acid-base indicators are compounds, such as phenolphtaleine and methyl orange, which change colour reversibly, depending on whether the solution is acidic or basic. Oxidation-reduction indicators are substances that show a reversible colour change between oxidised and reduced forms.

radioactive indicator    →   radioaktivni indikator

By use of suitable radioactive isotopes biochemical processes can be observed in plants, animals and humans, by measuring radioactive radiation of radioactive indicator. Artificial radioactive isotopes have the same chemical properties as natural ones, which enable us to mark those natural isotopes with addition of artificial ones and in this way follow the path of those elements during a chemical reaction. One of the most important radioactive indicators is the radioactive carbon ¹⁴C.

indicator electrode    →   indikatorska elektroda

Indicator electrode is working in one of the electrodes in some classical two-electrode cells, e.g., in a potentiometric electroanalytical setup where the potential of the measuring electrode (against a reference electrode) is a measure of the concentration (more accurately activity) of a species in the solution.

acid-base titration    →   kiselo-bazna titracija

Acid-base titration is an analytical technique in volumetric analysis, where an acid of known concentration is used to neutralise a known volume of a base, and the observed volume of the acid required is used to determine the unknown concentration of the base. An acid-base indicator is used to determine the end-point of the titration.

artificial radioactive isotope    →   umjetni radioaktivni izotop

Artificial radioactive isotopes are formed when an atom is bombed with an accelerator or exposing it to slow moving neutrons in a nuclear reactor. In this way isotopes (radionuclides) are obtained which are non-existent in nature because of their unstability and radioactive transition into stable isotopes. Most important radioactive isotopes are:

Radioactive isotope of cobalt is formed when ordinary metal cobalt is bombed with neutrons in a nuclear reactor.

Radioactive isotope of phosphorus is formed when ordinary phosphorus is bombed with deuterons produced in cyclotron.

radioactive isotope of carbon is formed when a nitrogen is bombed with slow moving neutrons in a nuclear reactor. It is mostly used as a radioactive indicator.

litmus paper    →   lakmus-papir

Litmus paper is an unsized paper treated with litmus for the use as an acid-base indicator, in an acid it turns red, and in a base it turns blue.

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

methyl orange    →   metil oranž

Methyl orange is an acid-base indicator, in acid it turns red and in a base it turns yellow.