CHEMISTRY GLOSSARY

electrode of the first kind    →   elektroda prvog reda

Electrode of the first kind is a simple metal electrode immersed in a solution containing its own ion (e.g., silver immersed in a silver nitrate solution). The equilibrium potential of this electrode is a function of the concentration (more correctly of activity) of the cation of the electrode metal in the solution (see Nernst’s electrode potential equation).

Tyndall’s effect    →   Tyndallov efekt

Tyndall’s effect occurs when light disperses on colloid particles. This phenomenon can be seen when a ray of light enters in dark room through a small hole. In the beam some dust particles of colloid dimensions can be seen sparkling.

ultracentrifuge    →   ultracentrifuga

Ultracentrifuge is a high-speed centrifuge used in the separation of colloidal or submicroscopic particles. The ultracentrifuge can generate forces thousands or millions of times stronger than the force of gravity.

zeta potential    →   zeta potencijal

Zeta potential (ζ) is the potential across the interface of all solids and liquids. Specifically, the potential across the diffuse layer of ions surrounding a charged colloidal particle, which is largely responsible for colloidal stability. Also called electrokinetic potential.

electrode of the second kind    →   elektroda drugog reda

Electrodes of the second kind are metal electrodes assembly with the equilibrium potential being a function of the concentration of an anion in the solution. Typical examples are the silver/silver-chloride electrode and the calomel electrode. The potential of the metal is controlled by the concentration of its cation in the solution, but this, in turn, is controlled by the anion concentration in the solution through the solubility product of the slightly soluble metal salt. Contrast with electrode of the first kind and electrode of the third kind.

electrophoresis    →   elektroforeza

Electrophoresis is a technique for the analysis and separation of colloids, based on the movement of charged colloidal particles in an electric field. The migration is toward electrodes of charge opposite to that of the particles. The rate of migration of the particles depends on the field, the charge on the particles, and on other factors, such as the size and shape of the particles.

Electrophoresis is important in the study of proteins. The acidity of the solution can be used to control the direction in which a protein moves upon electrophoresis.

electroplating    →   galvaniziranje

Electroplating (also called electrodeposition) is the deposition of a metallic coating onto an object by putting a negative charge onto the object and immersing it into a solution which contains a salt of the metal to be deposited. The metallic ions of the salt carry a positive charge and are attracted to the part. When they reach it, the negatively charged part provides the electrons to reduce the positively charged ions to metallic form.

Typically, a brass or nickel object is coated with a layer of silver by making use of electrolysis of a silver solution, using the object to be coated as the cathode. The anode consist of pure silver, and the cathode is the object to be plated. The electrolyte is a mixure of silver nitrate with potassium cyanide. The reactions are:

The cyanide ensures a low concentration of silver ions, a condition for providing the best plating results.

erbium    →   erbij

Erbium was discovered by Carl Gustaf Mosander (Sweden) in 1843. Named after Ytterby, a village in Sweden. It is soft, malleable, silvery metal. Reacts slowly with water. Dissolves in acids. Metal ignites and burns readily. Erbium is found with other heavier rare earths in xenotime and euxenite. Erbium oxide is used in ceramics to obtain a pink glaze. Also a few uses in the nuclear industry and as an alloying agent for other exotic metals.

europium    →   europij

Europium was discovered by Eugene Demarcay (France) in 1896. Named for the continent of Europe. It is soft, silvery-white metal. Extremely reactive with oxygen and water. Europium is obtained from monazite sand, which is a mixture of phosphates of calcium, thorium, cerium and most other rare earths. Used with yttrium oxide to make red phosphors for colour televisions.

foam    →   pjena

Foams are dispersions of gases in liquids or solids. The gas globule may be of any size, from colloidal to macroscopic, as in soap bubbles. Bakers’ bread and sponge rubber are examples of solid foams. Typical liquid foams are those used in fire-fighting, shaving creams, etc. Foams made by mechanical incorporation of air are widely used in the food industry (e.g. whipped cream, egg white, ice cream, etc.). Foams can be stabilized by surfactants.