CHEMISTRY GLOSSARY

mucopolysaccharide    →   mukopolisaharid

Mucopolysaccharides are carbohydrates that can be found in cellular membranes of bacteria.

osmosis    →   osmoza

Osmosis is the flow of a solvent in a system in which two solutions of different concentration are separated by a semipermeable membrane which cannot pass solute molecules. The solvent will flow from the side of lower concentration to that of higher concentration, thus tending to equalise the concentrations. The pressure that must be applied to the more concentrated side to stop the flow is called the osmotic pressure.

reverse osmosis    →   reverzna osmoza

Reverse osmosis is the method used for obtaining freshwater from saltwater. The process uses a semi-permeable membrane through which pure water and not the salts will pass. The saltwater must be pressurised to approximately 25 bar, which makes it operationally expensive to produce large quantities of fresh water by this method.

glass electrode    →   staklena elektroda

Glass electrode is a hydrogen-ion responsive electrode usually consisting of a bulb, or other suitable form, of special glass attached to a stem of high resistance glass complete with internal reference electrode and internal filling solution system. Glass electrode is also available for the measurement of sodium ions.

The glass electrode, which consists of a thin wall glass bulb, has an extremely high electrical resistance. The membrane of a typical glass electrode (with a thickness of 0.03 mm to 0.1 mm) has an electrical resistance of 30 MΩ to 600 MΩ. The surface of a glass membrane must be hydrated before it will function as a pH electrode. When a glass surface is immersed in an aqueous solution then a thin solvated layer (gel layer) is formed on the glass surface in which the glass structure is softer. This applies to both the outside and inside of the glass membrane.

The simplest explanation for the working of the thin glass electrode is that the glass acts as a weak acid (Glass-H).

The hydrogen ion activity of the internal solution is held constant. When a solution of different pH from the inside comes in contact with the outside of the glass membrane, the glass is either deprotonated or protonated relative to the inside of the glass. The difference in pH between solutions inside and outside the thin glass membrane creates electromotive force in proportion to this difference in pH.

ion selective electrode    →   ion selektivne elektrode

Ion selective electrode (ISE) is an electrode or electrode assembly with a potential that is dependent on the concentration of an ionic species in the test solution and is used for electroanalysis. Ion-selective electrodes are often membrane type electrodes.

surface tension    →   površinska napetost

Surface tension (σ) is a property of liquids arising from unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane. As a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane.

osmotic pressure    →   osmotski tlak

Osmotic pressure (Π) is the excess pressure necessary to maintain osmotic equilibrium between a solution and a pure solvent separated by a membrane permeable only to the solvent. In an ideal dilute solution

where c_B is the amount-of-substance concentration of the solute, R is the molar gas constant, and T the temperature.

CO2 ion selective electrode    →   CO2 ion selektivna elektroda

The carbon dioxide ion selective electrode uses a gas-permeable membrane to separate the sample solution from the electrode internal solution. Dissolved carbon dioxide in the sample solution diffuses through the membrane until an equilibrium is reached between the partial pressure of CO₂ in the sample solution and the CO₂ in the internal filling solution. In any given sample the partial pressure of carbon dioxide will be proportional to the concentration of carbon dioxide. The diffusion across the membrane affects the level of hydrogen ions in the internal filling solution:

The hydrogen level of the internal filling solution is measured by the pH electrode located behind the membrane. The internal filling solution contains a high concentration of sodium bicarbonate (e.g. 0.1 mol/L NaHCO₃) so that the bicarbonate level can be considered constant.